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Novel Back-coated Glass Mirrors for the MAGIC Telescopes: The mirrors installed on Imaging Atmospheric Cherenkov Telescopes like the
MAGIC telescopes in La Palma, Canary Islands, are constantly exposed to the
harsh environment. They have to withstand wind-induced corrosion from dust and
sand, changing temperatures, and rain. Because of the size of the telescope,
protecting the structure with a dome is not practical. The current mirrors used
in MAGIC are aluminum front-coated glass mirrors, covered by a thin quartz
layer. But even with this protective layer, significant decrease in
reflectivity can be seen on timescales of several years. The quartz layer is
very delicate and can be easily scratched or damaged, which also makes cleaning
the mirrors almost impossible. We have tested a novel design of glass mirrors
that can be easily cleaned and should show almost no degradation in
reflectivity due to environmental influences. The protective layer is a
ultra-thin glass sheet which is back-coated with aluminum, making it possible
to simply wipe the mirror with household cleaning tools. In this contribution
we will present results from laboratory tests of reflectivity and focusing
properties of prototype mirrors, as well as long-term tests on-site at the
MAGIC telescopes. We will also outline plans for exchanging a large fraction of
MAGIC mirrors with this novel design, guaranteeing a peak performance of MAGIC
for the coming years. | astro-ph_IM |
Segment-level thermal sensitivity analysis for exo-Earth imaging: We present a segment-level wavefront stability error budget for space
telescopes essential for exoplanet detection. We use a detailed finite element
model to relate the temperature gradient at the location of the primary mirror
to wavefront variations on each of the segment. We apply the PASTIS sensitivity
model forward approach to allocate static tolerances in physical units for each
segment, and transfer these tolerances to the temporal domain via a model of
the WFS&C architecture in combination with a Zernike phase sensor and science
camera. We finally estimate the close-loop variance and limiting contrast for
the segments' thermo-mechanical modes. | astro-ph_IM |
Analysis techniques and performance of the Domino Ring Sampler version 4
based readout for the MAGIC telescopes: Recently the readout of the MAGIC telescopes has been upgraded to a new
system based on the Domino Ring Sampler version 4 chip. We present the analysis
techniques and the signal extraction performance studies of this system. We
study the behaviour of the baseline, the noise, the cross-talk, the linearity
and the time resolution. We investigate also the optimal signal extraction. In
addition we show some of the analysis techniques specific to the readout based
on the Domino Ring Sampler version 2 chip, previously used in the MAGIC II
telescope. | astro-ph_IM |
A Template-Based Approach to the Photometric Classification of SN
1991bg-like Supernovae in the SDSS-II Supernova Survey: The use of Type Ia Supernovae (SNe Ia) to measure cosmological parameters has
grown significantly over the past two decades. However, there exists a
significant diversity in the SN Ia population that is not well understood.
Over-luminous SN 1991T-like and sub-luminous SN 1991bg-like objects are two
characteristic examples of peculiar SNe. The identification and classification
of such objects is an important step in studying what makes them unique from
the remaining SN population. With the upcoming Vera C. Rubin Observatory
promising on the order of a million new SNe over a ten-year survey,
spectroscopic classifications will be possible for only a small subset of
observed targets. As such, photometric classification has become an
increasingly important concern in preparing for the next generation of
astronomical surveys. Using observations from the Sloan Digital Sky Survey II
(SDSS-II) SN Survey, we apply here an empirically based classification
technique targeted at the identification of SN 1991bg-like SNe in photometric
data sets. By performing dedicated fits to photometric data in the rest-frame
redder and bluer bandpasses, we classify 16 previously unidentified 91bg-like
SNe. Using SDSS-II host-galaxy measurements, we find that these SNe are
preferentially found in host galaxies having an older average stellar age than
the hosts of normal SNe Ia. We also find that these SNe are found at a further
physical distance from the center of their host galaxies. We find no
statistically significant bias in host galaxy mass or specific star formation
rate for these targets. | astro-ph_IM |
Potential for measuring the longitudinal and lateral profile of muons in
TeV air showers with IACTs: Muons are copiously produced within hadronic extensive air showers (EAS)
occurring in the Earth's atmosphere, and are used by particle air shower
detectors as a means of identifying the primary cosmic ray which initiated the
EAS. Imaging Atmospheric Cherenkov Telescopes (IACTs), designed for the
detection of gamma-ray initiated EAS for the purposes of Very High Energy (VHE)
gamma-ray astronomy, are subject to a considerable background signal due to
hadronic EAS. Although hadronic EAS are typically rejected for gamma-ray
analysis purposes, single muons produced within such showers generate clearly
identifiable signals in IACTs and muon images are routinely retained and used
for calibration purposes. For IACT arrays operating with a stereoscopic
trigger, when a muon triggers one telescope, other telescopes in IACT arrays
usually detect the associated hadronic EAS. We demonstrate for the first time
the potential of IACT arrays for competitive measurements of the muon content
of air showers, their lateral distribution and longitudinal profile of
production slant heights in the TeV energy range. Such information can provide
useful input to hadronic interaction models. | astro-ph_IM |
Angular control noise in Advanced Virgo and implications for the
Einstein Telescope: With significantly improved sensitivity, the Einstein Telescope (ET), along
with other upcoming gravitational wave detectors, will mark the beginning of
precision gravitational wave astronomy. However, the pursuit of surpassing
current detector capabilities requires careful consideration of technical
constraints inherent in existing designs. The significant improvement of ET
lies in the low-frequency range, where it anticipates a one million-fold
increase in sensitivity compared to current detectors. Angular control noise is
a primary limitation for LIGO detectors in this frequency range, originating
from the need to maintain optical alignment. Given the expected improvements in
ET's low-frequency range, precise assessment of angular control noise becomes
crucial for achieving target sensitivity. To address this, we developed a model
of the angular control system of Advanced Virgo, closely matching experimental
data and providing a robust foundation for modeling future-generation
detectors. Our model, for the first time, enables replication of the measured
coupling level between angle and length. Additionally, our findings confirm
that Virgo, unlike LIGO, is not constrained by alignment control noise, even if
the detector were operating at full power. | astro-ph_IM |
A High-Resolution Atlas of Uranium-Neon in the H Band: We present a high-resolution (R ~ 50 000) atlas of a uranium-neon (U/Ne)
hollow-cathode spectrum in the H-band (1454 nm to 1638 nm) for the calibration
of near-infrared spectrographs. We obtained this U/Ne spectrum simultaneously
with a laser-frequency comb spectrum, which we used to provide a first-order
calibration to the U/Ne spectrum. We then calibrated the U/Ne spectrum using
the recently-published uranium line list of Redman et al. (2011), which is
derived from high-resolution Fourier transform spectrometer measurements. These
two independent calibrations allowed us to easily identify emission lines in
the hollow cathode lamp that do not correspond to known (classified) lines of
either uranium or neon, and to compare the achievable precision of each source.
Our frequency comb precision was limited by modal noise and detector effects,
while the U/Ne precision was limited primarily by the signal-to-noise ratio
(S/N) of the observed emission lines and our ability to model blended lines.
The standard deviation in the dispersion solution residuals from the
S/N-limited U/Ne hollow cathode lamp were 50% larger than the standard
deviation of the dispersion solution residuals from the modal-noise-limited
laser frequency comb. We advocate the use of U/Ne lamps for precision
calibration of near-infrared spectrographs, and this H-band atlas makes these
lamps significantly easier to use for wavelength calibration. | astro-ph_IM |
The Cherenkov Telescope Array: layout, design and performance: The Cherenkov Telescope Array (CTA) will be the next generation
very-high-energy gamma-ray observatory. CTA is expected to provide substantial
improvement in accuracy and sensitivity with respect to existing instruments
thanks to a tenfold increase in the number of telescopes and their
state-of-the-art design. Detailed Monte Carlo simulations are used to further
optimise the number of telescopes and the array layout, and to estimate the
observatory performance using updated models of the selected telescope designs.
These studies are presented in this contribution for the two CTA stations
located on the island of La Palma (Spain) and near Paranal (Chile) and for
different operation and observation conditions. | astro-ph_IM |
Photometric Data-driven Classification of Type Ia Supernovae in the Open
Supernova Catalog: We propose a novel approach for a machine-learning-based detection of the
type Ia supernovae using photometric information. Unlike other approaches, only
real observation data is used during training. Despite being trained on a
relatively small sample, the method shows good results on real data from the
Open Supernovae Catalog. We also investigate model transfer from the PLAsTiCC
simulations train dataset to real data application, and the reverse, and find
the performance significantly decreases in both cases, highlighting the
existing differences between simulated and real data. | astro-ph_IM |
Shrinkage MMSE estimators of covariances beyond the zero-mean and
stationary variance assumptions: We tackle covariance estimation in low-sample scenarios, employing a
structured covariance matrix with shrinkage methods. These involve convexly
combining a low-bias/high-variance empirical estimate with a biased
regularization estimator, striking a bias-variance trade-off. Literature
provides optimal settings of the regularization amount through risk
minimization between the true covariance and its shrunk counterpart. Such
estimators were derived for zero-mean statistics with i.i.d. diagonal
regularization matrices accounting for the average sample variance solely. We
extend these results to regularization matrices accounting for the sample
variances both for centered and non-centered samples. In the latter case, the
empirical estimate of the true mean is incorporated into our shrinkage
estimators. Introducing confidence weights into the statistics also enhance
estimator robustness against outliers. We compare our estimators to other
shrinkage methods both on numerical simulations and on real data to solve a
detection problem in astronomy. | astro-ph_IM |
Calculation of the Cherenkov light yield from low energetic secondary
particles accompanying high-energy muons in ice and water with Geant 4
simulations: In this work we investigate and parameterize the amount and angular
distribution of Cherenkov photons, which are generated by low-energy secondary
particles (typically $\lesssim 500 $\,MeV), which accompany a muon track in
water or ice. These secondary particles originate from small energy loss
processes. We investigate the contributions of the different energy loss
processes as a function of the muon energy and the maximum transferred energy.
For the calculation of the angular distribution we have developed a generic
transformation method, which allows us to derive the angular distribution of
Cherenkov photons for an arbitrary distribution of track directions and their
velocities. | astro-ph_IM |
A New Method for Determining Geometry of Planetary Images: This paper presents a novel semi-automatic image processing technique to
estimate accurately, and objectively, the disc parameters of a planetary body
on an astronomical image. The method relies on the detection of the limb and/or
the terminator of the planetary body with the VOronoi Image SEgmentation
(VOISE) algorithm (Guio and Achilleos, 2009). The resulting map of the
segmentation is then used to identify the visible boundary of the planetary
disc. The segments comprising this boundary are then used to perform a "best"
fit to an algebraic expression for the limb and/or terminator of the body. We
find that we are able to locate the centre of the planetary disc with an
accuracy of a few tens of one pixel. The method thus represents a useful
processing stage for auroral "imaging" based studies. | astro-ph_IM |
Analysis of defect formation in semiconductor cryogenic bolometric
detectors created by heavy dark matter: The cryogenic detectors in the form of bolometers are presently used for
different applications, in particular for very rare or hypothetical events
associated with new forms of matter, specifically related to the existence of
Dark Matter. In the detection of particles with a semiconductor as target and
detector, usually two signals are measured: ionization and heat. The
amplification of the thermal signal is obtained with the prescriptions from
Luke-Neganov effect. The energy deposited in the semiconductor lattice as
stable defects in the form of Frenkel pairs at cryogenic temperatures,
following the interaction of a dark matter particle, is evaluated and
consequences for measured quantities are discussed. This contribution is
included in the energy balance of the Luke effect. Applying the present model
to germanium and silicon, we found that for the same incident weakly
interacting massive particle the energy deposited in defects in germanium is
about twice the value for silicon. | astro-ph_IM |
Last performances improvement of the C-RED One camera using the 320x256
e-APD infrared Saphira detector: We present here the latest results obtained with the C-RED One camera
developed by First Light Imaging for fast ultra-low noise infrared
applications. This camera uses the Leonardo Saphira e-APD 320x256 infrared
sensor in an autonomous cryogenic environment with a low vibration pulse tube
and with embedded readout electronics system. Some recent improvements were
made to the camera. The first important one concerns the total noise of the
camera. Limited to 1.75 microns wavelength cut-off with proper cold filters,
looking at a blackbody at room temperature and f/4 beam aperture, we now
measure total noise down to 0.6 e at gain 50 in CDS mode 1720 FPS, dividing
previous noise figure by a factor 2. The total camera background of 30-400 e/s
is now achieved with a factor 3 of background reduction, the camera also
looking at a room temperature blackbody with an F/4 beam aperture. Image bias
oscillations, due to electronics grounding scheme, were carefully analyzed and
removed. Focal plane detector vibrations transmitted by the pulse tube cooling
machine were also analyzed, damped and measured down to 0.3 microns RMS,
reducing focal plane vibrations by a factor 3. In addition, a vacuum getter of
higher capacity is now used to offer camera operation without camera pumping
during months. The camera main characteristics are detailed: pulse tube cooling
at 80K with limited vibrations, permanent vacuum solution, ultra-low latency
Cameralink full data interface, safety management of the camera by firmware,
online firmware update, ambient liquid cooling and reduced weight of 20 kg. | astro-ph_IM |
(H)DPGMM: A Hierarchy of Dirichlet Process Gaussian Mixture Models for
the inference of the black hole mass function: We introduce (H)DPGMM, a hierarchical Bayesian non-parametric method based on
the Dirichlet Process Gaussian Mixture Model, designed to infer data-driven
population properties of astrophysical objects without being committal to any
specific physical model. We investigate the efficacy of our model on simulated
datasets and demonstrate its capability to reconstruct correctly a variety of
population models without the need of fine-tuning of the algorithm. We apply
our method to the problem of inferring the black hole mass function given a set
of gravitational wave observations from LIGO and Virgo, and find that the
(H)DPGMM infers a binary black hole mass function that is consistent with
previous estimates without the requirement of a theoretically motivated
parametric model. Although the number of systems observed is still too small
for a robust inference, (H)DPGMM confirms the presence of at least two distinct
modes in the observed merging black holes mass function, hence suggesting in a
model-independent fashion the presence of at least two classes of binary black
hole systems. | astro-ph_IM |
Reconstruction of radio signals from air-showers with autoencoder: The Tunka Radio Extension (Tunka-Rex) is a digital antenna array (63 antennas
distributed over 1km^2) co-located with the TAIGA observatory in Eastern
Siberia. Tunka-Rex measures radio emission of air-showers induced by ultra-high
energy cosmic rays in the frequency band of 30-80 MHz. Air-shower signal is a
short (tens of nanoseconds) broadband pulse. Using time positions and
amplitudes of these pulses, we reconstruct parameters of air showers and
primary cosmic rays. The amplitudes of low-energy event (E<10^17 eV) cannot be
used for successful reconstruction due to the domination of background. To
lower the energy threshold of the detection and increase the efficiency, we use
autoencoder neural network which removes noise from the measured data. This
work describes our approach to denoising raw data and further reconstruction of
air-shower parameters. We also present results of the low-energy events
reconstruction with autoencoder. | astro-ph_IM |
Analysing Astronomy Algorithms for GPUs and Beyond: Astronomy depends on ever increasing computing power. Processor clock-rates
have plateaued, and increased performance is now appearing in the form of
additional processor cores on a single chip. This poses significant challenges
to the astronomy software community. Graphics Processing Units (GPUs), now
capable of general-purpose computation, exemplify both the difficult
learning-curve and the significant speedups exhibited by massively-parallel
hardware architectures. We present a generalised approach to tackling this
paradigm shift, based on the analysis of algorithms. We describe a small
collection of foundation algorithms relevant to astronomy and explain how they
may be used to ease the transition to massively-parallel computing
architectures. We demonstrate the effectiveness of our approach by applying it
to four well-known astronomy problems: Hogbom CLEAN, inverse ray-shooting for
gravitational lensing, pulsar dedispersion and volume rendering. Algorithms
with well-defined memory access patterns and high arithmetic intensity stand to
receive the greatest performance boost from massively-parallel architectures,
while those that involve a significant amount of decision-making may struggle
to take advantage of the available processing power. | astro-ph_IM |
RFI excision using a higher order statistics analysis of the power
spectrum: A method of radio frequency interference (RFI) suppression in radio astronomy
spectral observations is described based on the analysis of the probability
distribution of an instantaneous spectrum. This method allows the separation of
the gaussian component due to the natural radio source and the non-gaussian RFI
signal. Examples are presented in the form of %computer simulations of this
method of RFI suppression and of WSRT observations with this method applied.
The application %of real time digital signal processing for RFI suppression is
found to be effective for radio astronomy telescopes %operating in a worsening
spectral environment. | astro-ph_IM |
Discovery and Characterization of a Faint Stellar Companion to the A3V
Star Zeta Virginis: Through the combination of high-order Adaptive Optics and coronagraphy, we
report the discovery of a faint stellar companion to the A3V star zeta
Virginis. This companion is ~7 magnitudes fainter than its host star in the
H-band, and infrared imaging spanning 4.75 years over five epochs indicates
this companion has common proper motion with its host star. Using evolutionary
models, we estimate its mass to be 0.168+/-.016 solar masses, giving a mass
ratio for this system q = 0.082. Assuming the two objects are coeval, this mass
suggests a M4V-M7V spectral type for the companion, which is confirmed through
integral field spectroscopic measurements. We see clear evidence for orbital
motion from this companion and are able to constrain the semi-major axis to be
greater than 24.9 AU, the period > 124$ yrs, and eccentricity > 0.16.
Multiplicity studies of higher mass stars are relatively rare, and binary
companions such as this one at the extreme low end of the mass ratio
distribution are useful additions to surveys incomplete at such a low mass
ratio. Moreover, the frequency of binary companions can help to discriminate
between binary formation scenarios that predict an abundance of low-mass
companions forming from the early fragmentation of a massive circumstellar
disk. A system such as this may provide insight into the anomalous X-ray
emission from A stars, hypothesized to be from unseen late-type stellar
companions. Indeed, we calculate that the presence of this M-dwarf companion
easily accounts for the X-ray emission from this star detected by ROSAT. | astro-ph_IM |
HiFLEx -- a highly flexible package to reduce cross-dispersed echelle
spectra: We describe a flexible data reduction package for high resolution
cross-dispersed echelle data. This open-source package is developed in Python
and includes optional GUIs for most of the steps. It does not require any
pre-knowledge about the form or position of the echelle-orders. It has been
tested on cross-dispersed echelle spectrographs between 13k and 115k resolution
(bifurcated fiber-fed spectrogaph ESO-HARPS and single fiber-fed spectrograph
TNT-MRES). HiFLEx can be used to determine radial velocities and is designed to
use the TERRA package but can also control the radial velocity packages such as
CERES and SERVAL to perform the radial velocity analysis. Tests on HARPS data
indicates radial velocities results within 3m/s of the literature pipelines
without any fine tuning of extraction parameters. | astro-ph_IM |
A Versatile Technique to Enable sub-milli-Kelvin Instrument Stability
for Precise Radial Velocity Measurements: Tests with the Habitable-zone
Planet Finder: Insufficient instrument thermo-mechanical stability is one of the many
roadblocks for achieving 10cm/s Doppler radial velocity (RV) precision, the
precision needed to detect Earth-twins orbiting Solar-type stars. Highly
temperature and pressure stabilized spectrographs allow us to better calibrate
out instrumental drifts, thereby helping in distinguishing instrumental noise
from astrophysical stellar signals. We present the design and performance of
the Environmental Control System (ECS) for the Habitable-zone Planet Finder
(HPF), a high-resolution (R=50,000) fiber-fed near infrared (NIR) spectrograph
for the 10m Hobby Eberly Telescope at McDonald Observatory. HPF will operate at
180K, driven by the choice of an H2RG NIR detector array with a 1.7micron
cutoff. This ECS has demonstrated 0.6mK RMS stability over 15 days at both 180K
and 300K, and maintained high quality vacuum (<$10^{-7}$Torr) over months,
during long-term stability tests conducted without a planned passive thermal
enclosure surrounding the vacuum chamber. This control scheme is versatile and
can be applied as a blueprint to stabilize future NIR and optical high
precision Doppler instruments over a wide temperature range from ~77K to
elevated room temperatures. A similar ECS is being implemented to stabilize
NEID, the NASA/NSF NN-EXPLORE spectrograph for the 3.5m WIYN telescope at Kitt
Peak, operating at 300K. A full SolidWorks 3D-CAD model and a comprehensive
parts list of the HPF ECS are included with this manuscript to facilitate the
adaptation of this versatile environmental control scheme in the broader
astronomical community. | astro-ph_IM |
Mitigating radio frequency interference in CHIME/FRB real-time intensity
data: Extragalactic fast radio bursts (FRBs) are a new class of astrophysical
transients with unknown origins that have become a main focus of radio
observatories worldwide. FRBs are highly energetic ($\sim 10^{36}$-$10^{42}$
ergs) flashes that last for about a millisecond. Thanks to its broad bandwidth
(400-800 MHz), large field of view ($\sim$200 sq. deg.), and massive data rate
(1500 TB of coherently beamformed data per day), the Canadian Hydrogen
Intensity Mapping Experiment / Fast Radio Burst (CHIME/FRB) project has
increased the total number of discovered FRBs by over a factor 10 in 3 years of
operation. CHIME/FRB observations are hampered by the constant exposure to
radio frequency interference (RFI) from artificial devices (e.g., cellular
phones, aircraft), resulting in $\sim$20% loss of bandwidth. In this work, we
describe our novel technique for mitigating RFI in CHIME/FRB real-time
intensity data. We mitigate RFI through a sequence of iterative operations,
which mask out statistical outliers from frequency-channelized intensity data
that have been effectively high-pass filtered. Keeping false positive and false
negative rates at very low levels, our approach is useful for any
high-performance surveys of radio transients in the future. | astro-ph_IM |
Prototype Open Event Reconstruction Pipeline for the Cherenkov Telescope
Array: The Cherenkov Telescope Array (CTA) is the next-generation gamma-ray
observatory currently under construction. It will improve over the current
generation of imaging atmospheric Cherenkov telescopes (IACTs) by a factor of
five to ten in sensitivity and it will be able to observe the whole sky from a
combination of two sites: a northern site in La Palma, Spain, and a southern
one in Paranal, Chile. CTA will also be the first open gamma-ray observatory.
Accordingly, the data analysis pipeline is developed as open-source software.
The event reconstruction pipeline accepts raw data of the telescopes and
processes it to produce suitable input for the higher-level science tools. Its
primary tasks include reconstructing the physical properties of each recorded
shower and providing the corresponding instrument response functions. ctapipe
is a framework providing algorithms and tools to facilitate raw data
calibration, image extraction, image parameterization and event reconstruction.
Its main focus is currently the analysis of simulated data but it has also been
successfully applied for the analysis of data obtained with the first CTA
prototype telescopes, such as the Large-Sized Telescope 1 (LST-1). pyirf is a
library to calculate IACT instrument response functions, needed to obtain
physics results like spectra and light curves, from the reconstructed event
lists. Building on these two, protopipe is a prototype for the event
reconstruction pipeline for CTA. Recent developments in these software packages
will be presented. | astro-ph_IM |
Unit panel nodes detection by CNN on FAST reflector: The 500-meter Aperture Spherical Radio Telescope(FAST) has an active
reflector. During the observation, the reflector will be deformed into a
paraboloid of 300-meters. To improve its surface accuracy, we propose a scheme
for photogrammetry to measure the positions of 2226 nodes on the reflector. And
the way to detect the nodes in the photos is the key problem in photogrammetry.
This paper applies Convolutional Neural Network(CNN) with candidate regions to
detect the nodes in the photos. The experiment results show a high recognition
rate of 91.5%, which is much higher than the recognition rate of traditional
edge detection. | astro-ph_IM |
An optimal method for scheduling observations of large sky error regions
for finding optical counterparts to transients: The discovery and subsequent study of optical counterparts to transient
sources is crucial for their complete astrophysical understanding. Various
gamma ray burst (GRB) detectors, and more notably the ground--based
gravitational wave detectors, typically have large uncertainties in the sky
positions of detected sources. Searching these large sky regions spanning
hundreds of square degrees is a formidable challenge for most ground--based
optical telescopes, which can usually image less than tens of square degrees of
the sky in a single night. We present algorithms for optimal scheduling of such
follow--up observations in order to maximize the probability of imaging the
optical counterpart, based on the all--sky probability distribution of the
source position. We incorporate realistic observing constraints like the
diurnal cycle, telescope pointing limitations, available observing time, and
the rising/setting of the target at the observatory location. We use
simulations to demonstrate that our proposed algorithms outperform the default
greedy observing schedule used by many observatories. Our algorithms are
applicable for follow--up of other transient sources with large positional
uncertainties, like Fermi--detected GRBs, and can easily be adapted for
scheduling radio or space--based X--ray followup. | astro-ph_IM |
Gamma-Ray Telescopes (in "400 Years of Astronomical Telescopes"): The last half-century has seen dramatic developments in gamma-ray telescopes,
from their initial conception and development through to their blossoming into
full maturity as a potent research tool in astronomy. Gamma-ray telescopes are
leading research in diverse areas such as gamma-ray bursts, blazars, Galactic
transients, and the Galactic distribution of aluminum-26. | astro-ph_IM |
A deep learning framework for jointly extracting spectra and
source-count distributions in astronomy: Astronomical observations typically provide three-dimensional maps, encoding
the distribution of the observed flux in (1) the two angles of the celestial
sphere and (2) energy/frequency. An important task regarding such maps is to
statistically characterize populations of point sources too dim to be
individually detected. As the properties of a single dim source will be poorly
constrained, instead one commonly studies the population as a whole, inferring
a source-count distribution (SCD) that describes the number density of sources
as a function of their brightness. Statistical and machine learning methods for
recovering SCDs exist; however, they typically entirely neglect spectral
information associated with the energy distribution of the flux. We present a
deep learning framework able to jointly reconstruct the spectra of different
emission components and the SCD of point-source populations. In a
proof-of-concept example, we show that our method accurately extracts even
complex-shaped spectra and SCDs from simulated maps. | astro-ph_IM |
Laue lenses: Focusing optics for hard X/soft Gamma-ray Astronomy: Hard X-/soft Gamma-ray astronomy is a key field for the study of important
astrophysical phenomena such as the electromagnetic counterparts of
gravitational waves, gamma-ray bursts, black holes physics and many more.
However, the spatial localization, imaging capabilities and sensitivity of the
measurements are strongly limited for the energy range $>$70 keV due to the
lack of focusing instruments operating in this energy band. A new generation of
instruments suitable to focus hard X-/ soft Gamma-rays is necessary to shed
light on the nature of astrophysical phenomena which are still unclear due to
the limitations of current direct-viewing telescopes. Laue lenses can be the
answer to those needs. A Laue lens is an optical device consisting of a large
number of properly oriented crystals which are capable, through Laue
diffraction, of concentrating the radiation into the common Laue lens focus. In
contrast with the grazing incidence telescopes commonly used for softer X-rays,
the transmission configuration of the Laue lenses allows us to obtain a
significant sensitive area even at energies of hundreds of keV. At the
University of Ferrara we are actively working on the modelization and
construction of a broad-band Laue lens. In this work we will present the main
concepts behind Laue lenses and the latest technological developments of the
TRILL (Technological Readiness Increase for Laue Lenses) project, devoted to
the advancement of the technological readiness of Laue lenses by developing the
first prototype of a lens sector made of cylindrical bent crystals of
Germanium. | astro-ph_IM |
On-sky measurements of atmospheric dispersion: I. Method validation: Observations with ground-based telescopes are affected by differential
atmospheric dispersion due to the wavelength-dependent index of refraction of
the atmosphere. The usage of an Atmospheric Dispersion Corrector (ADC) is
fundamental to compensate this effect. Atmospheric dispersion correction
residuals above the level of ~ 100 milli-arcseconds (mas) will affect
astronomical observations, in particular radial velocity and flux losses. The
design of an ADC is based on atmospheric models. To the best of our knowledge,
those models have never been tested on-sky. In this paper, we present a new
method to measure the atmospheric dispersion on-sky in the optical range. We
require an accuracy better than 50 mas that is equal to the difference between
atmospheric models. The method is based on the use of cross-dispersion
spectrographs to determine the position of the centroid of the spatial profile
at each wavelength of each spectral order. The method is validated using
cross-dispersed spectroscopic data acquired with the slit spectrograph UVES. We
measure an instrumental dispersion of 47 mas in the blue arm, 15 mas, and 23
mas in the two ranges of the red arm. We also measure a 4 % deviation in the
pixel scale from the value cited in UVES manual. The accuracy of the method is
~ 17 mas in the range of 315-665 nm. At this level, we can compare and
characterize different atmospheric dispersion models for better future ADC
designs. | astro-ph_IM |
Calibration of Radio Interferometers Using a Sparse DoA Estimation
Framework: The calibration of modern radio interferometers is a significant challenge,
specifically at low frequencies. In this perspective, we propose a novel
iterative calibration algorithm, which employs the popular sparse
representation framework, in the regime where the propagation conditions shift
dissimilarly the directions of the sources. More precisely, our algorithm is
designed to estimate the apparent directions of the calibration sources, their
powers, the directional and undirectional complex gains of the array elements
and their noise powers, with a reasonable computational complexity. Numerical
simulations reveal that the proposed scheme is statistically efficient at low
SNR and even with additional non-calibration sources at unknown directions. | astro-ph_IM |
Status of the TREND project: The Tianshan Radio Experiment for Neutrino Detection (TREND) is a sino-french
collaboration (CNRS/IN2P3 and Chinese Academy of Science) developing an
autonomous antenna array for the detection of high energy Extensive Air Showers
(EAS) on the site of the 21CMA radio observatory. The autonomous detection and
identification of EAS was achieved by TREND on a prototype array in 2009. This
result was confirmed soon after when EAS radio-candidates could be tagged as
cosmic ray events by an array of particle detectors running in parallel at the
same location. This result is an important milestone for TREND, and more
generally, for the maturation of the EAS radio-detection technique. The array
is presently composed of 50 antennas covering a total area of ~1.2 km^2,
running in steady conditions since March 2011. We are presently processing the
data to identify EAS radio-candidates. In a long term perspective, TREND is
intended to search for high energy tau neutrinos. Here we only report on the
results achieved so far by TREND. | astro-ph_IM |
Application of the TPB Wavelength Shifter to the DEAP-3600 Spherical
Acrylic Vessel Inner Surface: DEAP-3600 uses liquid argon contained in a spherical acrylic vessel as a
target medium to perform a sensitive spin-independent dark matter search. Argon
scintillates in the vacuum ultraviolet spectrum, which requires wavelength
shifting to convert the VUV photons to visible so they can be transmitted
through the acrylic light guides and detected by the surrounding
photomultiplier tubes. The wavelength shifter 1,1,4,4-tetraphenyl-1,3-butadiene
was evaporatively deposited to the inner surface of the acrylic vessel under
vacuum. Two evaporations were performed on the DEAP-3600 acrylic vessel with an
estimated coating thickness of 3.00 $\pm$ 0.02 $\mu$m which is successfully
wavelength shifting with liquid argon in the detector. Details on the
wavelength shifter coating requirements, deposition source, testing, and final
performance are presented. | astro-ph_IM |
Imaging Atmospheric Cherenkov Telescopes pointing determination using
the trajectories of the stars in the field of view: We present a new approach to the pointing determination of Imaging
Atmospheric Cherenkov Telescopes (IACTs). This method is universal and can be
applied to any IACT with minor modifications. It uses the trajectories of the
stars in the field of view of the IACT's main camera and requires neither
dedicated auxiliary hardware nor a specific data taking mode. The method
consists of two parts: firstly, we reconstruct individual star positions as a
function of time, taking into account the point spread function of the
telescope; secondly, we perform a simultaneous fit of all reconstructed star
trajectories using the orthogonal distance regression method. The method does
not assume any particular star trajectories, does not require a long
integration time, and can be applied to any IACT observation mode. The
performance of the method is assessed with commissioning data of the
Large-Sized Telescope prototype (LST-1), showing the method's stability and
remarkable pointing performance of the LST-1 telescope. | astro-ph_IM |
The Gaia Mission, Binary Stars and Exoplanets: On the 19th of December 2013, the Gaia spacecraft was successfully launched
by a Soyuz rocket from French Guiana and started its amazing journey to map and
characterise one billion celestial objects with its one billion pixel camera.
In this presentation, we briefly review the general aims of the mission and
describe what has happened since launch, including the Ecliptic Pole scanning
mode. We also focus especially on binary stars, starting with some basic
observational aspects, and then turning to the remarkable harvest that Gaia is
expected to yield for these objects. | astro-ph_IM |
The Radio Sky on Short Timescales with LOFAR: Pulsars and Fast
Transients: LOFAR, the "low-frequency array", will be one of the first in a new
generation of radio telescopes and Square Kilometer Array (SKA) pathfinders
that are highly flexible in capability because they are largely software
driven. LOFAR will not only open up a mostly unexplored spectral window, the
lowest frequency radio light observable from the Earth's surface, but it will
also be an unprecented tool with which to monitor the transient radio sky over
a large field of view and down to timescales of milliseconds or less. Here we
discuss LOFAR's current and upcoming capabilities for observing fast transients
and pulsars, and briefly present recent commissioning observations of known
pulsars. | astro-ph_IM |
Search for extreme energy cosmic ray candidates in the TUS orbital
experiment data: TUS (Track Ultraviolet Setup) is the first space experiment aimed to check
the possibility of registering extreme energy cosmic rays (EECRs) at E>50 EeV
by measuring the fluorescence signal of extensive air showers in the
atmosphere. The detector operates as a part of the scientific payload of the
Lomonosov satellite for more than a year. We describe an algorithm of searching
for EECR events in the TUS data and briefly discuss a number of candidates
selected by formal criteria. | astro-ph_IM |
Optical Astronomical Facilities at Nainital, India: Aryabhatta Research Institute of Observational Sciences (acronym ARIES)
operates a 1-m aperture optical telescope at Manora Peak, Nainital since 1972.
Considering the need and potential of establishing moderate size optical
telescope with spectroscopic capability at the geographical longitude of India,
the ARIES plans to establish a 3.6m new technology optical telescope at a new
site called Devasthal. This telescope will have instruments providing high
resolution spectral and seeing-limited imaging capabilities at visible and
near-infrared bands. A few other observing facilities with very specific goals
are also being established. A 1.3m aperture optical telescope to monitor
optically variable sources was installed at Devasthal in the year 2010 and a
0.5-m wide field (25 square degrees) Baker-Nunn Schmidt telescope to produce a
digital map of the Northern sky at optical bands was installed at Manora Peak
in 2011. A 4-m liquid mirror telescope for deep sky survey of transient sources
is planned at Devasthal. These optical facilities with specialized back-end
instruments are expected to become operational within the next few years and
can be used to optical studies of a wide variety of astronomical topics
including follow-up studies of sources identified in the radio region by GMRT
and UV/X-ray by ASTROSAT. | astro-ph_IM |
Using transfer learning to detect galaxy mergers: We investigate the use of deep convolutional neural networks (deep CNNs) for
automatic visual detection of galaxy mergers. Moreover, we investigate the use
of transfer learning in conjunction with CNNs, by retraining networks first
trained on pictures of everyday objects. We test the hypothesis that transfer
learning is useful for improving classification performance for small training
sets. This would make transfer learning useful for finding rare objects in
astronomical imaging datasets. We find that these deep learning methods perform
significantly better than current state-of-the-art merger detection methods
based on nonparametric systems like CAS and GM$_{20}$. Our method is end-to-end
and robust to image noise and distortions; it can be applied directly without
image preprocessing. We also find that transfer learning can act as a
regulariser in some cases, leading to better overall classification accuracy
($p = 0.02$). Transfer learning on our full training set leads to a lowered
error rate from 0.038 $\pm$ 1 down to 0.032 $\pm$ 1, a relative improvement of
15%. Finally, we perform a basic sanity-check by creating a merger sample with
our method, and comparing with an already existing, manually created merger
catalogue in terms of colour-mass distribution and stellar mass function. | astro-ph_IM |
fcmaker: automating the creation of ESO-compliant finding charts for
Observing Blocks on p2: fcmaker is a python module that creates astronomical finding charts for
Observing Blocks (OBs) on the p2 web server from the European Southern
Observatory (ESO). It provides users with the ability to automate the creation
of ESO-compliant finding charts for Service Mode and/or Visitor Mode OBs at the
Very Large Telescope (VLT). The design of the fcmaker finding charts, based on
an intimate knowledge of VLT observing procedures, is fine-tuned to best
support night time operations. As an automated tool, fcmaker also provides
observers with the means to independently check visually the observing sequence
coded inside an OB. This includes, for example, the signs of telescope and
position angle offsets. VLT instruments currently supported by fcmaker include
MUSE (WFM-AO, WFM-NOAO, NFM), HAWK-I (AO, NOAO), and X-shooter (full support).
The fcmaker code is published on a dedicated Github repository under the GNU
General Public License, and is also available via pypi. | astro-ph_IM |
The Infrared Imaging Spectrograph (IRIS) for TMT: Prototyping of
cryogenic compatible stage for the Imager: The IRIS Imager requires opt-mechanical stages which are operable under
vacuum and cryogenic environment. Also the stage for the IRIS Imager is
required to survive for 10 years without maintenance. To achieve these
requirements, we decided prototyping of a two axis stage with 80 mm clear
aperture. The prototype was designed as a double-deck stage, upper rotary stage
and lower linear stage. Most of components are selected to take advantage of
heritage from existing astronomical instruments. In contrast, mechanical
components with lubricants such as bearings, linear motion guides and ball
screws were modified to survive cryogenic environment. The performance proving
test was carried out to evaluate errors such as wobbling, rotary and linear
positioning error. We achieved 0.002 $\rm deg_{rms}$ wobbling, 0.08 $\rm
deg_{0-p}$ rotational positioning error and 0.07 $\rm mm_{0-p}$ translational
positioning error. Also durability test under anticipated load condition has
been conducted. In this article, we report the detail of mechanical design,
fabrication, performance and durability of the prototype. | astro-ph_IM |
Adaptive pupil masking for quasi-static speckle suppression: Quasi-static speckles are a current limitation to faint companion imaging of
bright stars. Here we show through simulation and theory that an adaptive pupil
mask can be used to reduce these speckles and increase the visibility of faint
companions. This is achieved by placing an adaptive mask in the conjugate pupil
plane of the telescope. The mask consists of a number of independently
controllable elements which can either allow the light in the subaperture to
pass or block it. This actively changes the shape of the telescope pupil and
hence the diffraction pattern in the focal plane. By randomly blocking
subapertures we force the quasi-static speckles to become dynamic. The long
exposure PSF is then smooth, absent of quasi-static speckles. However, as the
PSF will now contain a larger halo due to the blocking, the signal to noise
ratio (SNR) is reduced requiring longer exposure times to detect the companion.
For example, in the specific case of a faint companion at 5xlambda/D the
exposure time to achieve the same SNR will be increased by a factor of 1.35. In
addition, we show that the visibility of companions can be greatly enhanced in
comparison to long-exposures, when the dark speckle method is applied to short
exposure images taken with the adaptive pupil mask. We show that the contrast
ratio between PSF peak and the halo is then increased by a factor of
approximately 100 (5 magnitudes), and we detect companions 11 magnitudes
fainter than the star at 5xlambda/D and up to 18 magnitudes fainter at
22.5xlambda/D. | astro-ph_IM |
Comparative Analysis of the Observational Properties of Fast Radio
Bursts at the Frequencies of 111 and 1400 MHz: A comparative analysis of the observational characteristics of fast radio
bursts at the frequencies 111 and 1400 MHz is carried out. The distributions of
radio bursts by the dispersion measure are constructed. At both frequencies,
they are described by a lognormal distribution with the parameters $\mu =6.2$
$\sigma = 0.7$. The dependence $\tau_{sc}(DM)$ of the scattering value on the
dispersion measure at 111 MHz and 1400 MHz is also constructed. This dependence
is fundamentally different from the dependence for pulsars. A comparative
analysis of the relationship between the scattering of pulses and the
dispersion measure at 1400 MHz and 111 MHz showed that for both frequencies it
has the form $\tau_{sc}(DM)\sim DM^k$, where $k = 0.49 \pm 0.18$ and $k = 0.43
\pm 0.15$ for the frequencies 111 and 1400 MHz, respectively. The obtained
dependence is explained within the framework of the assumption of the
extragalactic occurrence of fast radio bursts and an almost uniform
distribution of matter in intergalactic space. From the dependence
$\tau_{sc}(DM)$ a total estimate of the contribution to the matter of the halo
of our and the host galaxy to $DM$ is obtained $DM_{halo} +
\frac{DM_{host}}{1+z}\approx 60\;{\rm pc/cm}^3$. Based on the LogN - LogS
dependence, the average spectral index of radio bursts is derived $\alpha = -
0.63 \pm 0.20$ provided that the statistical properties of these samples at 111
and 1400 MHz are the same. | astro-ph_IM |
Applications for Microwave Kinetic Induction Detectors in Advanced
Instrumentation: In recent years Microwave Kinetic Inductance Detectors (MKIDs) have emerged
as one of the most promising novel low temperature detector technologies. Their
unrivaled scalability makes them very attractive for many modern applications
and scientific instruments. In this paper we intend to give an overview of how
and where MKIDs are currently being used or are suggested to be used in the
future. MKID based projects are ongoing or proposed for observational
astronomy, particle physics, material science and THz imaging, and the goal of
this review is to provide an easily usable and thorough list of possible
starting points for more in-depth literature research on the many areas
profiting from kinetic inductance detectors. | astro-ph_IM |
X-ray performance of a customized large-format scientifc CMOS detector: In recent years, the performance of Scientifc Complementary Metal Oxide
Semiconductor (sCMOS) sensors has been improved signifcantly. Compared with CCD
sensors, sCMOS sensors have various advantages, making them potentially better
devices for optical and X-ray detection, especially in time-domain astronomy.
After a series of tests of sCMOS sensors, we proposed a new dedicated
high-speed, large-format X-ray detector in 2016 cooperating with Gpixel Inc.
This new sCMOS sensor has a physical size of 6 cm by 6 cm, with an array of
4096 by 4096 pixels and a pixel size of 15 um. The frame rate is 20.1 fps under
current condition and can be boosted to a maximum value around 100 fps. The
epitaxial thickness is increased to 10 um compared to the previous sCMOS
product. We show the results of its frst taped-out product in this work. The
dark current of this sCMOS is lower than 10 e/pixel/s at 20C, and lower than
0.02 e/pixel/s at -30C. The Fixed Pattern Noise (FPN) and the readout noise are
lower than 5 e in high-gain situation and show a small increase at low
temperature. The energy resolution reaches 180.1 eV (3.1%) at 5.90 keV for
single-pixel events and 212.3 eV (3.6%) for all split events. The continuous
X-ray spectrum measurement shows that this sensor is able to response to X-ray
photons from 500 eV to 37 keV. The excellent performance, as demonstrated from
these test results, makes sCMOS sensor an ideal detector for X-ray imaging and
spectroscopic application. | astro-ph_IM |
Design and operation of the ATLAS Transient Science Server: The Asteroid Terrestrial impact Last Alert System (ATLAS) system consists of
two 0.5m Schmidt telescopes with cameras covering 29 square degrees at plate
scale of 1.86 arcsec per pixel. Working in tandem, the telescopes routinely
survey the whole sky visible from Hawaii (above $\delta > -50^{\circ}$) every
two nights, exposing four times per night, typically reaching $o < 19$
magnitude per exposure when the moon is illuminated and $c < 19.5$ per exposure
in dark skies. Construction is underway of two further units to be sited in
Chile and South Africa which will result in an all-sky daily cadence from 2021.
Initially designed for detecting potentially hazardous near earth objects, the
ATLAS data enable a range of astrophysical time domain science. To extract
transients from the data stream requires a computing system to process the
data, assimilate detections in time and space and associate them with known
astrophysical sources. Here we describe the hardware and software
infrastructure to produce a stream of clean, real, astrophysical transients in
real time. This involves machine learning and boosted decision tree algorithms
to identify extragalactic and Galactic transients. Typically we detect 10-15
supernova candidates per night which we immediately announce publicly. The
ATLAS discoveries not only enable rapid follow-up of interesting sources but
will provide complete statistical samples within the local volume of 100 Mpc. A
simple comparison of the detected supernova rate within 100 Mpc, with no
corrections for completeness, is already significantly higher (factor 1.5 to 2)
than the current accepted rates. | astro-ph_IM |
Planck LFI flight model feed horns: this paper is part of the Prelaunch status LFI papers published on JINST:
http://www.iop.org/EJ/journal/-page=extra.proc5/jinst The Low Frequency
Instrument is optically interfaced with the ESA Planck telescope through 11
corrugated feed horns each connected to the Radiometer Chain Assembly (RCA).
This paper describes the design, the manufacturing and the testing of the
flight model feed horns. They have been designed to optimize the LFI optical
interfaces taking into account the tight mechanical requirements imposed by the
Planck focal plane layout. All the eleven units have been successfully tested
and integrated with the Ortho Mode transducers. | astro-ph_IM |
Investigation of Correction Method of the Spacecraft Low Altitude
Ranging: gamma ray altitude control system is an important equipment for deep space
exploration and sample return mission, its main purpose is a low altitude
measurement of the spacecraft based on Compton Effect at the moment when it
lands on extraterrestrial celestial or sampling returns to the Earth land, and
an ignition altitude correction of the spacecraft retrograde landing rocket at
different landing speeds. This paper presents an ignition altitude correction
method of the spacecraft at different landing speeds, based on the number of
particles gamma ray reflected field gradient graded. Through the establishment
of a theoretical model, its algorithm feasibility is proved by a mathematical
derivation and verified by an experiment, and also the adaptability of the
algorithm under different parameters is described. The method provides a
certain value for landing control of the deep space exploration spacecraft
landing the planet surface. | astro-ph_IM |
Amplitude Correction Factors of KVN Observations: We report results of investigation of amplitude calibration for very long
baseline interferometry (VLBI) observations with Korean VLBI Network (KVN).
Amplitude correction factors are estimated based on comparison of KVN
observations at 22~GHz correlated by Daejeon hardware correlator and DiFX
software correlator in Korea Astronomy and Space Science Institute (KASI) with
Very Long Baseline Array (VLBA) observations at 22~GHz by DiFX software
correlator in National Radio Astronomy Observatory (NRAO). We used the
observations for compact radio sources, 3C 454.3, NRAO 512, OJ 287, BL Lac, 3C
279, 1633+382, and 1510-089, which are almost unresolved for baselines in a
range of 350-477 km. Visibility data of the sources obtained with similar
baselines at KVN and VLBA are selected, fringe-fitted, calibrated, and compared
for their amplitudes. We found that visibility amplitudes of KVN observations
should be corrected by factors of 1.10 and 1.35 when correlated by DiFX and
Daejeon correlators, respectively. These correction factors are attributed to
the combination of two steps of 2-bit quantization in KVN observing systems and
characteristics of Daejeon correlator. | astro-ph_IM |
High-speed X-ray imaging spectroscopy system with Zynq SoC for solar
observations: We have developed a system combining a back-illuminated
Complementary-Metal-Oxide-Semiconductor (CMOS) imaging sensor and Xilinx Zynq
System-on-Chip (SoC) device for a soft X-ray (0.5-10 keV) imaging spectroscopy
observation of the Sun to investigate the dynamics of the solar corona. Because
typical timescales of energy release phenomena in the corona span a few minutes
at most, we aim to obtain the corresponding energy spectra and derive the
physical parameters, i.e., temperature and emission measure, every few tens of
seconds or less for future solar X-ray observations. An X-ray photon-counting
technique, with a frame rate of a few hundred frames per second or more, can
achieve such results. We used the Zynq SoC device to achieve the requirements.
Zynq contains an ARM processor core, which is also known as the Processing
System (PS) part, and a Programmable Logic (PL) part in a single chip. We use
the PL and PS to control the sensor and seamless recording of data to a storage
system, respectively. We aim to use the system for the third flight of the
Focusing Optics Solar X-ray Imager (FOXSI-3) sounding rocket experiment for the
first photon-counting X-ray imaging and spectroscopy of the Sun. | astro-ph_IM |
The PRL 2.5m Telescope and its First Light Instruments: FOC & PARAS-2: We present here the information on the design and performance of the recently
commissioned 2.5-meter telescope at the PRL Mount Abu Observatory, located at
Gurushikhar, Mount Abu, India. The telescope has been successfully installed at
the site, and the Site Acceptance Test (SAT) was completed in October 2022. It
is a highly advanced telescope in India, featuring the
Ritchey-Chr$\acute{e}$tien optical configuration with primary mirror active
optics, tip-tilt on side-port, and wave front correction sensors. Along with
the telescope, its two first light instruments {namely Faint Object Camera
(FOC) and PARAS-2} were also integrated and attached with it in the June 2022.
{FOC is a} camera that uses a 4096 X 4112 pixels detector SDSS type filters
with enhanced transmission and known as u', g', r', i', z'. It has a limiting
magnitude of 21 mag in 10 minutes exposure in the r'-band. The other first
light instrument PARAS-2 is a state-of-the-art high-resolution fiber-fed
spectrograph operates in 380-690 nm wave-band, aimed to unveil the super-Earth
like worlds. The spectrograph works at a resolution of $\sim$107,000, making it
the highest-resolution spectrograph in Asia to date, which is under
{ultra}-stable temperature and pressure environment, at 22.5 $\pm$ 0.001
$^{\circ}$C and 0.005 $\pm$ 0.0005 mbar, respectively. Initial calibration
tests of the spectrograph using a Uranium Argon Hollow Cathode Lamp (UAr HCL)
have yielded intrinsic instrumental RV stability down to 30 cm s$^{-1}$. | astro-ph_IM |
Investigation of dust grains by optical tweezers for space applications: Cosmic dust plays a dominant role in the universe, especially in the
formation of stars and planetary systems. Furthermore, the surface of cosmic
dust grains is the bench-work where molecular hydrogen and simple organic
compounds are formed. We manipulate individual dust particles in water solution
by contactless and non-invasive techniques such as standard and Raman tweezers,
to characterize their response to mechanical effects of light (optical forces
and torques) and to determine their mineral compositions. Moreover, we show
accurate optical force calculations in the T-matrix formalism highlighting the
key role of composition and complex morphology in optical trapping of cosmic
dust particles.This opens perspectives for future applications of optical
tweezers in curation facilities for sample return missions or in
extraterrestrial environments. | astro-ph_IM |
The Chinese space millimeter-wavelength VLBI array - a step toward
imaging the most compact astronomical objects: The Shanghai Astronomical Observatory (SHAO) of the Chinese Academy of
Sciences (CAS) is studying a space VLBI (Very Long Baseline Interferometer)
program. The ultimate objective of the program is to image the immediate
vicinity of the supermassive black holes (SMBHs) in the hearts of galaxies with
a space-based VLBI array working at sub-millimeter wavelengths and to gain
ultrahigh angular resolution. To achieve this ambitious goal, the mission plan
is divided into three stages. The first phase of the program is called Space
Millimeter-wavelength VLBI Array (SMVA) consisting of two satellites, each
carrying a 10-m diameter radio telescope into elliptical orbits with an apogee
height of 60000 km and a perigee height of 1200 km. The VLBI telescopes in
space will work at three frequency bands, 43, 22 and 8 GHz. The 43- and 22-GHz
bands will be equipped with cryogenic receivers. The space telescopes,
observing together with ground-based radio telescopes, enable the highest
angular resolution of 20 micro-arcsecond ($\mu$as) at 43 GHz. The SMVA is
expected to conduct a broad range of high-resolution observational research,
e.g. imaging the shadow (dark region) of the supermassive black hole in the
heart of the galaxy M87 for the first time, studying the kinematics of water
megamasers surrounding the SMBHs, and exploring the power source of active
galactic nuclei. Pre-research funding has been granted by the CAS in October
2012, to support scientific and technical feasibility studies. These studies
also include the manufacturing of a prototype of the deployable 10-m
space-based telescope and a 22-GHz receiver. Here we report on the latest
progress of the SMVA project. | astro-ph_IM |
A Floating Octave Bandwidth Cone-Disc Antenna for Detection of Cosmic
Dawn: The critical component of radio astronomy radiometers built to detect
redshifted 21-cm signals from Cosmic Dawn is the antenna element. We describe
the design and performance of an octave bandwidth cone disc antenna built to
detect this signal in the band 40 to 90 MHz. The Cosmic Dawn signal is
predicted to be a wideband spectral feature orders of magnitude weaker than sky
and ground radio brightness. Thus, the engineering challenge is to design an
antenna at low frequencies that is able to provide with high fidelity the faint
cosmological signal, along with foreground sky, to the receiver. The antenna
characteristics must not compromise detection by imprinting any confusing
spectral features on the celestial radiation, ground emission or receiver
noise. An innovation in the present design is making the antenna electrically
smaller than half wavelength and operating it on the surface of a sufficiently
large water body. The homogeneous and high permittivity medium beneath the
small cone-disc antenna results in an achromatic beam pattern, high radiation
efficiency and minimum unwanted confusing spectral features. The antenna design
was optimized in WIPL-D and FEKO. A prototype was constructed and deployed on a
lake to validate its performance with field measurements.
Index Terms: Antenna measurements, radio astronomy, reflector antennas. | astro-ph_IM |
Reconstruction of signals with unknown spectra in information field
theory with parameter uncertainty: The optimal reconstruction of cosmic metric perturbations and other signals
requires knowledge of their power spectra and other parameters. If these are
not known a priori, they have to be measured simultaneously from the same data
used for the signal reconstruction. We formulate the general problem of signal
inference in the presence of unknown parameters within the framework of
information field theory. We develop a generic parameter uncertainty
renormalized estimation (PURE) technique and address the problem of
reconstructing Gaussian signals with unknown power-spectrum with five different
approaches: (i) separate maximum-a-posteriori power spectrum measurement and
subsequent reconstruction, (ii) maximum-a-posteriori power reconstruction with
marginalized power-spectrum, (iii) maximizing the joint posterior of signal and
spectrum, (iv) guessing the spectrum from the variance in the Wiener filter
map, and (v) renormalization flow analysis of the field theoretical problem
providing the PURE filter. In all cases, the reconstruction can be described or
approximated as Wiener filter operations with assumed signal spectra derived
from the data according to the same recipe, but with differing coefficients.
All of these filters, except the renormalized one, exhibit a perception
threshold in case of a Jeffreys prior for the unknown spectrum. Data modes,
with variance below this threshold do not affect the signal reconstruction at
all. Filter (iv) seems to be similar to the so called Karhune-Loeve and
Feldman-Kaiser-Peacock estimators for galaxy power spectra used in cosmology,
which therefore should also exhibit a marginal perception threshold if
correctly implemented. We present statistical performance tests and show that
the PURE filter is superior to the others. | astro-ph_IM |
Real-time Adaptive Optics with pyramid wavefront sensors: Accurate
wavefront reconstruction using iterative methods: In this paper, we address the inverse problem of fast, stable, and
high-quality wavefront reconstruction from pyramid wavefront sensor data for
Adaptive Optics systems on Extremely Large Telescopes. For solving the
indicated problem we apply well-known iterative mathematical algorithms, namely
conjugate gradient, steepest descent, Landweber, Landweber-Kaczmarz and
steepest descent-Kaczmarz iteration based on theoretical studies of the pyramid
wavefront sensor. We compare the performance (in terms of correction quality
and speed) of these algorithms in end-to-end numerical simulations of a closed
adaptive loop. The comparison is performed in the context of a high-order SCAO
system for METIS, one of the first-light instruments currently under design for
the Extremely Large Telescope. We show that, though being iterative, the
analyzed algorithms, when applied in the studied context, can be implemented in
a very efficient manner, which reduces the related computational effort
significantly. We demonstrate that the suggested analytically developed
approaches involving iterative algorithms provide comparable quality to
standard matrix-vector-multiplication methods while being computationally
cheaper. | astro-ph_IM |
Two-element interferometer for millimeter-wave solar flare observations: In this paper, we present the design and implementation of a two-element
interferometer working in the millimeter wave band (39.5 GHz - 40 GHz) for
observing solar radio emissions through nulling interference. The system is
composed of two 50 cm aperture Cassegrain antennas mounted on a common
equatorial mount, with a separation of 230 wavelengths. The cross-correlation
of the received signals effectively cancels the quiet solar component of the
large flux density (~3000 sfu) that reduces the detection limit due to
atmospheric fluctuations. The system performance is obtained as follows: the
noise factor of the AFE in the observation band is less than 2.1 dB, system
sensitivity is approximately 12.4 K (~34 sfu) with an integration time constant
of 0.1 ms (default), the frequency resolution is 153 kHz, and the dynamic range
is larger than 30 dB. Through actual testing, the nulling interferometer
observes a quiet sun with a low level of output fluctuations (of up to 50 sfu)
and has a significantly lower radiation flux variability (of up to 190 sfu)
than an equivalent single-antenna system, even under thick cloud cover. As a
result, this new design can effectively improve observation sensitivity by
reducing the impact of atmospheric and system fluctuations during observation. | astro-ph_IM |
Quasar Microlensing Models with Constraints on the Quasar Light Curves: Quasar microlensing analyses implicitly generate a model of the variability
of the source quasar. The implied source variability may be unrealistic yet its
likelihood is generally not evaluated. We used the damped random walk (DRW)
model for quasar variability to evaluate the likelihood of the source
variability and applied the revised algorithm to a microlensing analysis of the
lensed quasar RX J1131-1231. We compared the estimates of the source quasar
disk and average lens galaxy stellar mass with and without applying the DRW
likelihoods for the source variability model and found no significant effect on
the estimated physical parameters. The most likely explanation is that
unreliastic source light curve models are generally associated with poor
microlensing fits that already make a negligible contribution to the
probability distributions of the derived parameters. | astro-ph_IM |
SPHERE on-sky performance compared with budget predictions: The SPHERE (spectro-photometric exoplanet research) extreme-AO planet hunter
saw first light at the VLT observatory on Mount Paranal in May 2014 after ten
years of development. Great efforts were put into modelling its performance,
particularly in terms of achievable contrast, and to budgeting instrumental
features such as wave front errors and optical transmission to each of the
instrument's three focal planes, the near infrared dual imaging camera IRDIS,
the near infrared integral field spectrograph IFS and the visible polarimetric
camera ZIMPOL. In this paper we aim at comparing predicted performance with
measured performance. In addition to comparing on-sky contrast curves and
calibrated transmission measurements, we also compare the PSD-based wave front
error budget with in-situ wave front maps obtained thanks to a Zernike phase
mask, ZELDA, implemented in the infrared coronagraph wheel. One of the most
critical elements of the SPHERE system is its high-order deformable mirror, a
prototype 40x40 actuator piezo stack design developed in parallel with the
instrument itself. The development was a success, as witnessed by the
instrument performance, in spite of some bad surprises discovered on the way.
The devastating effects of operating without taking properly into account the
loss of several actuators and the thermally and temporally induced variations
in the DM shape will be analysed, and the actions taken to mitigate these
defects through the introduction of specially designed Lyot stops and
activation of one of the mirrors in the optical train will be described. | astro-ph_IM |
Detailed Studies of Atmospheric Calibration in Imaging Cherenkov
Astronomy: The current generation of Imaging Atmospheric Cherenkov telescopes are
allowing the sky to be probed with greater sensitivity than ever before in the
energy range around and above 100 GeV. To minimise the systematic errors on
derived fluxes a full calibration of the atmospheric properties is important
given the calorimetric nature of the technique. In this paper we discuss an
approach to address this problem by using a ceilometer co-pointed with the
H.E.S.S. telescopes and present the results of the application of this method
to a set of observational data taken on the active galactic nucleus (AGN) PKS
2155-304 in 2004. | astro-ph_IM |
Visualising three-dimensional volumetric data with an arbitrary
coordinate system: Astronomical data does not always use Cartesian coordinates. Both all-sky
observational data and simulations of rotationally symmetric systems, such as
accretion and protoplanetary discs, may use spherical polar or other coordinate
systems. Standard displays rely on Cartesian coordinates, but converting
non-Cartesian data into Cartesian format causes distortion of the data and loss
of detail. I here demonstrate a method using standard techniques from computer
graphics that avoids these problems with 3D data in arbitrary coordinate
systems. The method adds minimum computational cost to the display process and
is suitable for both realtime, interactive content and producing fixed rendered
images and videos. Proof-of-concept code is provided which works for data in
spherical polar coordinates. | astro-ph_IM |
Fast gravitational wave parameter estimation without compromises: We present a lightweight, flexible, and high-performance framework for
inferring the properties of gravitational-wave events. By combining likelihood
heterodyning, automatically-differentiable and accelerator-compatible
waveforms, and gradient-based Markov chain Monte Carlo (MCMC) sampling enhanced
by normalizing flows, we achieve full Bayesian parameter estimation for real
events like GW150914 and GW170817 within a minute of sampling time. Our
framework does not require pretraining or explicit reparameterizations and can
be generalized to handle higher dimensional problems. We present the details of
our implementation and discuss trade-offs and future developments in the
context of other proposed strategies for real-time parameter estimation. Our
code for running the analysis is publicly available on GitHub
https://github.com/kazewong/jim. | astro-ph_IM |
Application of Deep Learning methods to analysis of Imaging Atmospheric
Cherenkov Telescopes data: Ground based gamma-ray observations with Imaging Atmospheric Cherenkov
Telescopes (IACTs) play a significant role in the discovery of very high energy
(E > 100 GeV) gamma-ray emitters. The analysis of IACT data demands a highly
efficient background rejection technique, as well as methods to accurately
determine the energy of the recorded gamma-ray and the position of its source
in the sky. We present results for background rejection and signal direction
reconstruction from first studies of a novel data analysis scheme for IACT
measurements. The new analysis is based on a set of Convolutional Neural
Networks (CNNs) applied to images from the four H.E.S.S. phase-I telescopes. As
the H.E.S.S. cameras pixels are arranged in a hexagonal array, we demonstrate
two ways to use such image data to train CNNs: by resampling the images to a
square grid and by applying modified convolution kernels that conserve the
hexagonal grid properties.
The networks were trained on sets of Monte-Carlo simulated events and tested
on both simulations and measured data from the H.E.S.S. array. A comparison
between the CNN analysis to current state-of-the-art algorithms reveals a clear
improvement in background rejection performance. When applied to H.E.S.S.
observation data, the CNN direction reconstruction performs at a similar level
as traditional methods. These results serve as a proof-of-concept for the
application of CNNs to the analysis of events recorded by IACTs. | astro-ph_IM |
METAPHOR: Probability density estimation for machine learning based
photometric redshifts: We present METAPHOR (Machine-learning Estimation Tool for Accurate
PHOtometric Redshifts), a method able to provide a reliable PDF for photometric
galaxy redshifts estimated through empirical techniques. METAPHOR is a modular
workflow, mainly based on the MLPQNA neural network as internal engine to
derive photometric galaxy redshifts, but giving the possibility to easily
replace MLPQNA with any other method to predict photo-z's and their PDF. We
present here the results about a validation test of the workflow on the
galaxies from SDSS-DR9, showing also the universality of the method by
replacing MLPQNA with KNN and Random Forest models. The validation test include
also a comparison with the PDF's derived from a traditional SED template
fitting method (Le Phare). | astro-ph_IM |
Characterization and Optimization of Skipper CCDs for the SOAR Integral
Field Spectrograph: We present results from the characterization and optimization of six Skipper
CCDs for use in a prototype focal plane for the SOAR Integral Field
Spectrograph (SIFS). We tested eight Skipper CCDs and selected six for SIFS
based on performance results. The Skipper CCDs are 6k $\times$ 1k, 15 $\mu$m
pixels, thick, fully-depleted, $p$-channel devices that have been thinned to
$\sim 250 \mu$m, backside processed, and treated with an antireflective
coating. We optimize readout time to achieve $<4.3$ e$^-$ rms/pixel in a single
non-destructive readout and $0.5$ e$^-$ rms/pixel in $5 \%$ of the detector. We
demonstrate single-photon counting with $N_{\rm samp}$ = 400 ($\sigma_{\rm
0e^-} \sim$ 0.18 e$^-$ rms/pixel) for all 24 amplifiers (four amplifiers per
detector). We also perform conventional CCD characterization measurements such
as cosmetic defects ($ <0.45 \%$ ``bad" pixels), dark current ($\sim 2 \times
10^{-4}$ e$^-$/pixel/sec.), charge transfer inefficiency ($3.44 \times 10^{-7}$
on average), and charge diffusion (PSF $< 7.5 \mu$m). We report on
characterization and optimization measurements that are only enabled by
photon-counting. Such results include voltage optimization to achieve full-well
capacities $\sim 40,000-63,000$ e$^-$ while maintaining photon-counting
capabilities, clock induced charge optimization, non-linearity measurements at
low signals (few tens of electrons). Furthermore, we perform measurements of
the brighter-fatter effect and absolute quantum efficiency ($\gtrsim\, 80 \%$
between 450 nm and 980 nm; $\gtrsim\,90 \%$ between 600 nm and 900 nm) using
Skipper CCDs. | 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 |
Effect of filters on the time-delay interferometry residual laser noise
for LISA: The Laser Interferometer Space Antenna (LISA) is a European Space Agency
mission that aims to measure gravitational waves in the millihertz range. Laser
frequency noise enters the interferometric measurements and dominates the
expected gravitational signals by many orders of magnitude. Time-delay
interferometry (TDI) is a technique that reduces this laser noise by
synthesizing virtual equal-arm interferometric measurements. Laboratory
experiments and numerical simulations have confirmed that this reduction is
sufficient to meet the scientific goals of the mission in proof-of-concept
setups. In this paper, we show that the on-board antialiasing filters play an
important role in TDI's performance when the flexing of the constellation is
accounted for. This coupling was neglected in previous studies. To reach an
optimal reduction level, filters with vanishing group delays must be used on
board or synthesized off-line. We propose a theoretical model of the residual
laser noise including this flexing-filtering coupling. We also use two
independent simulators to produce realistic measurement signals and compute the
corresponding TDI Michelson variables. We show that our theoretical model
agrees with the simulated data with exquisite precision. Using these two
complementary approaches, we confirm TDI's ability to reduce laser frequency
noise in a more realistic mission setup. The theoretical model provides insight
on filter design and implementation. | astro-ph_IM |
The BlueMUSE data reduction pipeline: lessons learned from MUSE and
first design choices: BlueMUSE is an integral field spectrograph in an early development stage for
the ESO VLT. For our design of the data reduction software for this instrument,
we are first reviewing capabilities and issues of the pipeline of the existing
MUSE instrument. MUSE has been in operation at the VLT since 2014 and led to
discoveries published in more than 600 refereed scientific papers. While
BlueMUSE and MUSE have many common properties we briefly point out a few key
differences between both instruments. We outline a first version of the
flowchart for the science reduction, and discuss the necessary changes due to
the blue wavelength range covered by BlueMUSE. We also detail specific new
features, for example, how the pipeline and subsequent analysis will benefit
from improved handling of the data covariance, and a more integrated approach
to the line-spread function, as well as improvements regarding the wavelength
calibration which is of extra importance in the blue optical range. We finally
discuss how simulations of BlueMUSE datacubes are being implemented and how
they will be used to prepare the science of the instrument. | astro-ph_IM |
Ground-based gamma-ray telescopes as ground stations in deep-space
lasercom: As the amount of information to be transmitted from deep-space rapidly
increases, the radiofrequency technology has become a bottleneck in space
communications. RF is already limiting the scientific outcome of deep-space
missions and could be a significant obstacle in the developing of manned
missions. Lasercom holds the promise to solve this problem, as it will
considerably increase the data rate while decreasing the energy, mass and
volume of onboard communication systems. In RF deep-space communications, where
the received power is the main limitation, the traditional approach to boost
the data throughput has been increasing the receiver's aperture, e.g. the 70-m
antennas in the NASA's Deep Space Network. Optical communications also can
benefit from this strategy, thus 10-m class telescopes have typically been
suggested to support future deep-space links. However, the cost of big
telescopes increase exponentially with their aperture, and new ideas are needed
to optimize this ratio. Here, the use of ground-based gamma-ray telescopes,
known as Cherenkov telescopes, is suggested. These are optical telescopes
designed to maximize the receiver's aperture at a minimum cost with some
relaxed requirements. As they are used in an array configuration and multiple
identical units need to be built, each element of the telescope is designed to
minimize its cost. Furthermore, the native array configuration would facilitate
the joint operation of Cherenkov and lasercom telescopes. These telescopes
offer very big apertures, ranging from several meters to almost 30 meters,
which could greatly improve the performance of optical ground stations. The key
elements of these telescopes have been studied applied to lasercom, reaching
the conclusion that it could be an interesting strategy to include them in the
future development of an optical deep-space network. | astro-ph_IM |
Characterization of a dense aperture array for radio astronomy: EMBRACE@Nancay is a prototype instrument consisting of an array of 4608
densely packed antenna elements creating a fully sampled, unblocked aperture.
This technology is proposed for the Square Kilometre Array and has the
potential of providing an extremely large field of view making it the ideal
survey instrument. We describe the system,calibration procedures, and results
from the prototype. | astro-ph_IM |
(Very)-High-Energy Gamma-Ray Astrophysics: the Future: Several projects planned or proposed can significantly expand our knowledge
of the high-energy Universe in gamma rays. Construction of the Cherenkov
telescope array CTA is started, and other detectors are planned which will use
the reconstruction of extensive air showers. This report explores the near
future, and possible evolutions in a longer term. | astro-ph_IM |
Importance of charge capture in inter-phase regions during readout of
charge-coupled devices: The current understanding of charge transfer dynamics in Charge-Coupled
Devices (CCDs) is that charge is moved so quickly from one phase to the next in
a clocking sequence and with a density so low that trapping of charge in the
inter-phase regions is negligible. However, new simulation capabilities
developed at the Centre for Electronic Imaging, that includes direct input of
electron density simulations, has made it possible to investigate this
assumption further. As part of the radiation testing campaign of the Euclid
CCD273 devices, data has been obtained using the trap pumping method, that can
be used to identify and characterise single defects CCDs. Combining this data
with simulations, we find that trapping during the transfer of charge between
phases is indeed necessary in order to explain the results of the data
analysis. This result could influence not only trap pumping theory and how trap
pumping should be performed, but also how a radiation damaged CCD is read out
in the most optimal way. | astro-ph_IM |
Spectral and polarimetric characterization of the Gas Pixel Detector
filled with dimethyl ether: The Gas Pixel Detector belongs to the very limited class of gas detectors
optimized for the measurement of X-ray polarization in the emission of
astrophysical sources. The choice of the mixture in which X-ray photons are
absorbed and photoelectrons propagate, deeply affects both the energy range of
the instrument and its performance in terms of gain, track dimension and
ultimately, polarimetric sensitivity. Here we present the characterization of
the Gas Pixel Detector with a 1 cm thick cell filled with dimethyl ether (DME)
at 0.79 atm, selected among other mixtures for the very low diffusion
coefficient. Almost completely polarized and monochromatic photons were
produced at the calibration facility built at INAF/IASF-Rome exploiting Bragg
diffraction at nearly 45 degrees. For the first time ever, we measured the
modulation factor and the spectral capabilities of the instrument at energies
as low as 2.0 keV, but also at 2.6 keV, 3.7 keV, 4.0 keV, 5.2 keV and 7.8 keV.
These measurements cover almost completely the energy range of the instrument
and allows to compare the sensitivity achieved with that of the standard
mixture, composed of helium and DME. | astro-ph_IM |
X-ray Astronomy in the Laboratory with a Miniature Compact Object
Produced by Laser-Driven Implosion: Laboratory spectroscopy of non-thermal equilibrium plasmas photoionized by
intense radiation is a key to understanding compact objects, such as black
holes, based on astronomical observations. This paper describes an experiment
to study photoionizing plasmas in laboratory under well-defined and genuine
conditions. Photoionized plasma is here generated using a 0.5-keV Planckian
x-ray source created by means of a laser-driven implosion. The measured x-ray
spectrum from the photoionized silicon plasma resembles those observed from the
binary stars Cygnus X-3 and Vela X-1 with the Chandra x-ray satellite. This
demonstrates that an extreme radiation field was produced in the laboratory,
however, the theoretical interpretation of the laboratory spectrum
significantly contradicts the generally accepted explanations in x-ray
astronomy. This model experiment offers a novel test bed for validation and
verification of computational codes used in x-ray astronomy. | astro-ph_IM |
Robust period estimation using mutual information for multi-band light
curves in the synoptic survey era: The Large Synoptic Survey Telescope (LSST) will produce an unprecedented
amount of light curves using six optical bands. Robust and efficient methods
that can aggregate data from multidimensional sparsely-sampled time series are
needed. In this paper we present a new method for light curve period estimation
based on the quadratic mutual information (QMI). The proposed method does not
assume a particular model for the light curve nor its underlying probability
density and it is robust to non-Gaussian noise and outliers. By combining the
QMI from several bands the true period can be estimated even when no
single-band QMI yields the period. Period recovery performance as a function of
average magnitude and sample size is measured using 30,000 synthetic multi-band
light curves of RR Lyrae and Cepheid variables generated by the LSST Operations
and Catalog simulators. The results show that aggregating information from
several bands is highly beneficial in LSST sparsely-sampled time series,
obtaining an absolute increase in period recovery rate up to 50%. We also show
that the QMI is more robust to noise and light curve length (sample size) than
the multiband generalizations of the Lomb Scargle and Analysis of Variance
periodograms, recovering the true period in 10-30% more cases than its
competitors. A python package containing efficient Cython implementations of
the QMI and other methods is provided. | astro-ph_IM |
The PAU Survey: Narrow-band image photometry: PAUCam is an innovative optical narrow-band imager mounted at the William
Herschel Telescope built for the Physics of the Accelerating Universe Survey
(PAUS). Its set of 40 filters results in images that are complex to calibrate,
with specific instrumental signatures that cannot be processed with traditional
data reduction techniques. In this paper we present two pipelines developed by
the PAUS data management team with the objective of producing science-ready
catalogues from the uncalibrated raw images. The Nightly pipeline takes care of
all image processing, with bespoke algorithms for photometric calibration and
scatter-light correction. The Multi-Epoch and Multi-Band Analysis (MEMBA)
pipeline performs forced photometry over a reference catalogue to optimize the
photometric redshift performance. We verify against spectroscopic observations
that the current approach delivers an inter-band photometric calibration of
0.8% across the 40 narrow-band set. The large volume of data produced every
night and the rapid survey strategy feedback constraints require operating both
pipelines in the Port d'Informaci\'o Cientifica data centre with intense
parallelization. While alternative algorithms for further improvements in
photo-z performance are under investigation, the image calibration and
photometry presented in this work already enable state-of-the-art photometric
redshifts down to iAB=23.0. | astro-ph_IM |
The design of the Ali CMB Polarization Telescope receiver: Ali CMB Polarization Telescope (AliCPT-1) is the first CMB degree-scale
polarimeter to be deployed on the Tibetan plateau at 5,250m above sea level.
AliCPT-1 is a 90/150 GHz 72 cm aperture, two-lens refracting telescope cooled
down to 4 K. Alumina lenses, 800mm in diameter, image the CMB in a 33.4{\deg}
field of view on a 636mm wide focal plane. The modularized focal plane consists
of dichroic polarization-sensitive Transition-Edge Sensors (TESes). Each module
includes 1,704 optically active TESes fabricated on a 150mm diameter silicon
wafer. Each TES array is read out with a microwave multiplexing readout system
capable of a multiplexing factor up to 2,048. Such a large multiplexing factor
has allowed the practical deployment of tens of thousands of detectors,
enabling the design of a receiver that can operate up to 19 TES arrays for a
total of 32,376 TESes. AliCPT-1 leverages the technological advancements in the
detector design from multiple generations of previously successful
feedhorn-coupled polarimeters, and in the instrument design from BICEP-3, but
applied on a larger scale. The cryostat receiver is currently under integration
and testing. During the first deployment year, the focal plane will be
populated with up to 4 TES arrays. Further TES arrays will be deployed in the
following years, fully populating the focal plane with 19 arrays on the fourth
deployment year. Here we present the AliCPT-1 receiver design, and how the
design has been optimized to meet the experimental requirements. | astro-ph_IM |
BATATA: A device to characterize the punch-through observed in
underground muon detectors and to operate as a prototype for AMIGA: BATATA is a hodoscope comprising three X-Y planes of plastic scintillation
detectors. This system of buried counters is complemented by an array of 3
water-Cherenkov detectors, located at the vertices of an equilateral triangle
with 200 m sides. This small surface array is triggered by extensive air
showers. The BATATA detector will be installed at the centre of the AMIGA
array, where it will be used to quantify the electromagnetic contamination of
the muon signal as a function of depth, and so to validate, in situ, the
numerical estimates made of the optimal depth for the AMIGA muon detectors.
BATATA will also serves as a prototype to aid the design of these detectors. | astro-ph_IM |
DIPol-UF: simultaneous three-color ($BVR$) polarimeter with EM CCDs: We describe a new instrument capable of high precision ($10^{-5}$)
polarimetric observations simultaneously in three passbands ($BVR$). The
instrument utilizes electron-multiplied EM CCD cameras for high efficiency and
fast image readout. The key features of DIPol-UF are: (i) optical design with
high throughput and inherent stability; (ii) great versatility which makes the
instrument optimally suitable for observations of bright and faint targets;
(iii) control system which allows using the polarimeter remotely. Examples are
given of the first results obtained from high signal-to-noise observations of
bright nearby stars and of fainter sources such as X-ray binaries in their
quiescent states | astro-ph_IM |
QUBIC V: Cryogenic system design and performance: Current experiments aimed at measuring the polarization of the Cosmic
Microwave Background (CMB) use cryogenic detector arrays and cold optical
systems to boost the mapping speed of the sky survey. For these reasons, large
volume cryogenic systems, with large optical windows, working continuously for
years, are needed. Here we report on the cryogenic system of the QUBIC (Q and U
Bolometric Interferometer for Cosmology) experiment: we describe its design,
fabrication, experimental optimization and validation in the Technological
Demonstrator configuration. The QUBIC cryogenic system is based on a large
volume cryostat, using two pulse-tube refrigerators to cool at ~3K a large (~1
m^3) volume, heavy (~165kg) instrument, including the cryogenic polarization
modulator, the corrugated feedhorns array, and the lower temperature stages; a
4He evaporator cooling at ~1K the interferometer beam combiner; a 3He
evaporator cooling at ~0.3K the focal-plane detector arrays. The cryogenic
system has been tested and validated for more than 6 months of continuous
operation. The detector arrays have reached a stable operating temperature of
0.33K, while the polarization modulator has been operated from a ~10K base
temperature. The system has been tilted to cover the boresight elevation range
20 deg -90 deg without significant temperature variations. The instrument is
now ready for deployment to the high Argentinean Andes. | astro-ph_IM |
Inferring kilonova population properties with a hierarchical Bayesian
framework I : Non-detection methodology and single-event analyses: We present ${\tt nimbus}$ : a hierarchical Bayesian framework to infer the
intrinsic luminosity parameters of kilonovae (KNe) associated with
gravitational-wave (GW) events, based purely on non-detections. This framework
makes use of GW 3-D distance information and electromagnetic upper limits from
multiple surveys for multiple events, and self-consistently accounts for finite
sky-coverage and probability of astrophysical origin. The framework is agnostic
to the brightness evolution assumed and can account for multiple
electromagnetic passbands simultaneously. Our analyses highlight the importance
of accounting for model selection effects, especially in the context of
non-detections. We show our methodology using a simple, two-parameter linear
brightness model, taking the follow-up of GW190425 with the Zwicky Transient
Facility (ZTF) as a single-event test case for two different prior choices of
model parameters -- (i) uniform/uninformative priors and (ii) astrophysical
priors based on surrogate models of Monte Carlo radiative transfer simulations
of KNe. We present results under the assumption that the KN is within the
searched region to demonstrate functionality and the importance of prior
choice. Our results show consistency with ${\tt simsurvey}$ -- an astronomical
survey simulation tool used previously in the literature to constrain the
population of KNe. While our results based on uniform priors strongly constrain
the parameter space, those based on astrophysical priors are largely
uninformative, highlighting the need for deeper constraints. Future studies
with multiple events having electromagnetic follow-up from multiple surveys
should make it possible to constrain the KN population further. | astro-ph_IM |
EAGLE Spectroscopy of Resolved Stellar Populations Beyond the Local
Group: We give an overview of the science case for spectroscopy of resolved stellar
populations beyond the Local Group with the European Extremely Large Telescope
(E-ELT). In particular, we present science simulations undertaken as part of
the EAGLE Phase A design study for a multi--integral-field-unit, near-infrared
spectrograph. EAGLE will exploit the unprecedented primary aperture of the
E-ELT to deliver AO-corrected spectroscopy across a large (38.5 sq. arcmin)
field, truly revolutionising our view of stellar populations in the Local
Volume. | astro-ph_IM |
How to Calculate Molecular Column Density: The calculation of the molecular column density from molecular spectral
(rotational or ro-vibrational) transition measurements is one of the most basic
quantities derived from molecular spectroscopy. Starting from first principles
where we describe the basic physics behind the radiative and collisional
excitation of molecules and the radiative transfer of their emission, we derive
a general expression for the molecular column density. As the calculation of
the molecular column density involves a knowledge of the molecular energy level
degeneracies, rotational partition functions, dipole moment matrix elements,
and line strengths, we include generalized derivations of these
molecule-specific quantities. Given that approximations to the column density
equation are often useful, we explore the optically thin, optically thick, and
low-frequency limits to our derived general molecular column density relation.
We also evaluate the limitations of the common assumption that the molecular
excitation temperature is constant, and address the distinction between beam-
and source-averaged column densities. We conclude our discussion of the
molecular column density with worked examples for C$^{18}$O, C$^{17}$O,
N$_2$H$^+$, NH$_3$, and H$_2$CO. Ancillary information on some subtleties
involving line profile functions, conversion between integrated flux and
brightness temperature, the calculation of the uncertainty associated with an
integrated intensity measurement, the calculation of spectral line optical
depth using hyperfine or isotopologue measurements, the calculation of the
kinetic temperature from a symmetric molecule excitation temperature
measurement, and relative hyperfine intensity calculations for NH$_3$ are
presented in appendices. The intent of this document is to provide a reference
for researchers studying astrophysical molecular spectroscopic measurements. | astro-ph_IM |
Faint objects in motion: the new frontier of high precision astrometry: Sky survey telescopes and powerful targeted telescopes play complementary
roles in astronomy. In order to investigate the nature and characteristics of
the motions of very faint objects, a flexibly-pointed instrument capable of
high astrometric accuracy is an ideal complement to current astrometric surveys
and a unique tool for precision astrophysics. Such a space-based mission will
push the frontier of precision astrometry from evidence of Earth-mass habitable
worlds around the nearest stars, to distant Milky Way objects, and out to the
Local Group of galaxies. As we enter the era of the James Webb Space Telescope
and the new ground-based, adaptive-optics-enabled giant telescopes, by
obtaining these high precision measurements on key objects that Gaia could not
reach, a mission that focuses on high precision astrometry science can
consolidate our theoretical understanding of the local Universe, enable
extrapolation of physical processes to remote redshifts, and derive a much more
consistent picture of cosmological evolution and the likely fate of our cosmos.
Already several missions have been proposed to address the science case of
faint objects in motion using high precision astrometry missions: NEAT proposed
for the ESA M3 opportunity, micro-NEAT for the S1 opportunity, and Theia for
the M4 and M5 opportunities. Additional new mission configurations adapted with
technological innovations could be envisioned to pursue accurate measurements
of these extremely small motions. The goal of this White Paper is to address
the fundamental science questions that are at stake when we focus on the
motions of faint sky objects and to briefly review instrumentation and mission
profiles. | astro-ph_IM |
Towards Extremely Precise Radial Velocities: I. Simulated Solar Spectra
for Testing Exoplanet Detection Algorithms: Recent and upcoming stabilized spectrographs are pushing the frontier for
Doppler spectroscopy to detect and characterize low-mass planets.
Specifications for these instruments are so impressive that intrinsic stellar
variability is expected to limit their Doppler precision for most target stars
(Fischer et al. 2016). To realize their full potential, astronomers must
develop new strategies for distinguishing true Doppler shifts from intrinsic
stellar variability. Stellar variability due to star spots, faculae and other
rotationally-linked variability are particularly concerning, as the stellar
rotation period is often included in the range of potential planet orbital
periods. To robustly detect and accurately characterize low-mass planets via
Doppler planet surveys, the exoplanet community must develop statistical models
capable of jointly modeling planetary perturbations and intrinsic stellar
variability. Towards this effort, this note presents simulations of extremely
high resolution, solar-like spectra created with SOAP 2.0 (arXiv:1409.3594)
that includes multiple evolving star spots. We anticipate this data set will
contribute to future studies developing, testing, and comparing statistical
methods for measuring physical radial velocities amid contamination by stellar
variability. | astro-ph_IM |
The CASA software for radio astronomy: status update from ADASS 2019: CASA, the Common Astronomy Software Applications package, is the primary data
processing software for the Atacama Large Millimeter/submillimeter Array (ALMA)
and NSF's Karl G. Jansky Very Large Array (VLA), and is frequently used also
for other radio telescopes. The CASA software can process data from both
single-dish and aperture-synthesis telescopes, and one of its core
functionalities is to support the data reduction and imaging pipelines for
ALMA, VLA and the VLA Sky Survey (VLASS). CASA has recently undergone several
exciting new developments, including an increased flexibility in Python (CASA
6), support of Very Long Baseline Interferometry (VLBI), performance gains
through parallel imaging, data visualization with the new Cube Analysis
Rendering Tool for Astronomy (CARTA), enhanced reliability and testing, and
modernized documentation. These proceedings of the 2019 Astronomical Data
Analysis Software & Systems (ADASS) conference give an update of the CASA
project, and detail how these new developments will enhance user experience of
CASA. | astro-ph_IM |
A dipole amplifier for electric dipole moments, axion-like particles and
a dense dark matter hairs detector: A tool that can constrain, in minutes, beyond-the-standard-model parameters
like electric dipole moments (EDM) down to a lower-bound
$d_\text{e}^{\cal{N}}<10^{-37}\text{e}\cdot\text{cm}$ in bulk materials, or the
coupling of axion-like particles (ALP) to photons down to
$|G_{a\gamma\gamma}|<10^{-16}$~GeV$^{-1}$, is described. Best limits are
$d^n_e<3\cdot10^{-26}\text{e}\cdot\text{cm}$ for neutron EDM and
$|G_{a\gamma\gamma}|<6.6\cdot10^{-11}$~GeV$^{-1}$. The {\it dipole amplifier}
is built from a superconducting loop immersed in a toroidal magnetic field,
$\vec{B}$. When nuclear magnetic moments in the London penetration depth align
with $\vec{B}$, the bulk magnetization is always accompanied by an EDM-induced
bulk electric field $\vec{E}\propto\vec{B}$ that generates detectable
oscillatory supercurrents with a characteristic frequency
$\omega_{\text{D}}\propto d_\text{e}^{\cal{N}}$. Cold dark matter (CDM) ALP are
formally similar where $\omega_\text{D}\propto
|G_{a\gamma\gamma}|\sqrt{n_a/(2m_a)}$ with $m_a$ the ALP mass and $n_a$ its
number density. A space probe traversing a dark matter hair with a dipole
amplifier is sensitive enough to detect ALP density variations if
$|G_{a\gamma\gamma}|\sqrt{n_h/(2m_a)}>4.9\cdot10^{-27}$ where $n_h$ is the ALP
number density in the hair. | astro-ph_IM |
Generating Electron Beam Lithography Write Parameters from the FORTIS
Holographic Grating Solution: The Far-UV Off Rowland-circle Telescope for Imaging and Spectroscopy (FORTIS)
has been successful in maturing technologies for carrying out multi-object
spectroscopy in the far-UV, including: the successful implementation of the
Next Generation of Microshutter Arrays; large-area microchannel plate
detectors; and an aspheric "dual-order" holographically ruled diffraction
grating with curved, variably-spaced grooves with a laminar (rectangular)
profile. These optical elements were used to construct an efficient and
minimalist "two-bounce" spectro-telescope in a Gregorian configuration.
However, the susceptibility to Lyman alpha (Ly$\alpha$) scatter inherent to the
dual order design has been found to be intractably problematic, motivating our
move to an "Off-Axis" design. OAxFORTIS will mitigate its susceptibility to
Ly$\alpha$ by enclosing the optical path, so the detector only receives light
from the grating. The new design reduces the collecting area by a factor of 2,
but the overall effective area can be regained and improved through the use of
new high efficiency reflective coatings, and with the use of a blazed
diffraction grating. This latter key technology has been enabled by recent
advancements in creating very high efficiency blazed gratings with impressive
smoothness using electron beam lithography and chemical etching to create
grooves in crystalline silicon. Here we discuss the derivation for the
OAxFORTIS grating solution as well as methods used to transform the FORTIS
holographic grating recording parameters (following the formalism of Noda et
al.1974a,b), into curved and variably-spaced rulings required to drive the
electron beam lithography write-head in three dimensions. We will also discuss
the process for selecting silicon wafers with the proper orientation of the
crystalline planes and give an update on our fabrication preparations. | astro-ph_IM |
A detection system to measure muon-induced neutrons for direct Dark
Matter searches: Muon-induced neutrons constitute a prominent background component in a number
of low count rate experiments, namely direct searches for Dark Matter. In this
work we describe a neutron detector to measure this background in an
underground laboratory, the Laboratoire Souterrain de Modane. The system is
based on 1 m3 of Gd-loaded scintillator and it is linked with the muon veto of
the EDELWEISS-II experiment for coincident muon detection. The system was
installed in autumn 2008 and passed since then a number of commissioning tests
proving its full functionality. The data-taking is continuously ongoing and a
count rate of the order of 1 muon-induced neutron per day has been achieved. | astro-ph_IM |
Automatic quantitative morphological analysis of interacting galaxies: The large number of galaxies imaged by digital sky surveys reinforces the
need for computational methods for analyzing galaxy morphology. While the
morphology of most galaxies can be associated with a stage on the Hubble
sequence, morphology of galaxy mergers is far more complex due to the
combination of two or more galaxies with different morphologies and the
interaction between them. Here we propose a computational method based on
unsupervised machine learning that can quantitatively analyze morphologies of
galaxy mergers and associate galaxies by their morphology. The method works by
first generating multiple synthetic galaxy models for each galaxy merger, and
then extracting a large set of numerical image content descriptors for each
galaxy model. These numbers are weighted using Fisher discriminant scores, and
then the similarities between the galaxy mergers are deduced using a variation
of Weighted Nearest Neighbor analysis such that the Fisher scores are used as
weights. The similarities between the galaxy mergers are visualized using
phylogenies to provide a graph that reflects the morphological similarities
between the different galaxy mergers, and thus quantitatively profile the
morphology of galaxy mergers. | astro-ph_IM |
Refine Neutrino Events Reconstruction with BEiT-3: Neutrino Events Reconstruction has always been crucial for IceCube Neutrino
Observatory. In the Kaggle competition "IceCube -- Neutrinos in Deep Ice", many
solutions use Transformer. We present ISeeCube, a pure Transformer model based
on TorchScale (the backbone of BEiT-3). When having relatively same amount of
total trainable parameters, our model outperforms the 2nd place solution. By
using TorchScale, the lines of code drop sharply by about 80% and a lot of new
methods can be tested by simply adjusting configs. We compared two fundamental
models for predictions on a continuous space, regression and classification,
trained with MSE Loss and CE Loss respectively. We also propose a new metric,
overlap ratio, to evaluate the performance of the model. Since the model is
simple enough, it has the potential to be used for more purposes such as energy
reconstruction, and many new methods such as combining it with GraphNeT can be
tested more easily. The code and pretrained models are available at
https://github.com/ChenLi2049/ISeeCube | astro-ph_IM |
Understanding our Galaxy - key contributions from the Parkes telescope: Young massive stars, with their spectacular masers and HII regions, dominate
our Galaxy, and are a cornerstone for understanding Galactic structure. I will
highlight the role of Parkes in contributing to these studies - past, present
and future. | astro-ph_IM |
Summary of the 14th IACHEC Meeting: We summarize the 14th meeting of the International Astronomical Consortium
for High Energy Calibration (IACHEC) held at \textit{Shonan Village} (Kanagawa,
Japan) in May 2019. Sixty scientists directly involved in the calibration of
operational and future high-energy missions gathered during 3.5 days to discuss
the status of the cross-calibration between the current international
complement of X-ray observatories, and the possibilities to improve it. This
summary consists of reports from the various WGs with topics ranging from the
identification and characterization of standard calibration sources,
multi-observatory cross-calibration campaigns, appropriate and new statistical
techniques, calibration of instruments and characterization of background,
communication and preservation of knowledge, and results for the benefit of the
astronomical community. | astro-ph_IM |
On-sky validation of image-based adaptive optics wavefront sensor
referencing: Differentiating between an exoplanet signal and residual speckle noise is a
key challenge in high-contrast imaging. Speckles are due to a combination of
fast, slow and static wavefront aberrations introduced by atmospheric
turbulence and instrument optics. While wavefront control techniques developed
over the last decade have shown promise in minimizing fast atmospheric
residuals, slow and static aberrations such as non-common path aberrations
(NCPAs) remain a key limiting factor for exoplanet detection. NCPA are not seen
by the wavefront sensor (WFS) of the adaptive optics (AO) loop, hence the
difficulty in correcting them. We propose to improve the identification and
rejection of those aberrations. The algorithm DrWHO, performs frequent
compensation of static and quasi-static aberrations to boost image contrast. By
changing the WFS reference at every iteration of the algorithm, DrWHO changes
the AO point of convergence to lead it towards a compensation of the static and
slow aberrations. References are calculated using an iterative lucky-imaging
approach, where each iteration updates the WFS reference, ultimately favoring
high-quality focal plane images. We validate this concept through numerical
simulations and on-sky testing on the SCExAO instrument at the 8.2-m Subaru
telescope. Simulations show a rapid convergence towards the correction of 82%
of the NCPAs. On-sky tests are performed over a 10-minute run in the visible
(750 nm). We introduce a flux concentration (FC) metric to quantify the point
spread function (PSF) quality and measure a 15.7% improvement. The DrWHO
algorithm is a robust focal-plane wavefront sensing calibration method that has
been successfully demonstrated on sky. It does not rely on a model nor requires
wavefront sensor calibration or linearity. It is compatible with different
wavefront control methods, and can be further optimized for speed and
efficiency. | astro-ph_IM |
DESCQA: An Automated Validation Framework for Synthetic Sky Catalogs: The use of high-quality simulated sky catalogs is essential for the success
of cosmological surveys. The catalogs have diverse applications, such as
investigating signatures of fundamental physics in cosmological observables,
understanding the effect of systematic uncertainties on measured signals and
testing mitigation strategies for reducing these uncertainties, aiding analysis
pipeline development and testing, and survey strategy optimization. The list of
applications is growing with improvements in the quality of the catalogs and
the details that they can provide. Given the importance of simulated catalogs,
it is critical to provide rigorous validation protocols that enable both
catalog providers and users to assess the quality of the catalogs in a
straightforward and comprehensive way. For this purpose, we have developed the
DESCQA framework for the Large Synoptic Survey Telescope Dark Energy Science
Collaboration as well as for the broader community. The goal of DESCQA is to
enable the inspection, validation, and comparison of an inhomogeneous set of
synthetic catalogs via the provision of a common interface within an automated
framework. In this paper, we present the design concept and first
implementation of DESCQA. In order to establish and demonstrate its full
functionality we use a set of interim catalogs and validation tests. We
highlight several important aspects, both technical and scientific, that
require thoughtful consideration when designing a validation framework,
including validation metrics and how these metrics impose requirements on the
synthetic sky catalogs. | astro-ph_IM |
Measurement of low-energy background events due to $^{222}$Rn
contamination on the surface of a NaI(Tl) crystal: It has been known that decays of daughter elements of $^{222}$Rn on the
surface of a detector cause significant background at energies below 10 keV. In
particular $^{210}$Pb and $^{210}$Po decays on the crystal surface result in
significant background for dark matter search experiments with NaI(Tl)
crystals. In this report, measurement of $^{210}$Pb and $^{210}$Po decays on
surfaces are obtained by using a $^{222}$Rn contaminated crystal. Alpha decay
events of $^{210}$Po on the surface are measured by coincidence requirements of
two attached crystals. Due to recoiling of $^{206}$Pb, rapid nuclear recoil
events are observed. A mean time characterization demonstrates that $^{206}$Pb
recoil events can be statistically separated from those of sodium or iodine
nuclear recoil events, as well as electron recoil events. | astro-ph_IM |
Daytime Seeing and Solar Limb Positions: A method to measure the seeing from video made during drift-scan solar
transits is proposed. The limb of the Sun is projected over a regular grid
evenly spaced. The temporal dispersion of the time intervals among the contacts
between solar limb and grid's rows is proportional to the atmospheric seeing.
Seeing effects on the position of the inflexion point of the limb's luminosity
profile are calculated numerically with Fast Fourier Transform. Observational
examples from Locarno and Paris Observatories are presented to show the
asymmetric contributions of the seeing at the beginning and the end of each
drift-scan transit. | astro-ph_IM |
Gravitational Microlensing Events as a Target for SETI project: Detection of signals from a possible extrasolar technological civilization is
one of the challenging efforts of science. In this work, we propose using
natural telescopes made of single or binary gravitational lensing systems to
magnify leakage of electromagnetic signals from a remote planet harbours an
Extra Terrestrial Intelligent (ETI) technology. The gravitational microlensing
surveys are monitoring a large area of Galactic bulge for searching
microlensing events and they find more than $2000$ events per year. These
lenses are capable of playing the role of natural telescopes and in some
occasions they can magnify radio band signals from the planets orbiting around
the source stars in gravitational microlensing systems. Assuming that frequency
of electromagnetic waves used for telecommunication in ETIs is similar to ours,
we propose follow-up observation of microlensing events with radio telescopes
such as Square Kilometre Array (SKA), Low Frequency Demonstrators (LFD) and
Mileura Wide-Field Array (MWA). Amplifying signals from the leakage of
broadcasting by an Earth-like civilizations will allow us to detect them up to
center of Milky Way galaxy. Our analysis shows that in binary microlensing
systems, the probability of amplification of signals from ETIs is more than
that in single microlensing events. Finally we propose target of opportunity
mode for follow-up observations of binary microlensing events with SKA as a new
observational program for searching ETIs. Using the optimistic values for the
factors of Drake equation provides detection of about one event per year. | astro-ph_IM |
Probing Radio Intensity at high-Z from Marion: 2017 Instrument: We introduce Probing Radio Intensity at high-Z from Marion (PRIZM), a new
experiment designed to measure the globally averaged sky brightness, including
the expected redshifted 21 cm neutral hydrogen absorption feature arising from
the formation of the first stars. PRIZM consists of two dual-polarization
antennas operating at central frequencies of 70 and 100 MHz, and the experiment
is located on Marion Island in the sub-Antarctic. We describe the initial
design and configuration of the PRIZM instrument that was installed in 2017,
and we present preliminary data that demonstrate that Marion Island offers an
exceptionally clean observing environment, with essentially no visible
contamination within the FM band. | astro-ph_IM |
Improved Measurement of the Spectral Index of the Diffuse Radio
Background Between 90 and 190 MHz: We report absolutely calibrated measurements of diffuse radio emission
between 90 and 190 MHz from the Experiment to Detect the Global EoR Signature
(EDGES). EDGES employs a wide beam zenith-pointing dipole antenna centred on a
declination of -26.7$^\circ$. We measure the sky brightness temperature as a
function of frequency averaged over the EDGES beam from 211 nights of data
acquired from July 2015 to March 2016. We derive the spectral index, $\beta$,
as a function of local sidereal time (LST) and find -2.60 > $\beta$ > -2.62
$\pm$0.02 between 0 and 12 h LST. When the Galactic Centre is in the sky, the
spectral index flattens, reaching $\beta$ = -2.50 $\pm$0.02 at 17.7 h. The
EDGES instrument is shown to be very stable throughout the observations with
night-to-night reproducibility of $\sigma_{\beta}$ < 0.003. Including
systematic uncertainty, the overall uncertainty of $\beta$ is 0.02 across all
LST bins. These results improve on the earlier findings of Rogers & Bowman
(2008) by reducing the spectral index uncertainty from 0.10 to 0.02 while
considering more extensive sources of errors. We compare our measurements with
spectral index simulations derived from the Global Sky Model (GSM) of de
Oliveira-Costa et al. (2008) and with fits between the Guzm\'an et al. (2011)
45 MHz and Haslam et al. (1982) 408 MHz maps. We find good agreement at the
transit of the Galactic Centre. Away from transit, the GSM tends to
over-predict (GSM less negative) by 0.05 < $\Delta_{\beta} =
\beta_{\text{GSM}}-\beta_{\text{EDGES}}$ < 0.12, while the 45-408 MHz fits tend
to over-predict by $\Delta_{\beta}$ < 0.05. | astro-ph_IM |
Auto-RSM: an automated parameter-selection algorithm for the RSM map
exoplanet detection algorithm: Most of the high-contrast imaging (HCI) data-processing techniques used over
the last 15 years have relied on the angular differential imaging (ADI)
observing strategy, along with subtraction of a reference point spread function
(PSF) to generate exoplanet detection maps. Recently, a new algorithm called
regime switching model (RSM) map has been proposed to take advantage of these
numerous PSF-subtraction techniques; RSM uses several of these techniques to
generate a single probability map. Selection of the optimal parameters for
these PSF-subtraction techniques as well as for the RSM map is not
straightforward, is time consuming, and can be biased by assumptions made as to
the underlying data set. We propose a novel optimisation procedure that can be
applied to each of the PSF-subtraction techniques alone, or to the entire RSM
framework. The optimisation procedure consists of three main steps: (i)
definition of the optimal set of parameters for the PSF-subtraction techniques
using the contrast as performance metric, (ii) optimisation of the RSM
algorithm, and (iii) selection of the optimal set of PSF-subtraction techniques
and ADI sequences used to generate the final RSM probability map. The
optimisation procedure is applied to the data sets of the exoplanet imaging
data challenge (EIDC), which provides tools to compare the performance of HCI
data-processing techniques. The data sets consist of ADI sequences obtained
with three state-of-the-art HCI instruments: SPHERE, NIRC2, and LMIRCam. The
results of our analysis demonstrate the interest of the proposed optimisation
procedure, with better performance metrics compared to the earlier version of
RSM, as well as to other HCI data-processing techniques. | astro-ph_IM |
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