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Roman CCS White Paper: Optimizing the HLTDS Cadence at Fixed Depth: The current proposal for the High Latitude Time Domain Survey (HLTDS) is two
tiers (wide and deep) of multi-band imaging and prism spectroscopy with a
cadence of five days (Rose et al., 2021). The five-day cadence is motivated by
the desire to measure mid-redshift SNe where time dilation is modest as well as
to better photometrically characterize the transients detected. This white
paper does not provide a conclusion as to the best cadence for the HLTDS.
Rather, it collects a set of considerations that should be used for a careful
study of cadence by a future committee optimizing the Roman survey. This study
should optimize the HLTDS for both SN Ia cosmology and other transient science. | astro-ph_IM |
Optimizing Gravitational-Wave Detector Design for Squeezed Light: Achieving the quantum noise targets of third-generation detectors will
require 10 dB of squeezed-light enhancement as well as megawatt laser power in
the interferometer arms - both of which require unprecedented control of the
internal optical losses. In this work, we present a novel optimization approach
to gravitational-wave detector design aimed at maximizing the robustness to
common, yet unavoidable, optical fabrication and installation errors, which
have caused significant loss in Advanced LIGO. As a proof of concept, we employ
these techniques to perform a two-part optimization of the LIGO A+ design.
First, we optimize the arm cavities for reduced scattering loss in the presence
of point absorbers, as currently limit the operating power of Advanced LIGO.
Then, we optimize the signal recycling cavity for maximum squeezing
performance, accounting for realistic errors in the positions and radii of
curvature of the optics. Our findings suggest that these techniques can be
leveraged to achieve substantially greater quantum noise performance in current
and future gravitational-wave detectors. | astro-ph_IM |
Design and optimization of a dispersive unit based on cascaded volume
phase holographic gratings: We describe a dispersive unit consisting of cascaded volume-phase holographic
gratings for spectroscopic applications. Each of the gratings provides high
diffractive efficiency in a relatively narrow wavelength range and transmits
the rest of the radiation to the 0th order of diffraction. The spectral lines
formed by different gratings are centered in the longitudal direction and
separated in the transverse direction due to tilt of the gratings around two
axes. We consider a technique of design and optimization of such a scheme. It
allows to define modulation of index of refraction and thickness of the
holographic layer for each of the gratings as well as their fringes frequencies
and inclination angles. At the first stage the gratings parameters are found
approximately using analytical expressions of Kogelnik's coupled wave theory.
Then each of the grating starting from the longwave sub-range is optimized
separately by using of numerical optimization procedure and rigorous coupled
wave analysis to achieve a high diffraction efficiency profile with a steep
shortwave edge. In parallel such targets as ray aiming and linear dispersion
maintenance are controlled by means of ray tracing. We demonstrate this
technique on example of a small-sized spectrograph for astronomical
applications. It works in the range of 500-650 nm and uses three gratings
covering 50 nm each. It has spectral resolution of 6130 - 12548. Obtaining of
the asymmetrical efficiency curve is shown with use of dichromated gelatin and
a photopolymer. Change of the curve shape allows to increase filling
coefficient for the target sub-range up to 2.3 times. | astro-ph_IM |
IVOA Recommendation: Simple Cone Search Version 1.03: This specification defines a simple query protocol for retrieving records
from a catalog of astronomical sources. The query describes sky position and an
angular distance, defining a cone on the sky. The response returns a list of
astronomical sources from the catalog whose positions lie within the cone,
formatted as a VOTable. This version of the specification is essentially a
transcription of the original Cone Search specification in order to move it
into the IVOA standardization process. | astro-ph_IM |
Intrinsic Instrumental Polarization and High-Precision Pulsar Timing: Radio telescopes are used to accurately measure the time of arrival (ToA) of
radio pulses in pulsar timing experiments that target mostly millisecond
pulsars (MSPs) due to their high rotational stability. This allows for detailed
study of MSPs and forms the basis of experiments to detect gravitational waves.
Apart from intrinsic and propagation effects, such as pulse-to-pulse jitter and
dispersion variations in the interstellar medium, timing precision is limited
in part by the following: polarization purity of the telescope's orthogonally
polarized receptors, the signal-to-noise ratio (S/N) of the pulsar profile, and
the polarization fidelity of the system. Using simulations, we present how
fundamental limitations in recovering the true polarization reduce the
precision of ToA measurements. Any real system will respond differently to each
source observed depending on the unique pulsar polarization profile. Using the
profiles of known MSPs we quantify the limits of observing system
specifications that yield satisfactory ToA measurements, and we place a
practical design limit beyond which improvement of the system results in
diminishing returns. Our aim is to justify limits for the front-end
polarization characteristics of next generation radio telescopes, leading to
the Square Kilometre Array (SKA). | astro-ph_IM |
Effects of transients in LIGO suspensions on searches for gravitational
waves: This paper presents an analysis of the transient behavior of the Advanced
LIGO suspensions used to seismically isolate the optics. We have characterized
the transients in the longitudinal motion of the quadruple suspensions during
Advanced LIGO's first observing run. Propagation of transients between stages
is consistent with modelled transfer functions, such that transient motion
originating at the top of the suspension chain is significantly reduced in
amplitude at the test mass. We find that there are transients seen by the
longitudinal motion monitors of quadruple suspensions, but they are not
significantly correlated with transient motion above the noise floor in the
gravitational wave strain data, and therefore do not present a dominant source
of background noise in the searches for transient gravitational wave signals. | astro-ph_IM |
The Eleventh and Twelfth Data Releases of the Sloan Digital Sky Survey:
Final Data from SDSS-III: The third generation of the Sloan Digital Sky Survey (SDSS-III) took data
from 2008 to 2014 using the original SDSS wide-field imager, the original and
an upgraded multi-object fiber-fed optical spectrograph, a new near-infrared
high-resolution spectrograph, and a novel optical interferometer. All the data
from SDSS-III are now made public. In particular, this paper describes Data
Release 11 (DR11) including all data acquired through 2013 July, and Data
Release 12 (DR12) adding data acquired through 2014 July (including all data
included in previous data releases), marking the end of SDSS-III observing.
Relative to our previous public release (DR10), DR12 adds one million new
spectra of galaxies and quasars from the Baryon Oscillation Spectroscopic
Survey (BOSS) over an additional 3000 sq. deg of sky, more than triples the
number of H-band spectra of stars as part of the Apache Point Observatory (APO)
Galactic Evolution Experiment (APOGEE), and includes repeated accurate radial
velocity measurements of 5500 stars from the Multi-Object APO Radial Velocity
Exoplanet Large-area Survey (MARVELS). The APOGEE outputs now include measured
abundances of 15 different elements for each star. In total, SDSS-III added
2350 sq. deg of ugriz imaging; 155,520 spectra of 138,099 stars as part of the
Sloan Exploration of Galactic Understanding and Evolution 2 (SEGUE-2) survey;
2,497,484 BOSS spectra of 1,372,737 galaxies, 294,512 quasars, and 247,216
stars over 9376 sq. deg; 618,080 APOGEE spectra of 156,593 stars; and 197,040
MARVELS spectra of 5,513 stars. Since its first light in 1998, SDSS has imaged
over 1/3 of the Celestial sphere in five bands and obtained over five million
astronomical spectra. | astro-ph_IM |
Probing the Spacetime Around Supermassive Black Holes with Ejected
Plasma Blobs: Millimeter-wavelength VLBI observations of the supermassive black holes in
Sgr A* and M87 by the Event Horizon Telescope could potentially trace the
dynamics of ejected plasma blobs in real time. We demonstrate that the
trajectory and tidal stretching of these blobs can be used to test general
relativity and set new constraints on the mass and spin of these black holes. | astro-ph_IM |
SISPO: Space Imaging Simulator for Proximity Operations: This paper describes the architecture and demonstrates the capabilities of a
newly developed, physically-based imaging simulator environment called SISPO,
developed for small solar system body fly-by and terrestrial planet surface
mission simulations. The image simulator utilises the open-source 3D
visualisation system Blender and its Cycles rendering engine, which supports
physically based rendering capabilities and procedural micropolygon
displacement texture generation. The simulator concentrates on realistic
surface rendering and has supplementary models to produce realistic dust- and
gas-environment optical models for comets and active asteroids. The framework
also includes tools to simulate the most common image aberrations, such as
tangential and sagittal astigmatism, internal and external comatic aberration,
and simple geometric distortions. The model framework's primary objective is to
support small-body space mission design by allowing better simulations for
characterisation of imaging instrument performance, assisting mission planning,
and developing computer-vision algorithms. SISPO allows the simulation of
trajectories, light parameters and camera's intrinsic parameters. | astro-ph_IM |
The PLATO Payload Data Processing System SpaceWire network: PLATO has been selected and adopted by ESA as the third medium-class Mission
(M3) of the Cosmic Vision Program, to be launched in 2026 with a Soyuz-Fregat
rocket from the French Guiana. Its Payload is based on a suite of 26 telescopes
and cameras in order to discover and characterise, thanks to ultra-high
accurate photometry and the transits method, new exoplanets down to the range
of Earth analogues. Each camera is composed of 4 CCDs working in full frame or
frame-transfer mode. 24 cameras out of 26 host 4510 by 4510 pixels CCDs,
operated in full-frame mode with a pixel depth of 16 bits and a cadence of 25
s. Given the huge data volume to be managed, the PLATO Payload relies on an
efficient Data Processing System (DPS) whose Units perform images windowing,
cropping and compression. Each camera and DPS Unit is connected to a fast
SpaceWire network running at 100 MHz and interfaced to the satellite On-Board
Computer by means of an Instrument Control Unit (ICU), performing data
collection and compression. | astro-ph_IM |
Strong Lens Time Delay Challenge: I. Experimental Design: The time delays between point-like images in gravitational lens systems can
be used to measure cosmological parameters. The number of lenses with measured
time delays is growing rapidly; the upcoming \emph{Large Synoptic Survey
Telescope} (LSST) will monitor $\sim10^3$ strongly lensed quasars. In an effort
to assess the present capabilities of the community to accurately measure the
time delays, and to provide input to dedicated monitoring campaigns and future
LSST cosmology feasibility studies, we have invited the community to take part
in a "Time Delay Challenge" (TDC). The challenge is organized as a set of
"ladders," each containing a group of simulated datasets to be analyzed blindly
by participating teams. Each rung on a ladder consists of a set of realistic
mock observed lensed quasar light curves, with the rungs' datasets increasing
in complexity and realism. The initial challenge described here has two
ladders, TDC0 and TDC1. TDC0 has a small number of datasets, and is designed to
be used as a practice set by the participating teams. The (non-mandatory)
deadline for completion of TDC0 was the TDC1 launch date, December 1, 2013. The
TDC1 deadline was July 1 2014. Here we give an overview of the challenge, we
introduce a set of metrics that will be used to quantify the goodness-of-fit,
efficiency, precision, and accuracy of the algorithms, and we present the
results of TDC0. Thirteen teams participated in TDC0 using 47 different
methods. Seven of those teams qualified for TDC1, which is described in the
companion paper II. | astro-ph_IM |
IVOA Recommendation: IVOA Astronomical Data Query Language Version 2.00: This document describes the Astronomical Data Query Language (ADQL). ADQL has
been developed based on SQL92. This document describes the subset of the SQL
grammar supported by ADQL. Special restrictions and extensions to SQL92 have
been defined in order to support generic and astronomy specific operations. | astro-ph_IM |
Woofer-tweeter deformable mirror control for closed-loop adaptive
optics: theory and practice: Deformable mirrors with very high order correction generally have smaller
dynamic range of motion than what is required to correct seeing over large
aperture telescopes. As a result, systems will need to have an architecture
that employs two deformable mirrors in series, one for the low-order but large
excursion parts of the wavefront and one for the finer and smaller excursion
components. The closed-loop control challenge is to a) keep the overall system
stable, b) avoid the two mirrors using control energy to cancel each other's
correction, c) resolve actuator saturations stably, d) assure that on average
the mirrors are each correcting their assigned region of spatial frequency
space. We present the control architecture and techniques for assuring that it
is linear and stable according to the above criteria. We derived the analytic
forms for stability and performance and show results from simulations and
on-sky testing using the new ShaneAO system on the Lick 3-meter telescope. | astro-ph_IM |
Background analysis and status of the ANAIS dark matter project: ANAIS (Annual modulation with NaI Scintillators) is a project aiming to set
up at the new facilities of the Canfranc Underground Laboratory (LSC), a large
scale NaI(Tl) experiment in order to explore the DAMA/LIBRA annual modulation
positive result using the same target and technique. Two 12.5 kg each NaI(Tl)
crystals provided by Alpha Spectra took data at the LSC in the ANAIS-25 set-up.
The comparison of the background model for the ANAIS-25 prototypes with the
experimental results is presented. ANAIS crystal radiopurity goals have been
achieved for Th-232 and U-238 chains, but a Pb-210 contamination
out-of-equilibrium was identified, whose origin has been studied. The high
light collection efficiency obtained with these prototypes allows to anticipate
an energy threshold of the order of 1 keVee. A new detector, with improved
performances, was received in March 2015 and very preliminary results are
shown. | astro-ph_IM |
Gaia Data Release 3: Gaia scan-angle dependent signals and spurious
periods: Context: Gaia DR3 time series data may contain spurious signals related to
the time-dependent scan angle. Aims: We aim to explain the origin of scan-angle
dependent signals and how they can lead to spurious periods, provide statistics
to identify them in the data, and suggest how to deal with them in Gaia DR3
data and in future releases. Methods: Using real Gaia data, alongside numerical
and analytical models, we visualise and explain the features observed in the
data. Results: We demonstrated with Gaia data that source structure
(multiplicity or extendedness) or pollution from close-by bright objects can
cause biases in the image parameter determination from which photometric,
astrometric and (indirectly) radial velocity time series are derived. These
biases are a function of the time-dependent scan direction of the instrument
and thus can introduce scan-angle dependent signals, which in turn can result
in specific spurious periodic signals. Numerical simulations qualitatively
reproduce the general structure observed in the spurious period and spatial
distribution of photometry and astrometry. A variety of statistics allows for
identification of affected sources. Conclusions: The origin of the scan-angle
dependent signals and subsequent spurious periods is well-understood and is in
majority caused by fixed-orientation optical pairs with separation <0.5"
(amongst which binaries with P>>5y) and (cores of) distant galaxies. Though the
majority of sources with affected derived parameters have been filtered out
from the Gaia archive, there remain Gaia DR3 data that should be treated with
care (e.g. gaia_source was untouched). Finally, the various statistics
discussed in the paper can not only be used to identify and filter affected
sources, but alternatively reveal new information about them not available
through other means, especially in terms of binarity on sub-arcsecond scale. | astro-ph_IM |
An elastic lidar system for the H.E.S.S. Experiment: The H.E.S.S. experiment in Namibia, Africa, is a high energy gamma ray tele-
scope sensitive in the energy range from 100 Gev to a few tens of TeV, via the
use of the atmospheric Cherenkov technique. To minimize the systematic errors
on the derived fluxes of the measured sources, one has to calculate the impact
of the atmospheric properties, in particular the extinction parameter of the
Cherenkov light ( 300-650 nm) exploited to observe and reconstruct atmospheric
particle showers initiated by gamma-ray photons. A lidar can provide this kind
of information for some given wavelengths within this range. In this paper we
report on the hardware components, operation and data acquisition of such a
system installed at the H.E.S.S. site. | astro-ph_IM |
Large-aperture wide-bandwidth antireflection-coated silicon lenses for
millimeter wavelengths: The increasing scale of cryogenic detector arrays for sub-millimeter and
millimeter wavelength astrophysics has led to the need for large aperture, high
index of refraction, low loss, cryogenic refracting optics. Silicon with n =
3.4, low loss, and relatively high thermal conductivity is a nearly optimal
material for these purposes, but requires an antireflection (AR) coating with
broad bandwidth, low loss, low reflectance, and a matched coefficient of
thermal expansion. We present an AR coating for curved silicon optics comprised
of subwavelength features cut into the lens surface with a custom three axis
silicon dicing saw. These features constitute a metamaterial that behaves as a
simple dielectric coating. We have fabricated and coated silicon lenses as
large as 33.4 cm in diameter with coatings optimized for use between 125-165
GHz. Our design reduces average reflections to a few tenths of a percent for
angles of incidence up to 30 degrees with low cross-polarization. We describe
the design, tolerance, manufacture, and measurements of these coatings and
present measurements of the optical properties of silicon at millimeter
wavelengths at cryogenic and room temperatures. This coating and lens
fabrication approach is applicable from centimeter to sub-millimeter
wavelengths and can be used to fabricate coatings with greater than octave
bandwidth. | astro-ph_IM |
Non-linear parameter estimation for the LTP experiment: analysis of an
operational exercise: The precursor ESA mission LISA-Pathfinder, to be flown in 2013, aims at
demonstrating the feasibility of the free-fall, necessary for LISA, the
upcoming space-born gravitational wave observatory. LISA Technology Package
(LTP) is planned to carry out a number of experiments, whose main targets are
to identify and measure the disturbances on each test-mass, in order to reach
an unprecedented low-level residual force noise. To fulfill this plan, it is
then necessary to correctly design, set-up and optimize the experiments to be
performed on-flight and do a full system parameter estimation. Here we describe
the progress on the non-linear analysis using the methods developed in the
framework of the \textit{LTPDA Toolbox}, an object-oriented MATLAB Data
Analysis environment: the effort is to identify the critical parameters and
remove the degeneracy by properly combining the results of different
experiments coming from a closed-loop system like LTP. | astro-ph_IM |
Galaxy Image Classification using Hierarchical Data Learning with
Weighted Sampling and Label Smoothing: With the development of a series of Galaxy sky surveys in recent years, the
observations increased rapidly, which makes the research of machine learning
methods for galaxy image recognition a hot topic. Available automatic galaxy
image recognition researches are plagued by the large differences in similarity
between categories, the imbalance of data between different classes, and the
discrepancy between the discrete representation of Galaxy classes and the
essentially gradual changes from one morphological class to the adjacent class
(DDRGC). These limitations have motivated several astronomers and machine
learning experts to design projects with improved galaxy image recognition
capabilities. Therefore, this paper proposes a novel learning method,
``Hierarchical Imbalanced data learning with Weighted sampling and Label
smoothing" (HIWL). The HIWL consists of three key techniques respectively
dealing with the above-mentioned three problems: (1) Designed a hierarchical
galaxy classification model based on an efficient backbone network; (2)
Utilized a weighted sampling scheme to deal with the imbalance problem; (3)
Adopted a label smoothing technique to alleviate the DDRGC problem. We applied
this method to galaxy photometric images from the Galaxy Zoo-The Galaxy
Challenge, exploring the recognition of completely round smooth, in between
smooth, cigar-shaped, edge-on and spiral. The overall classification accuracy
is 96.32\%, and some superiorities of the HIWL are shown based on recall,
precision, and F1-Score in comparing with some related works. In addition, we
also explored the visualization of the galaxy image features and model
attention to understand the foundations of the proposed scheme. | astro-ph_IM |
STROBE-X: X-ray Timing and Spectroscopy on Dynamical Timescales from
Microseconds to Years: We present the Spectroscopic Time-Resolving Observatory for Broadband Energy
X-rays (STROBE-X), a probe-class mission concept selected for study by NASA. It
combines huge collecting area, high throughput, broad energy coverage, and
excellent spectral and temporal resolution in a single facility. STROBE-X
offers an enormous increase in sensitivity for X-ray spectral timing, extending
these techniques to extragalactic targets for the first time. It is also an
agile mission capable of rapid response to transient events, making it an
essential X-ray partner facility in the era of time-domain, multi-wavelength,
and multi-messenger astronomy. Optimized for study of the most extreme
conditions found in the Universe, its key science objectives include: (1)
Robustly measuring mass and spin and mapping inner accretion flows across the
black hole mass spectrum, from compact stars to intermediate-mass objects to
active galactic nuclei. (2) Mapping out the full mass-radius relation of
neutron stars using an ensemble of nearly two dozen rotation-powered pulsars
and accreting neutron stars, and hence measuring the equation of state for
ultradense matter over a much wider range of densities than explored by NICER.
(3) Identifying and studying X-ray counterparts (in the post-Swift era) for
multiwavelength and multi-messenger transients in the dynamic sky through
cross-correlation with gravitational wave interferometers, neutrino
observatories, and high-cadence time-domain surveys in other electromagnetic
bands. (4) Continuously surveying the dynamic X-ray sky with a large duty cycle
and high time resolution to characterize the behavior of X-ray sources over an
unprecedentedly vast range of time scales. STROBE-X's formidable capabilities
will also enable a broad portfolio of additional science. | astro-ph_IM |
Historical astronomical data: urgent need for preservation, digitization
enabling scientific exploration: Over the past decades and even centuries, the astronomical community has
accumulated a signif-icant heritage of recorded observations of a great many
astronomical objects. Those records con-tain irreplaceable information about
long-term evolutionary and non-evolutionary changes in our Universe, and their
preservation and digitization is vital. Unfortunately, most of those data risk
becoming degraded and thence totally lost. We hereby call upon the astronomical
community and US funding agencies to recognize the gravity of the situation,
and to commit to an interna-tional preservation and digitization efforts
through comprehensive long-term planning supported by adequate resources,
prioritizing where the expected scientific gains, vulnerability of the
origi-nals and availability of relevant infrastructure so dictates. The
importance and urgency of this issue has been recognized recently by General
Assembly XXX of the International Astronomical Union (IAU) in its Resolution
B3: "on preservation, digitization and scientific exploration of his-torical
astronomical data". We outline the rationale of this promotion, provide
examples of new science through successful recovery efforts, and review the
potential losses to science if nothing it done. | astro-ph_IM |
Homography-Based Correction of Positional Errors in MRT Survey: The Mauritius Radio Telescope (MRT) images show systematics in the positional
errors of sources when compared to source positions in the Molonglo Reference
Catalogue (MRC). We have applied two-dimensional homography to correct
positional errors in the image domain and avoid re-processing the visibility
data. Positions of bright (above 15-$\sigma$) sources, common to MRT and MRC
catalogues, are used to set up an over-determined system to solve for the 2-D
homography matrix. After correction, the errors are found to be within 10% of
the beamwidth for these bright sources and the systematics are eliminated from
the images. | astro-ph_IM |
SAT.STFR.FRQ (UWA) Detail Design Report (MID): The Square Kilometre Array (SKA) project is an international effort to build
the world's most sensitive radio telescope operating in the 50 MHz to 14 GHz
frequency range. Construction of the SKA is divided into phases, with the first
phase (SKA1) accounting for the first 10% of the telescope's receiving
capacity. During SKA1, a Low-Frequency Aperture Array (LFAA) comprising over a
hundred thousand individual dipole antenna elements will be constructed in
Western Australia (SKA1-LOW), while an array of 197 parabolic-receptor
antennas, incorporating the 64 receptors of MeerKAT, will be constructed in
South Africa (SKA1-MID).
Radio telescope arrays, such as the SKA, require phase-coherent reference
signals to be transmitted to each antenna site in the array. In the case of the
SKA, these reference signals are generated at a central site and transmitted to
the antenna sites via fibre-optic cables up to 175 km in length. Environmental
perturbations affect the optical path length of the fibre and act to degrade
the phase stability of the reference signals received at the antennas, which
has the ultimate effect of reducing the fidelity and dynamic range of the data
. Given the combination of long fibre distances and relatively high frequencies
of the transmitted reference signals, the SKA needs to employ
actively-stabilised frequency transfer technologies to suppress the fibre-optic
link noise in order to maintain phase-coherence across the array. | astro-ph_IM |
Understanding synthesis imaging dynamic range: We develop a general framework for quantifying the many different
contributions to the noise budget of an image made with an array of dishes or
aperture array stations. Each noise contribution to the visibility data is
associated with a relevant correlation timescale and frequency bandwidth so
that the net impact on a complete observation can be assessed. All quantities
are parameterised as function of observing frequency and the visibility
baseline length. We apply the resulting noise budget analysis to a wide range
of existing and planned telescope systems that will operate between about 100
MHz and 5 GHz to ascertain the magnitude of the calibration challenges that
they must overcome to achieve thermal noise limited performance. We conclude
that calibration challenges are increased in several respects by small
dimensions of the dishes or aperture array stations. It will be more
challenging to achieve thermal noise limited performance using 15 m class
dishes rather than the 25 m dishes of current arrays. Some of the performance
risks are mitigated by the deployment of phased array feeds and more with the
choice of an (alt,az,pol) mount, although a larger dish diameter offers the
best prospects for risk mitigation. Many improvements to imaging performance
can be anticipated at the expense of greater complexity in calibration
algorithms. However, a fundamental limitation is ultimately imposed by an
insufficient number of data constraints relative to calibration variables. The
upcoming aperture array systems will be operating in a regime that has never
previously been addressed, where a wide range of effects are expected to exceed
the thermal noise by two to three orders of magnitude. Achieving routine
thermal noise limited imaging performance with these systems presents an
extreme challenge. The magnitude of that challenge is inversely related to the
aperture array station diameter. | astro-ph_IM |
Unveiling the Dynamic Infrared Sky with Gattini-IR: While optical and radio transient surveys have enjoyed a renaissance over the
past decade, the dynamic infrared sky remains virtually unexplored. The
infrared is a powerful tool for probing transient events in dusty regions that
have high optical extinction, and for detecting the coolest of stars that are
bright only at these wavelengths. The fundamental roadblocks in studying the
infrared time-domain have been the overwhelmingly bright sky background (250
times brighter than optical) and the narrow field-of-view of infrared cameras
(largest is 0.6 sq deg). To begin to address these challenges and open a new
observational window in the infrared, we present Palomar Gattini-IR: a 25 sq
degree, 300mm aperture, infrared telescope at Palomar Observatory that surveys
the entire accessible sky (20,000 sq deg) to a depth of 16.4 AB mag (J band,
1.25um) every night. Palomar Gattini-IR is wider in area than every existing
infrared camera by more than a factor of 40 and is able to survey large areas
of sky multiple times. We anticipate the potential for otherwise infeasible
discoveries, including, for example, the elusive electromagnetic counterparts
to gravitational wave detections. With dedicated hardware in hand, and a F/1.44
telescope available commercially and cost-effectively, Palomar Gattini-IR will
be on-sky in early 2017 and will survey the entire accessible sky every night
for two years. Palomar Gattini-IR will pave the way for a dual hemisphere,
infrared-optimized, ultra-wide field high cadence machine called Turbo
Gattini-IR. To take advantage of the low sky background at 2.5 um, two
identical systems will be located at the polar sites of the South Pole,
Antarctica and near Eureka on Ellesmere Island, Canada. Turbo Gattini-IR will
survey 15,000 sq. degrees to a depth of 20AB, the same depth of the VISTA VHS
survey, every 2 hours with a survey efficiency of 97%. | astro-ph_IM |
Multimessenger Astronomy and Astrophysics Synergies: A budget neutral strategy is proposed for NSF to lead the implementation of
multimessenger astronomy and astrophysics, as outlined in the Astro2010 Decadal
Survey. The emerging capabilities for simultaneous measurements of physical and
astronomical data through the different windows of electromagnetic, hadronic
and gravitational radiation processes call for a vigorous pursuit of new
synergies. The proposed approach is aimed at the formation of new
collaborations and multimessenger data-analysis, to transcend the scientific
inquiries made within a single window of observations. In view of budgetary
constraints, we propose to include the multimessenger dimension in the ranking
of proposals submitted under existing NSF programs. | astro-ph_IM |
Sensitivity curves for searches for gravitational-wave backgrounds: We propose a graphical representation of detector sensitivity curves for
stochastic gravitational-wave backgrounds that takes into account the increase
in sensitivity that comes from integrating over frequency in addition to
integrating over time. This method is valid for backgrounds that have a
power-law spectrum in the analysis band. We call these graphs "power-law
integrated curves." For simplicity, we consider cross-correlation searches for
unpolarized and isotropic stochastic backgrounds using two or more detectors.
We apply our method to construct power-law integrated sensitivity curves for
second-generation ground-based detectors such as Advanced LIGO, space-based
detectors such as LISA and the Big Bang Observer, and timing residuals from a
pulsar timing array. The code used to produce these plots is available at
https://dcc.ligo.org/LIGO-P1300115/public for researchers interested in
constructing similar sensitivity curves. | astro-ph_IM |
The performance of the bolometer array and readout system during the
2012/2013 flight of the E and B experiment (EBEX): EBEX is a balloon-borne telescope designed to measure the polarization of the
cosmic microwave background radiation. During its eleven day science flight in
the Austral Summer of 2012, it operated 955 spider-web transition edge sensor
(TES) bolometers separated into bands at 150, 250 and 410 GHz. This is the
first time that an array of TES bolometers has been used on a balloon platform
to conduct science observations. Polarization sensitivity was provided by a
wire grid and continuously rotating half-wave plate. The balloon implementation
of the bolometer array and readout electronics presented unique development
requirements. Here we present an outline of the readout system, the remote
tuning of the bolometers and Superconducting QUantum Interference Device
(SQUID) amplifiers, and preliminary current noise of the bolometer array and
readout system. | astro-ph_IM |
Detectability of Galactic Faraday Rotation in Multi-wavelength CMB
Observations: A Cross-Correlation Analysis of CMB and Radio Maps: We introduce a new cross-correlation method to detect and verify the
astrophysical origin of Faraday Rotation (FR) in multiwavelength surveys. FR is
well studied in radio astronomy from radio point sources but the $\lambda^{2}$
suppression of FR makes detecting and accounting for this effect difficult at
millimeter and sub-millimeter wavelengths. Therefore statistical methods are
used to attempt to detect FR in the cosmic microwave background (CMB). Most
estimators of the FR power spectrum rely on single frequency data. In contrast,
we investigate the correlation of polarized CMB maps with FR measure maps from
radio point sources. We show a factor of $\sim30$ increase in sensitivity over
single frequency estimators and predict detections exceeding $10\sigma$
significance for a CMB-S4 like experiment. Improvements in observations of FR
from current and future radio polarization surveys will greatly increase the
usefulness of this method. | astro-ph_IM |
Conditional Density Estimation Tools in Python and R with Applications
to Photometric Redshifts and Likelihood-Free Cosmological Inference: It is well known in astronomy that propagating non-Gaussian prediction
uncertainty in photometric redshift estimates is key to reducing bias in
downstream cosmological analyses. Similarly, likelihood-free inference
approaches, which are beginning to emerge as a tool for cosmological analysis,
require a characterization of the full uncertainty landscape of the parameters
of interest given observed data. However, most machine learning (ML) or
training-based methods with open-source software target point prediction or
classification, and hence fall short in quantifying uncertainty in complex
regression and parameter inference settings. As an alternative to methods that
focus on predicting the response (or parameters) $\mathbf{y}$ from features
$\mathbf{x}$, we provide nonparametric conditional density estimation (CDE)
tools for approximating and validating the entire probability density function
(PDF) $\mathrm{p}(\mathbf{y}|\mathbf{x})$ of $\mathbf{y}$ given (i.e.,
conditional on) $\mathbf{x}$. As there is no one-size-fits-all CDE method, the
goal of this work is to provide a comprehensive range of statistical tools and
open-source software for nonparametric CDE and method assessment which can
accommodate different types of settings and be easily fit to the problem at
hand. Specifically, we introduce four CDE software packages in
$\texttt{Python}$ and $\texttt{R}$ based on ML prediction methods adapted and
optimized for CDE: $\texttt{NNKCDE}$, $\texttt{RFCDE}$, $\texttt{FlexCode}$,
and $\texttt{DeepCDE}$. Furthermore, we present the $\texttt{cdetools}$
package, which includes functions for computing a CDE loss function for tuning
and assessing the quality of individual PDFs, along with diagnostic functions.
We provide sample code in $\texttt{Python}$ and $\texttt{R}$ as well as
examples of applications to photometric redshift estimation and likelihood-free
cosmological inference via CDE. | astro-ph_IM |
Efficient generation and optimization of stochastic template banks by a
neighboring cell algorithm: Placing signal templates (grid points) as efficiently as possible to cover a
multi-dimensional parameter space is crucial in computing-intensive
matched-filtering searches for gravitational waves, but also in similar
searches in other fields of astronomy. To generate efficient coverings of
arbitrary parameter spaces, stochastic template banks have been advocated,
where templates are placed at random while rejecting those too close to others.
However, in this simple scheme, for each new random point its distance to every
template in the existing bank is computed. This rapidly increasing number of
distance computations can render the acceptance of new templates
computationally prohibitive, particularly for wide parameter spaces or in large
dimensions. This work presents a neighboring cell algorithm that can
dramatically improve the efficiency of constructing a stochastic template bank.
By dividing the parameter space into sub-volumes (cells), for an arbitrary
point an efficient hashing technique is exploited to obtain the index of its
enclosing cell along with the parameters of its neighboring templates. Hence
only distances to these neighboring templates in the bank are computed,
massively lowering the overall computing cost, as demonstrated in simple
examples. Furthermore, we propose a novel method based on this technique to
increase the fraction of covered parameter space solely by directed template
shifts, without adding any templates. As is demonstrated in examples, this
method can be highly effective.. | astro-ph_IM |
Space very long baseline interferometry in China: Space very long baseline interferometry (VLBI) has unique applications in
high-resolution imaging of fine structure of astronomical objects and
high-precision astrometry due to the key long space-Earth or space-space
baselines beyond the Earth's diameter. China has been actively involved in the
development of space VLBI in recent years. This review briefly summarizes
China's research progress in space VLBI and the future development plan. | astro-ph_IM |
A linearized approach to radial velocity extraction: High-precision radial velocity (RV) measurements are crucial for exoplanet
detection and characterisation. Efforts to achieve ~10 cm/s precision have been
made over the recent decades, with significant advancements in instrumentation,
data reduction techniques, and statistical inference methods. However, despite
these efforts, RV precision is currently limited to ~50 cm/s. This value
exceeds state-of-the-art spectrographs' expected instrumental noise floor and
is mainly attributed to RV signals induced by stellar variability. In this
work, we propose a factorisation method to overcome this limitation. The
factorisation is particularly suitable for controlling the effect of localised
changes in the stellar emission profile, assuming some smooth function of a few
astrophysical parameters governs them. We use short-time Fourier transforms
(STFT) to infer the RV in a procedure equivalent to least-squares minimisation
in the wavelength domain and demonstrate the effectiveness of our method in
treating arbitrary temperature fluctuations on the star's surface. The proposed
prescription can be naturally generalised to account for other effects, either
intrinsic to the star, such as magnetic fields, or extrinsic to it, such as
telluric contamination. As a proof-of-concept, we empirically derive a set of
factorisation terms describing the Solar centre-to-limb variation and apply
them to a set of realistic SOAP-GPU spectral simulations. We discuss the
method's capability to mitigate variability-induced RV signals and its
potential extensions to serve as a tomographic tool. | astro-ph_IM |
Estimating Extinction using Unsupervised Machine Learning: Dust extinction is the most robust tracer of the gas distribution in the
interstellar medium, but measuring extinction is limited by the systematic
uncertainties involved in estimating the intrinsic colors to background stars.
In this paper we present a new technique, PNICER, that estimates intrinsic
colors and extinction for individual stars using unsupervised machine learning
algorithms. This new method aims to be free from any priors with respect to the
column density and intrinsic color distribution. It is applicable to any
combination of parameters and works in arbitrary numbers of dimensions.
Furthermore, it is not restricted to color space. Extinction towards single
sources is determined by fitting Gaussian Mixture Models along the extinction
vector to (extinction-free) control field observations. In this way it becomes
possible to describe the extinction for observed sources with probability
densities. PNICER effectively eliminates known biases found in similar methods
and outperforms them in cases of deep observational data where the number of
background galaxies is significant, or when a large number of parameters is
used to break degeneracies in the intrinsic color distributions. This new
method remains computationally competitive, making it possible to correctly
de-redden millions of sources within a matter of seconds. With the
ever-increasing number of large-scale high-sensitivity imaging surveys, PNICER
offers a fast and reliable way to efficiently calculate extinction for
arbitrary parameter combinations without prior information on source
characteristics. PNICER also offers access to the well-established NICER
technique in a simple unified interface and is capable of building extinction
maps including the NICEST correction for cloud substructure. PNICER is offered
to the community as an open-source software solution and is entirely written in
Python. | astro-ph_IM |
Supersonic turbulence simulations with GPU-based high-order
Discontinuous Galerkin hydrodynamics: We investigate the numerical performance of a Discontinuous Galerkin (DG)
hydrodynamics implementation when applied to the problem of driven, isothermal
supersonic turbulence. While the high-order element-based spectral approach of
DG is known to efficiently produce accurate results for smooth problems
(exponential convergence with expansion order), physical discontinuities in
solutions, like shocks, prove challenging and may significantly diminish DG's
applicability to practical astrophysical applications. We consider whether DG
is able to retain its accuracy and stability for highly supersonic turbulence,
characterized by a network of shocks. We find that our new implementation,
which regularizes shocks at sub-cell resolution with artificial viscosity,
still performs well compared to standard second-order schemes for moderately
high Mach number turbulence, provided we also employ an additional projection
of the primitive variables onto the polynomial basis to regularize the
extrapolated values at cell interfaces. However, the accuracy advantage of DG
diminishes significantly in the highly supersonic regime. Nevertheless, in
turbulence simulations with a wide dynamic range that start with supersonic
Mach numbers and can resolve the sonic point, the low numerical dissipation of
DG schemes still proves advantageous in the subsonic regime. Our results thus
support the practical applicability of DG schemes for demanding astrophysical
problems that involve strong shocks and turbulence, such as star formation in
the interstellar medium. We also discuss the substantial computational cost of
DG when going to high order, which needs to be weighted against the resulting
accuracy gain. For problems containing shocks, this favours the use of
comparatively low DG order. | astro-ph_IM |
Mechanical cryocooler noise observed in the ground testing of the
Resolve X-ray microcalorimeter onboard XRISM: Low-temperature detectors often use mechanical coolers as part of the cooling
chain in order to reach sub-Kelvin operating temperatures. The microphonics
noise caused by the mechanical coolers is a general and inherent issue for
these detectors. We have observed this effect in the ground test data obtained
with the Resolve instrument to be flown on the XRISM satellite. Resolve is a
cryogenic X-ray microcalorimeter spectrometer with a required energy resolution
of 7 eV at 6 keV. Five mechanical coolers are used to cool from ambient
temperature to about 4 K: four two-stage Stirling coolers (STC) driven
nominally at 15 Hz and a Joule-Thomson cooler (JTC) driven nominally at 52 Hz.
In 2019, we operated the flight-model instrument for two weeks, in which we
also obtained accelerometer data inside the cryostat at a low-temperature stage
(He tank). X-ray detector and accelerometer data were obtained continuously
while changing the JTC drive frequency, which produced a unique data set for
investigating how the vibration from the cryocoolers propagates to the
detector. In the detector noise spectra, we observed harmonics of both STCs and
JTC. More interestingly, we also observed the low (<20 Hz) frequency beat
between the 4'th JTC and 14'th STC harmonics and the 7'th JTC and the 23--24'th
STC harmonics. We present here a description and interpretation of these
measurements. | astro-ph_IM |
Low-frequency wideband timing of InPTA pulsars observed with the uGMRT: High-precision measurements of the pulsar dispersion measure (DM) are
possible using telescopes with low-frequency wideband receivers. We present an
initial study of the application of the wideband timing technique, which can
simultaneously measure the pulsar times of arrival (ToAs) and DMs, for a set of
five pulsars observed with the upgraded Giant Metrewave Radio Telescope (uGMRT)
as part of the Indian Pulsar Timing Array (InPTA) campaign. We have used the
observations with the 300-500 MHz band of the uGMRT for this purpose. We obtain
high precision in DM measurements with precisions of the order
10^{-6}cm^{-3}pc. The ToAs obtained have sub-{\mu}s precision and the
root-mean-square of the post-fit ToA residuals are in the sub-{\mu}s range. We
find that the uncertainties in the DMs and ToAs obtained with this wideband
technique, applied to low-frequency data, are consistent with the results
obtained with traditional pulsar timing techniques and comparable to
high-frequency results from other PTAs. This work opens up an interesting
possibility of using low-frequency wideband observations for precision pulsar
timing and gravitational wave detection with similar precision as
high-frequency observations used conventionally. | astro-ph_IM |
Flexure updates to MOSFIRE on the Keck I telescope: We present a recent evaluation and updates applied to the Multi-Object
Spectrometer For Infra-Red Exploration (MOSFIRE) on the Keck I telescope. Over
the course of significantly long integrations, when MOSFIRE sits on one mask
for $>$4 hours, a slight drift in mask stars has been measured. While this does
not affect all science-cases done with MOSFIRE, the drift can smear out signal
for observers whose science objective depends upon lengthy integrations. This
effect was determined to be the possible result of three factors: the internal
flexure compensation system (FCS), the guider camera flexure system, and/or the
differential atmospheric refraction (DAR) corrections. In this work, we will
summarize the three systems and walk through the current testing done to narrow
down the possible culprit of this drift and highlight future testing to be
done. | astro-ph_IM |
First on-sky results of a FIOS prototype, a Fabry Perot Based Instrument
for Oxygen Searches: The upcoming Extremely Large Telescopes (ELTs) are expected to have the
collecting area required to detect potential biosignature gases such as
molecular oxygen, $\mathrm{O_2}$, in the atmosphere of terrestrial planets
around nearby stars. One of the most promising detection methods is
transmission spectroscopy. To maximize our capability to detect $\mathrm{O_2}$
using this method, spectral resolutions $\mathrm{R}\geq 300,000$ are required
to fully resolve the absorption lines in an Earth-like exoplanet atmosphere and
disentangle the signal from telluric lines. Current high-resolution
spectrographs typically achieve a spectral resolution of
$\mathrm{R}\sim100,000$. Increasing the resolution in seeing limited
observations/instruments requires drastically larger optical components, making
these instruments even more expensive and hard to fabricate and assemble.
Instead, we demonstrate a new approach to high-resolution spectroscopy. We
implemented an ultra-high spectral resolution booster to be coupled in front of
a high-resolution spectrograph. The instrument is based on a chained Fabry
Perot array which generates a hyperfine spectral profile. We present on-sky
telluric observations with a lab demonstrator. Depending on the configuration,
this two-arm prototype reaches a resolution of R=250,000-350,000. After
carefully modeling the prototype's behavior, we propose a Fabry Perot
Interferometer (FPI) design for an eight-arm array configuration aimed at ELTs
capable of exceeding R=300,000. The novel FPI resolution booster can be plugged
in at the front end of an existing R=100,000 spectrograph to overwrite the
spectral profile with a higher resolution for exoplanet atmosphere studies. | astro-ph_IM |
Development of Dual-Gain SiPM Boards for Extending the Energy Dynamic
Range: Astronomical observations with gamma rays in the range of several hundred keV
to hundreds of MeV currently represent the least explored energy range. To
address this so-called MeV gap, we designed and built a prototype CsI:Tl
calorimeter instrument using a commercial off-the-shelf (COTS) SiPMs and
front-ends which may serve as a subsystem for a larger gamma-ray mission
concept. During development, we observed significant non-linearity in the
energy response. Additionally, using the COTS readout, the calorimeter could
not cover the four orders of magnitude in energy range required for the
telescope. We, therefore, developed dual-gain silicon photomultiplier (SiPM)
boards that make use of two SiPM species that are read out separately to
increase the dynamic energy range of the readout. In this work, we investigate
the SiPM's response with regards to active area ($3\times3 \ \mathrm{mm}^2$ and
$1 \times 1 \ \mathrm{mm}^2$) and various microcell sizes ($10$, $20$, and $35
\ \mu \mathrm{m}$). We read out $3\times3\times6 \ \mathrm{cm}^3$ CsI:Tl chunks
using dual-gain SiPMs that utilize $35 \ \mu \mathrm{m}$ microcells for both
SiPM species and demonstrate the concept when tested with high-energy gamma-ray
and proton beams. We also studied the response of $17 \times 17 \times 100 \
\mathrm{mm}^3$ CsI bars to high-energy protons. With the COTS readout, we
demonstrate a sensitivity to $60 \ \mathrm{MeV}$ protons with the two SiPM
species overlapping at a range of around $2.5-30 \ \mathrm{MeV}$. This
development aims to demonstrate the concept for future scintillator-based
high-energy calorimeters with applications in gamma-ray astrophysics. | astro-ph_IM |
First 230 GHz VLBI Fringes on 3C 279 using the APEX Telescope: We report about a 230 GHz very long baseline interferometry (VLBI) fringe
finder observation of blazar 3C 279 with the APEX telescope in Chile, the
phased submillimeter array (SMA), and the SMT of the Arizona Radio Observatory
(ARO). We installed VLBI equipment and measured the APEX station position to 1
cm accuracy (1 sigma). We then observed 3C 279 on 2012 May 7 in a 5 hour 230
GHz VLBI track with baseline lengths of 2800 M$\lambda$ to 7200 M$\lambda$ and
a finest fringe spacing of 28.6 micro-arcseconds. Fringes were detected on all
baselines with SNRs of 12 to 55 in 420 s. The correlated flux density on the
longest baseline was ~0.3 Jy/beam, out of a total flux density of 19.8 Jy.
Visibility data suggest an emission region <38 uas in size, and at least two
components, possibly polarized. We find a lower limit of the brightness
temperature of the inner jet region of about 10^10 K. Lastly, we find an upper
limit of 20% on the linear polarization fraction at a fringe spacing of ~38
uas. With APEX the angular resolution of 230 GHz VLBI improves to 28.6 uas.
This allows one to resolve the last-photon ring around the Galactic Center
black hole event horizon, expected to be 40 uas in diameter, and probe radio
jet launching at unprecedented resolution, down to a few gravitational radii in
galaxies like M 87. To probe the structure in the inner parsecs of 3C 279 in
detail, follow-up observations with APEX and five other mm-VLBI stations have
been conducted (March 2013) and are being analyzed. | astro-ph_IM |
First observations and magnitude measurement of Starlink's Darksat: Measure the Sloan g' magnitudes of the Starlink's STARLINK-1130 (Darksat) and
1113 LEO communication satellites and determine the effectiveness of the
Darksat darkening treatment at 475.4\,nm. Two observations of the Starlink's
Darksat LEO communication satellite were conducted on 2020/02/08 and 2020/03/06
using a Sloan r' and g' filter respectively. While a second satellite,
STARLINK-1113 was observed on 2020/03/06 using a Sloan g' filter. The initial
observation on 2020/02/08 was a test observation when Darksat was still
manoeuvring to its nominal orbit and orientation. Based on the successful test
observation, the first main observation was conducted on 2020/03/06 along with
an observation of the second Starlink satellite. The calibration, image
processing and analysis of the Darksat Sloan g' image gives an estimated Sloan
g' magnitude of $7.46\pm0.04$ at a range of 976.50\,km. For STARLINK-1113 an
estimated Sloan g' magnitude of $6.59\pm0.05$ at a range of 941.62\,km was
found. When scaled to a range of 550\,km and corrected for the solar and
observer phase angles, a reduction by a factor of two is seen in the reflected
solar flux between Darksat and STARLINK-1113. The data and results presented in
this work, show that the special darkening coating used by Starlink for Darksat
has darkened the Sloan g' magnitude by $0.77\pm0.05$\,mag, when the range is
equal to a nominal orbital height (550\,km). This result will serve members of
the astronomical community modelling the satellite mega-constellations, to
ascertain their true impact on both the amateur and professional astronomical
communities. Concurrent and further observations are planned to cover the full
optical and NIR spectrum, from an ensemble of instruments, telescopes and
observatories. | astro-ph_IM |
The ROAD to discovery: machine learning-driven anomaly detection in
radio astronomy spectrograms: As radio telescopes increase in sensitivity and flexibility, so do their
complexity and data-rates. For this reason automated system health management
approaches are becoming increasingly critical to ensure nominal telescope
operations. We propose a new machine learning anomaly detection framework for
classifying both commonly occurring anomalies in radio telescopes as well as
detecting unknown rare anomalies that the system has potentially not yet seen.
To evaluate our method, we present a dataset consisting of 7050
autocorrelation-based spectrograms from the Low Frequency Array (LOFAR)
telescope and assign 10 different labels relating to the system-wide anomalies
from the perspective of telescope operators. This includes electronic failures,
miscalibration, solar storms, network and compute hardware errors among many
more. We demonstrate how a novel Self Supervised Learning (SSL) paradigm, that
utilises both context prediction and reconstruction losses, is effective in
learning normal behaviour of the LOFAR telescope. We present the Radio
Observatory Anomaly Detector (ROAD), a framework that combines both SSL-based
anomaly detection and a supervised classification, thereby enabling both
classification of both commonly occurring anomalies and detection of unseen
anomalies. We demonstrate that our system is real-time in the context of the
LOFAR data processing pipeline, requiring <1ms to process a single spectrogram.
Furthermore, ROAD obtains an anomaly detection F-2 score of 0.92 while
maintaining a false positive rate of ~2\%, as well as a mean per-class
classification F-2 score 0.89, outperforming other related works. | astro-ph_IM |
Effects of the Hunga Tonga-Hunga Ha'apai Volcanic Eruption on
Observations at Paranal Observatory: The Hunga Tonga-Hunga Ha'apai volcano erupted on 15 January 2022 with an
energy equivalent to around 61 megatons of TNT. The explosion was bigger than
any other volcanic eruption so far in the 21st century. Huge quantities of
particles, including dust and water vapour, were released into the atmosphere.
We present the results of a preliminary study of the effects of the explosion
on observations taken at Paranal Observatory using a range of instruments.
These effects were not immediately transitory in nature, and a year later
stunning sunsets are still being seen at Paranal. | astro-ph_IM |
A Constrained Transport Scheme for MHD on Unstructured Static and Moving
Meshes: Magnetic fields play an important role in many astrophysical systems and a
detailed understanding of their impact on the gas dynamics requires robust
numerical simulations. Here we present a new method to evolve the ideal
magnetohydrodynamic (MHD) equations on unstructured static and moving meshes
that preserves the magnetic field divergence-free constraint to machine
precision. The method overcomes the major problems of using a cleaning scheme
on the magnetic fields instead, which is non-conservative, not fully Galilean
invariant, does not eliminate divergence errors completely, and may produce
incorrect jumps across shocks. Our new method is a generalization of the
constrained transport (CT) algorithm used to enforce the $\nabla\cdot
\mathbf{B}=0$ condition on fixed Cartesian grids. Preserving $\nabla\cdot
\mathbf{B}=0$ at the discretized level is necessary to maintain the
orthogonality between the Lorentz force and $\mathbf{B}$. The possibility of
performing CT on a moving mesh provides several advantages over static mesh
methods due to the quasi-Lagrangian nature of the former (i.e., the mesh
generating points move with the flow), such as making the simulation
automatically adaptive and significantly reducing advection errors. Our method
preserves magnetic fields and fluid quantities in pure advection exactly. | astro-ph_IM |
Optical Cross Correlation Filters: An Economical Approach for
Identifying SNe Ia and Estimating their Redshifts: Large photometric surveys of transient phenomena, such as Pan-STARRS and
LSST, will locate thousands to millions of type Ia supernova candidates per
year, a rate prohibitive for acquiring spectroscopy to determine each
candidate's type and redshift. In response, we have developed an economical
approach to identifying SNe Ia and their redshifts using an uncommon type of
optical filter which has multiple, discontinuous passbands on a single
substrate. Observation of a supernova through a specially designed pair of
these `cross-correlation filters' measures the approximate amplitude and phase
of the cross-correlation between the spectrum and a SN Ia template, a quantity
typically used to determine the redshift and type of a high-redshift SN Ia.
Simulating the use of these filters, we obtain a sample of SNe Ia which is ~98%
pure with individual redshifts measured to 0.01 precision. The advantages of
this approach over standard broadband photometric methods are that it is
insensitive to reddening, independent of the color data used for subsequent
distance determinations which reduces selection or interpretation bias, and
because it makes use of the spectral features its reliability is greater. A
great advantage over long-slit spectroscopy comes from increased throughput,
enhanced multiplexing and reduced set-up time resulting in a net gain in speed
of up to ~30 times. This approach is also insensitive to host galaxy
contamination. Prototype filters were built and successfully used on Magellan
with LDSS-3 to characterize three SNLS candidates. We discuss how these filters
can provide critical information for the upcoming photometric supernova
surveys. | astro-ph_IM |
Autocollimating compensator for controlling aspheric optical surfaces: A compensator (null-corrector) for testing aspheric optical surfaces is
proposed, which enables i) independent verification of optical elements and
assembling of the compensator itself, and ii) ascertaining the compensator
position in a control layout for a specified aspheric surface. The compensator
consists of three spherical lenses made of the same glass. In this paper, the
scope of the compensator expanded to a surface speed ~f/2.3; a conceptual
example for a nominal primary of Hubble Space Telescope is given. The
autocollimating design allows significant reducing difficulties associated with
practical use of lens compensators. | astro-ph_IM |
An optimized algorithm for multi-scale wideband deconvolution of radio
astronomical images: We describe a new multi-scale deconvolution algorithm that can also be used
in multi-frequency mode. The algorithm only affects the minor clean loop. In
single-frequency mode, the minor loop of our improved multi-scale algorithm is
over an order of magnitude faster than the CASA multi-scale algorithm, and
produces results of similar quality. For multi-frequency deconvolution, a
technique named joined-channel cleaning is used. In this mode, the minor loop
of our algorithm is 2-3 orders of magnitude faster than CASA MSMFS. We extend
the multi-scale mode with automated scale-dependent masking, which allows
structures to be cleaned below the noise. We describe a new scale-bias function
for use in multi-scale cleaning. We test a second deconvolution method that is
a variant of the MORESANE deconvolution technique, and uses a convex
optimisation technique with isotropic undecimated wavelets as dictionary. On
simple, well calibrated data the convex optimisation algorithm produces
visually more representative models. On complex or imperfect data, the convex
optimisation algorithm has stability issues. | astro-ph_IM |
An Overview of CHIME, the Canadian Hydrogen Intensity Mapping Experiment: The Canadian Hydrogen Intensity Mapping Experiment (CHIME) is a drift scan
radio telescope operating across the 400-800 MHz band. CHIME is located at the
Dominion Radio Astrophysical Observatory near Penticton, BC Canada. The
instrument is designed to map neutral hydrogen over the redshift range 0.8 to
2.5 to constrain the expansion history of the Universe. This goal drives the
design features of the instrument. CHIME consists of four parallel cylindrical
reflectors, oriented north-south, each 100 m $\times$ 20 m and outfitted with a
256 element dual-polarization linear feed array. CHIME observes a two degree
wide stripe covering the entire meridian at any given moment, observing 3/4 of
the sky every day due to Earth rotation. An FX correlator utilizes FPGAs and
GPUs to digitize and correlate the signals, with different correlation products
generated for cosmological, fast radio burst, pulsar, VLBI, and 21 cm absorber
backends. For the cosmology backend, the $N_\mathrm{feed}^2$ correlation matrix
is formed for 1024 frequency channels across the band every 31 ms. A data
receiver system applies calibration and flagging and, for our primary
cosmological data product, stacks redundant baselines and integrates for 10 s.
We present an overview of the instrument, its performance metrics based on the
first three years of science data, and we describe the current progress in
characterizing CHIME's primary beam response. We also present maps of the sky
derived from CHIME data; we are using versions of these maps for a cosmological
stacking analysis as well as for investigation of Galactic foregrounds. | astro-ph_IM |
The JEM-EUSO Mission: Contributions to the ICRC 2013: Contributions of the JEM-EUSO Collaboration to the 33rd International Cosmic
Ray Conference (The Astroparticle Physics Conference) Rio de Janeiro, July,
2013. | astro-ph_IM |
Data mining techniques on astronomical spectra data. I : Clustering
Analysis: Clustering is an effective tool for astronomical spectral analysis, to mine
clustering patterns among data. With the implementation of large sky surveys,
many clustering methods have been applied to tackle spectroscopic and
photometric data effectively and automatically. Meanwhile, the performance of
clustering methods under different data characteristics varies greatly. With
the aim of summarizing astronomical spectral clustering algorithms and laying
the foundation for further research, this work gives a review of clustering
methods applied to astronomical spectra data in three parts. First, many
clustering methods for astronomical spectra are investigated and analysed
theoretically, looking at algorithmic ideas, applications, and features.
Secondly, experiments are carried out on unified datasets constructed using
three criteria (spectra data type, spectra quality, and data volume) to compare
the performance of typical algorithms; spectra data are selected from the Large
Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST) survey and Sloan
Digital Sky Survey (SDSS). Finally, source codes of the comparison clustering
algorithms and manuals for usage and improvement are provided on GitHub. | astro-ph_IM |
Advanced Kelvin Probe Operational Methodology for Space Applications: We present a novel methodology for the operation of macroscopic Kelvin Probe
instruments. The methodology is based on the use of a harmonic backing
potential signal to drive the tip-sample variable capacitance and on a Fourier
representation of the tip current, allows for the operation of the instrument
under full control and improves its scanning performance by a factor of 60 or
more over that of currently available commercial instruments. | astro-ph_IM |
Improvements to the Search for Cosmic Dawn Using the Long Wavelength
Array: We present recent improvements to the search for the global Cosmic Dawn
signature using the Long Wavelength Array station located on the Sevilleta
National Wildlife Refuge in New Mexico, USA (LWA-SV). These improvements are
both in the methodology of the experiment and the hardware of the station. An
improved observing strategy along with more sophisticated temperature
calibration and foreground modelling schemes have led to improved residual RMS
limits. A large improvement over previous work using LWA-SV is the use of a
novel achromatic beamforming technique which has been developed for LWA-SV. We
present results from an observing campaign which contains 29 days of
observations between March $10^{\rm{th}}$, 2021 and April $10^{\rm{th}}$ 2021.
The reported residual RMS limits are 6 times above the amplitude of the
potential signal reported by the Experiment to Detect the Global EoR Signature
(EDGES) collaboration. | astro-ph_IM |
Effects of $150-1000$ eV Electron Impacts on Pure Carbon Monoxide Ices
using the Interstellar Energetic-Process System (IEPS): Pure CO ice has been irradiated with electrons of energy in the range
$150-1000$~eV with the Interstellar Energetic-Process System (IEPS). The main
products of irradiation are carbon chains C$_n$ ($n=3$, 5, 6, 8, 9, 10, 11,
12), suboxides, C$_n$O ($n=2$, 3, 4, 5, 6, 7), and C$_n$O$_2$ ($n=1$, 3, 4, 5,
7) species. \ce{CO2} is by far the most abundant reaction product in all the
experiments. The destruction cross-section of CO peaks at about 250 eV,
decreases with the energy of the electrons and is more than one order of
magnitude higher than for gas-phase CO ionization. The production cross-section
of carbon dioxide has been also derived and is characterized by the competition
between chemistry and desorption.
Desorption of CO and of new species during the radiolysis follows the
electron distribution in the ice. Low energy electrons having short penetration
depths induce significant desorption. Finally, as the ice thickness approaches
the electron penetration depth the abundance of the products starts to
saturate. Implications on the atmospheric photochemistry of cold planets
hosting surface CO ices are also discussed. | astro-ph_IM |
Bayesian inference for pulsar timing models: The extremely regular, periodic radio emission from millisecond pulsars makes
them useful tools for studying neutron star astrophysics, general relativity,
and low-frequency gravitational waves. These studies require that the observed
pulse times of arrival be fit to complex timing models that describe numerous
effects such as the astrometry of the source, the evolution of the pulsar's
spin, the presence of a binary companion, and the propagation of the pulses
through the interstellar medium. In this paper, we discuss the benefits of
using Bayesian inference to obtain pulsar timing solutions. These benefits
include the validation of linearized least-squares model fits when they are
correct, and the proper characterization of parameter uncertainties when they
are not; the incorporation of prior parameter information and of models of
correlated noise; and the Bayesian comparison of alternative timing models. We
describe our computational setup, which combines the timing models of Tempo2
with the nested-sampling integrator MultiNest. We compare the timing solutions
generated using Bayesian inference and linearized least-squares for three
pulsars: B1953+29, J2317+1439, and J1640+2224, which demonstrate a variety of
the benefits that we posit. | astro-ph_IM |
VOEvent Standard for Fast Radio Bursts: Fast radio bursts are a new class of transient radio phenomena currently
detected as millisecond radio pulses with very high dispersion measures. As new
radio surveys begin searching for FRBs a large population is expected to be
detected in real-time, triggering a range of multi-wavelength and
multi-messenger telescopes to search for repeating bursts and/or associated
emission. Here we propose a method for disseminating FRB triggers using Virtual
Observatory Events (VOEvents). This format was developed and is used
successfully for transient alerts across the electromagnetic spectrum and for
multi-messenger signals such as gravitational waves. In this paper we outline a
proposed VOEvent standard for FRBs that includes the essential parameters of
the event and where these parameters should be specified within the structure
of the event. An additional advantage to the use of VOEvents for FRBs is that
the events can automatically be ingested into the FRB Catalogue (FRBCAT)
enabling real-time updates for public use. We welcome feedback from the
community on the proposed standard outlined below and encourage those
interested to join the nascent working group forming around this topic. | astro-ph_IM |
Study on the gain and photon detection efficiency drops of silicon
photomultipliers under bright background conditions: The use of silicon photomultipliers (SiPMs) in imaging atmospheric Cherenkov
telescopes is expected to extend the observation times of very-high-energy
gamma-ray sources, particularly within the highest energy domain of 50-300 TeV,
where the Cherenkov signal from celestial gamma rays is adequate even under
bright moonlight background conditions. Unlike conventional photomultiplier
tubes, SiPMs do not exhibit quantum efficiency or gain degradation, which can
be observed after long exposures to bright illumination. However, under bright
conditions, the photon detection efficiency of a SiPM can be undergo temporary
degradation because a fraction of its avalanche photodiode cells can saturate
owing to photons from the night-sky background (NSB). In addition, the large
current generated by the high NSB rate can increase the temperature of the
silicon substrate, resulting in shifts in the SiPM breakdown voltages and
consequent gain changes. Moreover, this large current changes the effective
bias voltage because it causes a voltage drop across the protection resistor of
100-1000 {\Omega}. Hence, these three factors, namely the avalanche photodiode
(APD) saturation, Si temperature, and voltage drop must be carefully
compensated for and/or considered in the energy calibration of Cherenkov
telescopes with SiPM cameras. In this study, we measured the signal output
charge of a SiPM and its variation as a function of different NSB-like
background conditions up to 1 GHz/pixel. The results verify that the product of
the SiPM gain and photon detection efficiency is well characterized by these
three factors. | astro-ph_IM |
Evolution of Data Formats in Very-High-Energy Gamma-ray Astronomy: Most major scientific results produced by ground-based gamma-ray telescopes
in the last 30 years have been obtained by expert members of the collaborations
operating these instruments. This is due to the proprietary data and software
policies adopted by these collaborations. However, the advent of the next
generation of telescopes and their operation as observatories open to the
astronomical community, along with a generally increasing demand for open
science, confront gamma-ray astronomers with the challenge of sharing their
data and analysis tools. As a consequence, in the last few years, the
development of open-source science tools has progressed in parallel with the
endeavour to define a standardised data format for astronomical gamma-ray data.
The latter constitutes the main topic of this review. Common data
specifications provide equally important benefits to the current and future
generation of gamma-ray instruments: they allow the data from different
instruments, including legacy data from decommissioned telescopes, to be easily
combined and analysed within the same software framework. In addition,
standardised data accessible to the public, and analysable with open-source
software, grant fully-reproducible results. In this article we provide an
overview of the evolution of the data format for gamma-ray astronomical data,
focusing on its progression from private and diverse specifications to
prototypical open and standardised ones. The latter have already been
successfully employed in a number of publications paving the way to the
analysis of data from the next generation of gamma-ray instruments, and to an
open and reproducible way of conducting gamma-ray astronomy. | astro-ph_IM |
Perspectives on Reproducibility and Sustainability of Open-Source
Scientific Software from Seven Years of the Dedalus Project: As the Science Mission Directorate contemplates establishing an open code
policy, we consider it timely to share our experiences as the developers of the
open-source partial differential equation solver Dedalus. Dedalus is a flexible
framework for solving partial differential equations. Its development team
primarily uses it for studying stellar and planetary astrophysics. Dedalus was
developed originally for astrophysical fluid dynamics (AFD), though it has
found a much broader user base, including applied mathematicians, plasma
physicists, and oceanographers. Here, we will focus on issues related to
open-source software from the perspective of AFD. We use the term AFD with the
understanding that astrophysics simulations are inherently multi-physics: fluid
dynamics coupled with some combination of gravitational dynamics, radiation
transfer, relativity, and magnetic fields. In practice, a few well-known
open-source simulation packages represent a large fraction of published work in
the field. However, we will argue that an open-code policy should encompass not
just these large simulation codes, but also the input files and analysis
scripts. It is our interest that NASA adopt an open-code policy because without
it, reproducibility in computational science is needlessly hampered. | astro-ph_IM |
A broadband scalar optical vortex coronagraph: In recent years, new coronagraphic schemes have been proposed, the most
promising being the optical vortex phase mask coronagraphs. In our work, a new
scheme of broadband optical scalar vortex coronagraph is proposed and
characterized experimentally in the laboratory. Our setup employs a pair of
computer generated phase gratings (one of them containing a singularity) to
control the chromatic dispersion of phase plates and achieves a constant
peak-to-peak attenuation below 1:1000 over a bandwidth of 120 nm centered at
700 nm. An inner working angle of $\lambda$/D is demonstrated along with a raw
contrast of 11.5\,magnitudes at 2$\lambda$/D. A more compact setup achieves a
peak-to-peak attenuation below 1:1000 over a bandwidth of 60 nm with the other
results remaining the same. | astro-ph_IM |
The LOFAR View of Cosmic Magnetism: The origin of magnetic fields in the Universe is an open problem in
astrophysics and fundamental physics. Polarization observations with the
forthcoming large radio telescopes will open a new era in the observation of
magnetic fields and should help to understand their origin. At low frequencies,
LOFAR (10-240 MHz) will allow us to map the structure of weak magnetic fields
in the outer regions and halos of galaxies, in galaxy clusters and in the Milky
Way via their synchrotron emission. Even weaker magnetic fields can be measured
at low frequencies with help of Faraday rotation measures. A detailed view of
the magnetic fields in the local Milky Way will be derived by Faraday rotation
measures from pulsars. First promising images with LOFAR have been obtained for
the Crab pulsar-wind nebula, the spiral galaxy M51, the radio galaxy M87 and
the galaxy clusters A2255 and A2256. With help of the polarimetric technique of
"Rotation Measure Synthesis", diffuse polarized emission has been detected from
a magnetic bubble in the local Milky Way. Polarized emission and rotation
measures were measured for more than 20 pulsars so far. | astro-ph_IM |
Optimal PSF modeling for weak lensing: complexity and sparsity: We investigate the impact of point spread function (PSF) fitting errors on
cosmic shear measurements using the concepts of complexity and sparsity.
Complexity, introduced in a previous paper, characterizes the number of degrees
of freedom of the PSF. For instance, fitting an underlying PSF with a model
with low complexity will lead to small statistical errors on the model
parameters, however these parameters could suffer from large biases.
Alternatively, fitting with a large number of parameters will tend to reduce
biases at the expense of statistical errors. We perform an optimisation of
scatters and biases by studying the mean squared error of a PSF model. We also
characterize a model sparsity, which describes how efficiently the model is
able to represent the underlying PSF using a limited number of free parameters.
We present the general case and illustrate it for a realistic example of PSF
fitted with shapelet basis sets. We derive the relation between complexity and
sparsity of the PSF model, signal-to-noise ratio of stars and systematic errors
on cosmological parameters. With the constraint of maintaining the systematics
below the statistical uncertainties, this lead to a relation between the
required number of stars to calibrate the PSF and the sparsity. We discuss the
impact of our results for current and future cosmic shear surveys. In the
typical case where the biases can be represented as a power law of the
complexity, we show that current weak lensing surveys can calibrate the PSF
with few stars, while future surveys will require hard constraints on the
sparsity in order to calibrate the PSF with 50 stars. | astro-ph_IM |
Design and performance of a Collimated Beam Projector for telescope
transmission measurement using a broadband light source: Type Ia supernovae are the most direct cosmological probe to study dark
energy in the recent Universe, for which the photometric calibration of
astronomical instruments remains one major source of systematic uncertainties.
To address this, recent advancements introduce Collimated Beam Projectors
(CBP), aiming to enhance calibration by precisely measuring a telescope's
throughput as a function of wavelength. This work describes the performance of
a prototype portable CBP. The experimental setup consists of a broadband Xenon
light source replacing a more customary but much more demanding high-power
laser source, coupled with a monochromator emitting light inside an integrating
sphere monitored with a photodiode and a spectrograph. Light is injected at the
focus of the CBP telescope projecting a collimated beam onto a solar cell whose
quantum efficiency has been obtained by comparison with a NIST-calibrated
photodiode. The throughput and signal-to-noise ratio achieved by comparing the
photocurrent signal in the CBP photodiode to the one in the solar cell are
computed. We prove that the prototype, in its current state of development, is
capable of achieving 1.2 per cent and 2.3 per cent precision on the integrated
g and r bands of the ZTF photometric filter system respectively, in a
reasonable amount of integration time. Central wavelength determination
accuracy is kept below $\sim$ {0.91} nm and $\sim$ {0.58} nm for g and r bands.
The expected photometric uncertainty caused by filter throughput measurement is
approximately 5 mmag on the zero-point magnitude. Several straightforward
improvement paths are discussed to upgrade the current setup. | astro-ph_IM |
Gravitational Waves from Orphan Memory: Gravitational-wave memory manifests as a permanent distortion of an idealized
gravitational-wave detector and arises generically from energetic astrophysical
events. For example, binary black hole mergers are expected to emit memory
bursts a little more than an order of magnitude smaller in strain than the
oscillatory parent waves. We introduce the concept of "orphan memory":
gravitational-wave memory for which there is no detectable parent signal. In
particular, high-frequency gravitational-wave bursts ($\gtrsim$ kHz) produce
orphan memory in the LIGO/Virgo band. We show that Advanced LIGO measurements
can place stringent limits on the existence of high-frequency gravitational
waves, effectively increasing the LIGO bandwidth by orders of magnitude. We
investigate the prospects for and implications of future searches for orphan
memory. | astro-ph_IM |
The Lexington Benchmarks for Numerical Simulations of Nebulae: We present the results of a meeting on numerical simulations of ionized
nebulae held at the University of Kentucky in conjunction with the celebration
of the 70th birthdays of Profs. Donald Osterbrock and Michael Seaton. | astro-ph_IM |
The KaVA and KVN Pulsar Project: We present our work towards using the Korean VLBI (Very Long Baseline
Interferometer) Network (KVN) and VLBI Exploration of Radio Astronomy (VERA)
arrays combined into the KVN and VERA Array (KaVA) for observations of radio
pulsars at high frequencies ($\simeq$22-GHz). Pulsar astronomy is generally
focused at frequencies approximately 0.3 to several GHz and pulsars are usually
discovered and monitored with large, single-dish, radio telescopes. For most
pulsars, reduced radio flux is expected at high frequencies due to their steep
spectrum, but there are exceptions where high frequency observations can be
useful. Moreover, some pulsars are observable at high frequencies only, such as
those close to the Galactic Center. The discoveries of a radio-bright magnetar
and a few dozen extended Chandra sources within 15 arc-minute of the Galactic
Center provide strong motivations to make use of the KaVA frequency band for
searching pulsars in this region. Here, we describe the science targets and
report progresses made from the KVN test observations for known pulsars. We
then discuss why KaVA pulsar observations are compelling. | astro-ph_IM |
Separating the EoR Signal with a Convolutional Denoising Autoencoder: A
Deep-learning-based Method: When applying the foreground removal methods to uncover the faint
cosmological signal from the epoch of reionization (EoR), the foreground
spectra are assumed to be smooth. However, this assumption can be seriously
violated in practice since the unresolved or mis-subtracted foreground sources,
which are further complicated by the frequency-dependent beam effects of
interferometers, will generate significant fluctuations along the frequency
dimension. To address this issue, we propose a novel deep-learning-based method
that uses a 9-layer convolutional denoising autoencoder (CDAE) to separate the
EoR signal. After being trained on the SKA images simulated with realistic beam
effects, the CDAE achieves excellent performance as the mean correlation
coefficient ($\bar{\rho}$) between the reconstructed and input EoR signals
reaches $0.929 \pm 0.045$. In comparison, the two representative traditional
methods, namely the polynomial fitting method and the continuous wavelet
transform method, both have difficulties in modelling and removing the
foreground emission complicated with the beam effects, yielding only
$\bar{\rho}_{\text{poly}} = 0.296 \pm 0.121$ and $\bar{\rho}_{\text{cwt}} =
0.198 \pm 0.160$, respectively. We conclude that, by hierarchically learning
sophisticated features through multiple convolutional layers, the CDAE is a
powerful tool that can be used to overcome the complicated beam effects and
accurately separate the EoR signal. Our results also exhibit the great
potential of deep-learning-based methods in future EoR experiments. | astro-ph_IM |
The Signal-to-Noise Ratio for Photon Counting After Photometric
Corrections: Photon counting is a mode of processing astronomical observations of
low-signal targets that have been observed using an electron-multiplying
charge-coupled device (EMCCD). In photon counting, the EMCCD amplifies the
signal, and a thresholding technique effectively selects for the signal
electrons while drastically reducing relative noise sources. Photometric
corrections have been developed which result in the extraction of a more
accurate estimate of the signal of electrons, and the Nancy Grace Roman
Telescope will utilize a theoretical expression for the signal-to-noise ratio
(SNR) given these corrections based on well-calibrated noise parameters to plan
observations taken by its coronagraph instrument. I derive here analytic
expressions for the SNR for the method of photon counting, before and after
these photometric corrections have been applied. | astro-ph_IM |
Multi-Chroic Feed-Horn Coupled TES Polarimeters: Multi-chroic polarization sensitive detectors offer an avenue to increase
both the spectral coverage and sensitivity of instruments optimized for
observations of the cosmic-microwave background (CMB) or sub-mm sky. We report
on an effort to adapt the Truce Collaboration horn coupled bolometric
polarimeters for operation over octave bandwidth. Development is focused on
detectors operating in both the 90 and 150 GHz bands which offer the highest
CMB polarization to foreground ratio. We plan to deploy an array of 256
multi-chroic 90/150 GHz polarimeters with 1024 TES detectors on ACTPol in 2013,
and there are proposals to use this technology for balloon-borne instruments.
The combination of excellent control of beam systematics and sensitivity make
this technology ideal for future ground, ballon, and space missions. | astro-ph_IM |
fastRESOLVE: fast Bayesian imaging for aperture synthesis in radio
astronomy: The standard imaging algorithm for interferometric radio data, CLEAN, is
optimal for point source observations, but suboptimal for diffuse emission.
Recently, RESOLVE, a new Bayesian algorithm has been developed, which is ideal
for extended source imaging. Unfortunately, RESOLVE is computationally very
expensive. In this paper we present fastRESOLVE, a modification of RESOLVE
based on an approximation of the interferometric likelihood that allows us to
avoid expensive gridding routines and consequently gain a factor of roughly 100
in computation time. Furthermore, we include a Bayesian estimation of the
measurement uncertainty of the visibilities into the imaging, a procedure not
applied in aperture synthesis before. The algorithm requires little to no user
input compared to the standard method CLEAN while being superior for extended
and faint emission. We apply the algorithm to VLA data of Abell 2199 and show
that it resolves more detailed structures. | astro-ph_IM |
Atacama Compact Array Correlator for Atacama Large
Millimeter/submillimeter Array: We have developed a FX-architecture digital spectro-correlator, Atacama
Compact Array Correlator for the Atacama Large Millimeter/submillimeter Array.
The ACA Correlator processes four pairs of dual polarization signals, whose
bandwidth is 2 GHz, from up to sixteen antennas, and calculates auto- and
cross-correlation spectra including cross-polarization in all combinations of
sixteen antennas. We report the detailed design of the correlator and the
verification results of the correlator hardware. | astro-ph_IM |
The Pégase.3 code of spectrochemical evolution of galaxies:
documentation and complements: P\'egase.3 is a Fortran 95 code modeling the spectral evolution of galaxies
from the far-ultraviolet to submillimeter wavelengths. It also follows the
chemical evolution of their stars, gas and dust.
For a given scenario (a set of parameters defining the history of mass
assembly, the star formation law, the initial mass function...), P\'egase.3
consistently computes the following:
* the star formation, infall, outflow and supernova rates from 0 to 20 Gyr;
* the stellar metallicity, the abundances of main elements in the gas and the
composition of dust;
* the unattenuated stellar spectral energy distribution (SED);
* the nebular SED, using nebular continua and emission lines precomputed with
code Cloudy (Ferland et al. 2017);
* the attenuation in star-forming clouds and the diffuse interstellar medium,
by absorption and scattering on dust grains, of the stellar and nebular SEDs.
For this, the code uses grids of the transmittance for spiral and spheroidal
galaxies. We precomputed these grids through Monte Carlo simulations of
radiative transfer based on the method of virtual interactions;
* the re-emission by grains of the light they absorbed, taking into account
stochastic heating.
The main innovation compared to P\'egase.2 is the modeling of dust emission
and its evolution. The computation of nebular emission has also been entirely
upgraded to take into account metallicity effects and infrared lines.
Other major differences are that complex scenarios of evolution (derived for
instance from cosmological simulations), with several episodes of star
formation, infall or outflow, may now be implemented, and that the detailed
evolution of the most important elements -- not only the overall metallicity --
is followed. | astro-ph_IM |
On-sky performance of the SPT-3G frequency-domain multiplexed readout: Frequency-domain multiplexing (fMux) is an established technique for the
readout of large arrays of transition edge sensor (TES) bolometers. Each TES in
a multiplexing module has a unique AC voltage bias that is selected by a
resonant filter. This scheme enables the operation and readout of multiple
bolometers on a single pair of wires, reducing thermal loading onto sub-Kelvin
stages. The current receiver on the South Pole Telescope, SPT-3G, uses a 68x
fMux system to operate its large-format camera of $\sim$16,000 TES bolometers.
We present here the successful implementation and performance of the SPT-3G
readout as measured on-sky. Characterization of the noise reveals a median
pair-differenced 1/f knee frequency of 33 mHz, indicating that low-frequency
noise in the readout will not limit SPT-3G's measurements of sky power on large
angular scales. Measurements also show that the median readout white noise
level in each of the SPT-3G observing bands is below the expectation for photon
noise, demonstrating that SPT-3G is operating in the photon-noise-dominated
regime. | astro-ph_IM |
Pre-flight integration and characterization of the SPIDER balloon-borne
telescope: We present the results of integration and characterization of the SPIDER
instrument after the 2013 pre-flight campaign. SPIDER is a balloon-borne
polarimeter designed to probe the primordial gravitational wave signal in the
degree-scale $B$-mode polarization of the cosmic microwave background. With six
independent telescopes housing over 2000 detectors in the 94 GHz and 150 GHz
frequency bands, SPIDER will map 7.5% of the sky with a depth of 11 to 14
$\mu$K$\cdot$arcmin at each frequency, which is a factor of $\sim$5 improvement
over Planck. We discuss the integration of the pointing, cryogenic,
electronics, and power sub-systems, as well as pre-flight characterization of
the detectors and optical systems. SPIDER is well prepared for a December 2014
flight from Antarctica, and is expected to be limited by astrophysical
foreground emission, and not instrumental sensitivity, over the survey region. | astro-ph_IM |
BICEP3: a 95 GHz refracting telescope for degree-scale CMB polarization: BICEP3 is a 550 mm-aperture refracting telescope for polarimetry of radiation
in the cosmic microwave background at 95 GHz. It adopts the methodology of
BICEP1, BICEP2 and the Keck Array experiments - it possesses sufficient
resolution to search for signatures of the inflation-induced cosmic
gravitational-wave background while utilizing a compact design for ease of
construction and to facilitate the characterization and mitigation of
systematics. However, BICEP3 represents a significant breakthrough in
per-receiver sensitivity, with a focal plane area 5$\times$ larger than a
BICEP2/Keck Array receiver and faster optics ($f/1.6$ vs. $f/2.4$).
Large-aperture infrared-reflective metal-mesh filters and infrared-absorptive
cold alumina filters and lenses were developed and implemented for its optics.
The camera consists of 1280 dual-polarization pixels; each is a pair of
orthogonal antenna arrays coupled to transition-edge sensor bolometers and read
out by multiplexed SQUIDs. Upon deployment at the South Pole during the 2014-15
season, BICEP3 will have survey speed comparable to Keck Array 150 GHz (2013),
and will significantly enhance spectral separation of primordial B-mode power
from that of possible galactic dust contamination in the BICEP2 observation
patch. | astro-ph_IM |
The optimization of satellite orbit for Space-VLBI observation: By sending one or more telescopes into space, Space-VLBI (SVLBI) is able to
achieve even higher angular resolution and is therefore the trend of the VLBI
technique. For SVLBI program, the design of satellite orbits plays an important
role for the success of planned observation. In this paper, we present our
orbit optimization scheme, so as to facilitate the design of satellite orbit
for SVLBI observation. To achieve that, we characterize the $uv$ coverage with
a measure index and minimize it by finding out the corresponding orbit
configuration. In this way, the design of satellite orbit is converted to an
optimization problem. We can prove that, with appropriate global minimization
method, the best orbit configuration can be found within the reasonable time.
Besides that, we demonstrate this scheme can be used for the scheduling of
SVLBI observations. | astro-ph_IM |
HIDE & SEEK: End-to-End Packages to Simulate and Process Radio Survey
Data: As several large single-dish radio surveys begin operation within the coming
decade, a wealth of radio data will become available and provide a new window
to the Universe. In order to fully exploit the potential of these data sets, it
is important to understand the systematic effects associated with the
instrument and the analysis pipeline. A common approach to tackle this is to
forward-model the entire system - from the hardware to the analysis of the data
products. For this purpose, we introduce two newly developed, open-source
Python packages: the HI Data Emulator (HIDE) and the Signal Extraction and
Emission Kartographer (SEEK) for simulating and processing single-dish radio
survey data. HIDE forward-models the process of collecting astronomical radio
signals in a single-dish radio telescope instrument and outputs pixel-level
time-ordered-data. SEEK processes the time-ordered-data, removes artifacts from
Radio Frequency Interference (RFI), automatically applies flux calibration, and
aims to recover the astronomical radio signal. The two packages can be used
separately or together depending on the application. Their modular and flexible
nature allows easy adaptation to other instruments and data sets. We describe
the basic architecture of the two packages and examine in detail the noise and
RFI modeling in HIDE, as well as the implementation of gain calibration and RFI
mitigation in SEEK. We then apply HIDE & SEEK to forward-model a Galactic
survey in the frequency range 990 - 1260 MHz based on data taken at the Bleien
Observatory. For this survey, we expect to cover 70% of the full sky and
achieve a median signal-to-noise ratio of approximately 5 - 6 in the cleanest
channels including systematic uncertainties. However, we also point out the
potential challenges of high RFI contamination and baseline removal when
examining the early data from the Bleien Observatory. | astro-ph_IM |
An Extension of the Athena++ Framework for Fully Conservative
Self-Gravitating Hydrodynamics: Numerical simulations of self-gravitating flows evolve a momentum equation
and an energy equation that account for accelerations and gravitational energy
releases due to a time-dependent gravitational potential. In this work, we
implement a fully conservative numerical algorithm for self-gravitating flows,
using source terms, in the astrophysical magnetohydrodynamics framework
Athena++. We demonstrate that properly evaluated source terms are conservative
when they are equivalent to the divergence of a corresponding "gravity flux"
(i.e., a gravitational stress tensor or a gravitational energy flux). We
provide test problems that demonstrate several advantages of the
source-term-based algorithm, including second order convergence and round-off
error total momentum and total energy conservation. The fully conservative
scheme suppresses anomalous accelerations that arise when applying a common
numerical discretization of the gravitational stress tensor that does not
guarantee curl-free gravity. | astro-ph_IM |
Performance of multi-detector hybrid statistic in targeted compact
binary coalescence search: In this paper we compare the performance of two likelihood ratio based
detection statistics namely maximum likelihood ratio statistic and {\it hybrid}
statistic designed for the detection of gravitational waves from compact binary
coalescence using multiple interferometric detector networks. We perform
simulations with non-spinning double neutron star binary system and neutron
star-black hole binary systems with spinning as well as non-spinning black hole
component masses. The binary injections are distributed uniformly in volume up
to 1 Gpc. We observe that, on average, the maximum likelihood ratio statistic
recovers $\sim 34.45\%$, $\sim 49.69\%$, $\sim 61.25\%$ and $\sim 69.67\%$ of
injections in 2, 3, 4 and 5 detector networks respectively in the case of
neutron star-black hole injections for a fixed false alarm probability of
$10^{-7}$ in Gaussian noise. Further, we note that, compared to the maximum
likelihood ratio statistic, the {\it hybrid} statistic recovers $\sim 7.45\%$,
$\sim 4.57\%$, $\sim 2.56\%$ and $\sim 1.22\%$ more injections in 2, 3, 4 and 5
detector networks respectively for the same false alarm probability in Gaussian
noise. On the other hand, among binary neutron star injections, the maximum
likelihood ratio statistic recovers $\sim 5.587\%$, $\sim 9.917\%$, $\sim
14.73\%$ and $\sim 19.86\%$ of injections in 2, 3, 4 and 5 detector networks
respectively and the {\it hybrid} statistic recovers $\sim 14.63\%$, $\sim
12.91\%$, $\sim 11.49\%$ and $\sim 10.29\%$ more injections compared to maximum
likelihood ratio statistic in 2, 3, 4 and 5 detector networks respectively. | astro-ph_IM |
A Joint Roman Space Telescope and Rubin Observatory Synthetic Wide-Field
Imaging Survey: We present and validate 20 deg$^2$ of overlapping synthetic imaging surveys
representing the full depth of the Nancy Grace Roman Space Telescope
High-Latitude Imaging Survey (HLIS) and five years of observations of the Vera
C. Rubin Observatory Legacy Survey of Space and Time (LSST). The two synthetic
surveys are summarized, with reference to the existing 300 deg$^2$ of LSST
simulated imaging produced as part of Dark Energy Science Collaboration (DESC)
Data Challenge 2 (DC2). Both synthetic surveys observe the same simulated DESC
DC2 universe. For the synthetic Roman survey, we simulate for the first time
fully chromatic images along with the detailed physics of the Sensor Chip
Assemblies derived from lab measurements using the flight detectors. The
simulated imaging and resulting pixel-level measurements of photometric
properties of objects span a wavelength range of $\sim$0.3 to 2.0 $\mu$m. We
also describe updates to the Roman simulation pipeline, changes in how
astrophysical objects are simulated relative to the original DC2 simulations,
and the resulting simulated Roman data products. We use these simulations to
explore the relative fraction of unrecognized blends in LSST images, finding
that 20-30% of objects identified in LSST images with $i$-band magnitudes
brighter than 25 can be identified as multiple objects in Roman images. These
simulations provide a unique testing ground for the development and validation
of joint pixel-level analysis techniques of ground- and space-based imaging
data sets in the second half of the 2020s -- in particular the case of joint
Roman--LSST analyses. | astro-ph_IM |
Kinematic Modelling of Disc Galaxies using Graphics Processing Units: With large-scale Integral Field Spectroscopy (IFS) surveys of thousands of
galaxies currently under-way or planned, the astronomical community is in need
of methods, techniques and tools that will allow the analysis of huge amounts
of data. We focus on the kinematic modelling of disc galaxies and investigate
the potential use of massively parallel architectures, such as the Graphics
Processing Unit (GPU), as an accelerator for the computationally expensive
model-fitting procedure. We review the algorithms involved in model-fitting and
evaluate their suitability for GPU implementation. We employ different
optimization techniques, including the Levenberg-Marquardt and Nested Sampling
algorithms, but also a naive brute-force approach based on Nested Grids. We
find that the GPU can accelerate the model-fitting procedure up to a factor of
~100 when compared to a single-threaded CPU, and up to a factor of ~10 when
compared to a multi-threaded dual CPU configuration. Our method's accuracy,
precision and robustness are assessed by successfully recovering the kinematic
properties of simulated data, and also by verifying the kinematic modelling
results of galaxies from the GHASP and DYNAMO surveys as found in the
literature. The resulting GBKFIT code is available for download from:
http://supercomputing.swin.edu.au/gbkfit. | astro-ph_IM |
A proposal for relative in-flight flux self-calibrations for
spectro-photometric surveys: We present a method for the in-flight relative flux self-calibration of a
spectro-photometer instrument, general enough to be applied to any upcoming
galaxy survey on satellite. The instrument response function, that accounts for
a smooth continuous variation due to telescope optics, on top of a
discontinuous effect due to the segmentation of the detector, is inferred with
a $\chi^2$ statistics. The method provides unbiased inference of the sources
count rates and of the reconstructed relative response function, in the limit
of high count rates. We simulate a simplified sequence of observations
following a spatial random pattern and realistic distributions of sources and
count rates, with the purpose of quantifying the relative importance of the
number of sources and exposures for correctly reconstructing the instrument
response. We present a validation of the method, with the definition of figures
of merit to quantify the expected performance, in plausible scenarios. | astro-ph_IM |
Target Detection Framework for Lobster Eye X-Ray Telescopes with Machine
Learning Algorithms: Lobster eye telescopes are ideal monitors to detect X-ray transients, because
they could observe celestial objects over a wide field of view in X-ray band.
However, images obtained by lobster eye telescopes are modified by their unique
point spread functions, making it hard to design a high efficiency target
detection algorithm. In this paper, we integrate several machine learning
algorithms to build a target detection framework for data obtained by lobster
eye telescopes. Our framework would firstly generate two 2D images with
different pixel scales according to positions of photons on the detector. Then
an algorithm based on morphological operations and two neural networks would be
used to detect candidates of celestial objects with different flux from these
2D images. At last, a random forest algorithm will be used to pick up final
detection results from candidates obtained by previous steps. Tested with
simulated data of the Wide-field X-ray Telescope onboard the Einstein Probe,
our detection framework could achieve over 94% purity and over 90% completeness
for targets with flux more than 3 mCrab (9.6 * 10-11 erg/cm2/s) and more than
94% purity and moderate completeness for targets with lower flux at acceptable
time cost. The framework proposed in this paper could be used as references for
data processing methods developed for other lobster eye X-ray telescopes. | astro-ph_IM |
Searching for high-energy neutrinos in coincidence with gravitational
waves with the ANTARES and VIRGO/LIGO detectors: Cataclysmic cosmic events can be plausible sources of both gravitational
waves (GW) and high-energy neutrinos (HEN). Both GW and HEN are alternative
cosmic messengers that may escape very dense media and travel unaffected over
cosmological distances, carrying information from the innermost regions of the
astrophysical engines. For the same reasons, such messengers could also reveal
new, hidden sources that were not observed by conventional photon astronomy.
Requiring the consistency between GW and HEN detection channels shall enable
new searches as one has significant additional information about the common
source. A neutrino telescope such as ANTARES can determine accurately the time
and direction of high energy neutrino events, while a network of gravitational
wave detectors such as LIGO and VIRGO can also provide timing/directional
information for gravitational wave bursts. By combining the information from
these totally independent detectors, one can search for cosmic events that may
arrive from common astrophysical sources. | astro-ph_IM |
A Laser Frequency Comb System for Absolute Calibration of the VTT
Echelle Spectrograph: A wavelength calibration system based on a laser frequency comb (LFC) was
developed in a co-operation between the Kiepenheuer-Institut f\"ur
Sonnenphysik, Freiburg, Germany and the Max-Planck-Institut f\"ur Quantenoptik,
Garching, Germany for permanent installation at the German Vacuum Tower
Telescope (VTT) on Tenerife, Canary Islands. The system was installed
successfully in October 2011. By simultaneously recording the spectra from the
Sun and the LFC, for each exposure a calibration curve can be derived from the
known frequencies of the comb modes that is suitable for absolute calibration
at the meters per second level. We briefly summarize some topics in solar
physics that benefit from absolute spectroscopy and point out the advantages of
LFC compared to traditional calibration techniques. We also sketch the basic
setup of the VTT calibration system and its integration with the existing
echelle spectrograph. | astro-ph_IM |
A Novel Technique to Observe Rapidly Pulsating Objects Using Spectral
Wave-Interaction Effects: Conventional techniques that measure rapid time variations are inefficient or
inadequate to discover and observe rapidly pulsating astronomical sources. It
is therefore conceivable that there exist some classes of objects pulsating
with extremely short periods that have not yet been discovered. This article
starts from the fact that rapid flux variations generate a spectral modulation
that can be detected in the beat spectrum of the output current fluctuations of
a quadratic detector. The telescope could observe at any frequency, although
shorter frequencies would have the advantage of lower photon noise. The
techniques would allow us to find and observe extremely fast time variations,
opening up a new time window in Astronomy. The current fluctuation technique,
like intensity interferometers, uses second-order correlation effects and fits
into the current renewal of interest in intensity interferometry. An
interesting aspect it shares with intensity interferometry is that it can use
inexpensive large telescope that have low-quality mirrors, like Cherenkov
telescopes. It has other advantages over conventional techniques that measure
time variations, foremost of which is its simplicity. Consequently, it could be
used for extended monitoring of astronomical sources, something that is
difficult to do with conventional telescopes. Arguably, the most interesting
scientific justification for the technique comes from Serendipity | astro-ph_IM |
A Cryogenic Integrated Noise Calibration and Coupler Module Using a MMIC
LNA: A new cryogenic noise calibration source for radio astronomy receivers is
presented. Dissipated power is only 4.2 mW, allowing it to be integrated with
the cold part of the receiver. Measured long-term stability, sensitivity to
bias voltages, and noise power output versus frequency are presented. The
measured noise output versus frequency is compared to a warm noise diode
injected into cryogenic K-band receiver and shows the integrated noise module
to have less frequency structure, which will result in more accurate
astronomical flux calibrations. It is currently in operation on the new
7-element K-band focal plane array receiver on the NRAO Robert C. Byrd Green
Bank Telescope (GBT). | astro-ph_IM |
Deep learning method for identifying mass composition of
ultra-high-energy cosmic rays: We introduce a novel method for identifying the mass composition of
ultra-high-energy cosmic rays using deep learning. The key idea of the method
is to use a chain of two neural networks. The first network predicts the type
of a primary particle for individual events, while the second infers the mass
composition of an ensemble of events. We apply this method to the Monte-Carlo
data for the Telescope Array Surface Detectors readings, on which it yields an
unprecedented low error of 7% for 4-component approximation. We also discuss
the problems of applying the developed method to the experimental data, and the
way they can be resolved. | astro-ph_IM |
Aerosol characterization using satellite remote sensing of light
pollution sources at night: A demanding challenge in atmospheric research is the night-time
characterization of aerosols using passive techniques, that is, by extracting
information from scattered light that has not been emitted by the observer.
Satellite observations of artificial night-time lights have been used to
retrieve some basic integral parameters, like the aerosol optical depth.
However, a thorough analysis of the scattering processes allows one to obtain
substantially more detailed information on aerosol properties. In this Letter
we demonstrate a practicable approach for determining the aerosol particle size
number distribution function in the air column, based on the measurement of the
angular radiance distribution of the scattered light emitted by night-time
lights of cities and towns, recorded from low Earth orbit. The method is
self-calibrating and does not require the knowledge of the absolute city
emissions. The input radiance data are readily available from several
spaceborne platforms, like the VIIRS-DNB radiometer onboard the Suomi-NPP
satellite. | astro-ph_IM |
Wavefront error tolerancing for direct imaging of exo-Earths with a
large segmented telescope in space: Direct imaging of exo-Earths and search for life is one of the most exciting
and challenging objectives for future space observatories. Segmented apertures
in space will be required to reach the needed large diameters beyond the
capabilities of current or planned launch vehicles. These apertures present
additional challenges for high-contrast coronagraphy, not only in terms of
static phasing but also in terms of their stability. The Pair-based Analytical
model for Segmented Telescope Imaging from Space (PASTIS) was developed to
model the effects of segment-level optical aberrations on the final image
contrast. In this paper, we extend the original PASTIS propagation model from a
purely analytical to a semi-analytical method, in which we substitute the use
of analytical images with numerically simulated images. The inversion of this
model yields a set of orthonormal modes that can be used to determine
segment-level wavefront tolerances. We present results in the case of
segment-level piston error applied to the baseline coronagraph design of LUVOIR
A, with minimum and maximum wavefront error constraint between 56 pm and 290 pm
per segment. The analysis is readily generalizable to other segment-level
aberrations modes, and can also be expanded to establish stability tolerances
for these missions. | astro-ph_IM |
A Visible-light Lyot Coronagraph for SCExAO/VAMPIRES: We describe the design and initial results from a visible-light Lyot
coronagraph for SCExAO/VAMPIRES. The coronagraph is comprised of four
hard-edged, partially transmissive focal plane masks with inner working angles
of 36 mas, 55 mas, 92 mas, and 129 mas, respectively. The Lyot stop is a
reflective, undersized design with a geometric throughput of 65.7%. Our
preliminary on-sky contrast is 1e-2 at 0.1" to 1e-4 at 0.75" for all mask
sizes. The coronagraph was deployed in early 2022 and is available for open
use. | astro-ph_IM |
SST-GATE: A dual mirror telescope for the Cherenkov Telescope Array: The Cherenkov Telescope Array (CTA) will be the world's first open
observatory for very high energy gamma-rays. Around a hundred telescopes of
different sizes will be used to detect the Cherenkov light that results from
gamma-ray induced air showers in the atmosphere. Amongst them, a large number
of Small Size Telescopes (SST), with a diameter of about 4 m, will assure an
unprecedented coverage of the high energy end of the electromagnetic spectrum
(above ~1TeV to beyond 100 TeV) and will open up a new window on the
non-thermal sky. Several concepts for the SST design are currently being
investigated with the aim of combining a large field of view (~9 degrees) with
a good resolution of the shower images, as well as minimizing costs. These
include a Davies-Cotton configuration with a Geiger-mode avalanche photodiode
(GAPD) based camera, as pioneered by FACT, and a novel and as yet untested
design based on the Schwarzschild-Couder configuration, which uses a secondary
mirror to reduce the plate-scale and to allow for a wide field of view with a
light-weight camera, e.g. using GAPDs or multi-anode photomultipliers. One
objective of the GATE (Gamma-ray Telescope Elements) programme is to build one
of the first Schwarzschild-Couder prototypes and to evaluate its performance.
The construction of the SST-GATE prototype on the campus of the Paris
Observatory in Meudon is under way. We report on the current status of the
project and provide details of the opto-mechanical design of the prototype, the
development of its control software, and simulations of its expected
performance. | astro-ph_IM |
Synthetic tracking using ZTF Long Dwell Datasets: The Zwicky Transit Factory (ZTF) is a powerful time domain survey facility
with a large field of view. We apply the synthetic tracking technique to
integrate a ZTF's long-dwell dataset, which consists of 133 nominal 30-second
exposure frames spanning about 1.5 hours, to search for slowly moving asteroids
down to approximately 23rd magnitude. We found more than one thousand objects
from searching 40 CCD-quadrant subfields, each of which covers a field size of
$\sim$0.73 deg$^2$. While most of the objects are main belt asteroids, there
are asteroids belonging to families of Trojan, Hilda, Hungaria, Phocaea, and
near-Earth-asteroids. Such an approach is effective and productive. Here we
report the data process and results. | astro-ph_IM |
PESummary: the code agnostic Parameter Estimation Summary page builder: PESummary is a Python software package for processing and visualising data
from any parameter estimation code. The easy to use Python executable scripts
and extensive online documentation has resulted in PESummary becoming a key
component in the international gravitational-wave analysis toolkit. PESummary
has been developed to be more than just a post-processing tool with all outputs
fully self-contained. PESummary has become central to making gravitational-wave
inference analysis open and easily reproducible. | astro-ph_IM |
Gaussian phase autocorrelation as an accurate compensator for FFT-based
atmospheric phase screen simulations: Accurately simulating the atmospheric turbulence behaviour is always
challenging. The well-known FFT based method falls short in correctly
predicting both the low and high frequency behaviours. Sub-harmonic
compensation aids in low-frequency correction but does not solve the problem
for all screen size to outer scale parameter ratios (G/$L_0$). FFT-based
simulation gives accurate result only for relatively large screen size to outer
scale parameter ratio (G/$L_0$). In this work, we have introduced a Gaussian
phase autocorrelation matrix to compensate for any sort of residual errors
after applying for a modified subharmonics compensation. With this, we have
solved problems such as under sampling at the high-frequency range, unequal
sampling/weights for subharmonics addition at low-frequency range and the patch
normalization factor. Our approach reduces the maximum error in phase
structure-function in the simulation with respect to theoretical prediction to
within 1.8\%, G/$L_0$ = 1/1000. | astro-ph_IM |
The Near Infrared Imager and Slitless Spectrograph for the James Webb
Space Telescope -- IV. Aperture Masking Interferometry: The James Webb Space Telescope's Near Infrared Imager and Slitless
Spectrograph (JWST-NIRISS) flies a 7-hole non-redundant mask (NRM), the first
such interferometer in space, operating at 3-5 \micron~wavelengths, and a
bright limit of $\simeq 4$ magnitudes in W2. We describe the NIRISS Aperture
Masking Interferometry (AMI) mode to help potential observers understand its
underlying principles, present some sample science cases, explain its
operational observing strategies, indicate how AMI proposals can be developed
with data simulations, and how AMI data can be analyzed. We also present key
results from commissioning AMI. Since the allied Kernel Phase Imaging (KPI)
technique benefits from AMI operational strategies, we also cover NIRISS KPI
methods and analysis techniques, including a new user-friendly KPI pipeline.
The NIRISS KPI bright limit is $\simeq 8$ W2 magnitudes. AMI (and KPI) achieve
an inner working angle of $\sim 70$ mas that is well inside the $\sim 400$ mas
NIRCam inner working angle for its circular occulter coronagraphs at comparable
wavelengths. | astro-ph_IM |
On Surface Brightness and Flux Calibration for Point and Compact
Extended Sources in the AKARI Far-IR All-Sky Survey (AFASS) Maps: The AKARI Infrared Astronomical Satellite produced the all-sky survey (AFASS)
maps in the far-IR at roughly arc-minute spatial resolution, enabling us to
investigate the whole sky in the far-IR for objects having surface brightnesses
greater than a few to a couple of dozen MJy/sr. While the AFASS maps are
absolutely calibrated against large-scale diffuse emission, it was uncertain
whether or not an additional flux correction for point sources was necessary.
Here, we verify that calibration for point-source photometry in the AFASS maps
is proper. With the aperture correction method based on the empirical
point-spread-function templates derived directly from the AFASS maps, fluxes in
the AKARI bright source catalogue (BSC) are reproduced. The AKARI BSC fluxes
are also satisfactorily recovered with the 1 sigma aperture, which is the
empirical equivalent of an infinite aperture. These results confirm that in the
AFASS maps far-IR photometry can be properly performed by using the aperture
correction method for point sources and by summing all pixel values within an
appropriately defined aperture of the intended target (i.e., the aperture
photometry method) for extended sources. | astro-ph_IM |
Waveguide-Type Multiplexer for Multiline Observation of Atmospheric
Molecules using Millimeter-Wave Spectroradiometer: In order to better understand the variation mechanism of ozone abundance in
the middle atmosphere, the simultaneous monitoring of ozone and other minor
molecular species, which are related to ozone depletion, is the most
fundamental and critical method. A waveguide-type multiplexer was developed for
the expansion of the observation frequency range of a millimeter-wave
spectroradiometer, for the simultaneous observation of multiple molecular
spectral lines. The proposed multiplexer contains a cascaded four-stage
sideband-separating filter circuit. The waveguide circuit was designed based on
electromagnetic analysis, and the pass frequency bands of Stages 1-4 were
243-251 GHz, 227-235 GHz, 197-205 GHz, and 181-189 GHz. The insertion and
return losses of the multiplexer were measured using vector network analyzers,
each observation band was well-defined, and the bandwidths were appropriately
specified. Moreover, the receiver noise temperature and the image rejection
ratio (IRR) using the superconducting mixer at 4 K were measured. As a result,
the increase in receiver noise due to the multiplexer compared with that of
only the mixer can be attributed to the transmission loss of the waveguide
circuit in the multiplexer. The IRRs were higher than 25 dB at the center of
each observation band. This indicates that a high and stable IRR performance
can be achieved by the waveguide-type multiplexer for the separation of
sideband signals. | astro-ph_IM |
Gaia Early Data Release 3. Building the Gaia DR3 source list --
Cross-match of Gaia observations: The Gaia Early Data Release 3 (Gaia EDR3) contains results derived from 78
billion individual field-of-view transits of 2.5 billion sources collected by
the European Space Agency's Gaia mission during its first 34 months of
continuous scanning of the sky. We describe the input data, which have the form
of onboard detections, and the modeling and processing that is involved in
cross-matching these detections to sources. For the cross-match, we formed
clusters of detections that were all linked to the same physical light source
on the sky. As a first step, onboard detections that were deemed spurious were
discarded. The remaining detections were then preliminarily associated with one
or more sources in the existing source list in an observation-to-source match.
All candidate matches that directly or indirectly were associated with the same
source form a match candidate group. The detections from the same group were
then subject to a cluster analysis. Each cluster was assigned a source
identifier that normally was the same as the identifiers from Gaia DR2. Because
the number of individual detections is very high, we also describe the
efficient organising of the processing. We present results and statistics for
the final cross-match with particular emphasis on the more complicated cases
that are relevant for the users of the Gaia catalogue. We describe the
improvements over the earlier Gaia data releases, in particular for stars of
high proper motion, for the brightest sources, for variable sources, and for
close source pairs. | astro-ph_IM |
Cleaning radio interferometric images using a spherical wavelet
decomposition: The deconvolution, or cleaning, of radio interferometric images often
involves computing model visibilities from a list of clean components, in order
that the contribution from the model can be subtracted from the observed
visibilities. This step is normally performed using a forward fast Fourier
transform (FFT), followed by a 'degridding' step that interpolates over the uv
plane to construct the model visibilities. An alternative approach is to
calculate the model visibilities directly by summing over all the members of
the clean component list, which is a more accurate method that can also be much
slower. However, if the clean components are used to construct a model image on
the surface of the celestial sphere then the model visibilities can be
generated directly from the wavelet coefficients, and the sparsity of the model
means that most of these coefficients are zero, and can be ignored. We have
constructed a prototype imager that uses a spherical-wavelet representation of
the model image to generate model visibilities during each major cycle, and
find empirically that the execution time scales with the wavelet resolution
level, J, as O(1.07 J), and with the number of distinct clean components, N_C,
as O(N_C). The prototype organises the wavelet coefficients into a tree
structure, and does not store or process the zero wavelet coefficients. | astro-ph_IM |
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