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On discrepancy between ATIC and Fermi data: Either ATIC or Fermi-LAT data can be fitted together with the PAMELA data by
three components: primary background ~ E^{-3.3}, secondary background ~
E^{-3.6}, and an additional source of electrons ~ E^{-g_a} Exp(-E/E_{cut}). We
find that the best fits for ATIC + PAMELA and for Fermi + PAMELA are
approximately the same, g_a ~ 2 and E_{cut} ~ 500 GeV. However, the ATIC data
have a narrow bump between 300 GeV and 600 GeV which contradicts the smooth
Fermi spectrum. An interpretation of the ATIC bump as well as the featureless
Fermi spectrum in terms of dark matter models and pulsars is discussed. | astro-ph_HE |
The Morphologies and Kinematics of Supernova Remnants: We review the major advances in understanding the morphologies and kinematics
of supernova remnants (SNRs). Simulations of SN explosions have improved
dramatically over the last few years, and SNRs can be used to test models
through comparison of predictions with SNRs' observed large-scale compositional
and morphological properties as well as the three-dimensional kinematics of
ejecta material. In particular, Cassiopeia A -- the youngest known
core-collapse SNR in the Milky Way -- offers an up-close view of the complexity
of these explosive events that cannot be resolved in distant, extragalactic
sources. We summarize the progress in tying SNRs to their progenitors'
explosions through imaging and spectroscopic observations, and we discuss
exciting future prospects for SNR studies, such as X-ray microcalorimeters | astro-ph_HE |
Spectral and Timing Properties of IGR J17091-3624 in the Rising Hard
State During its 2016 Outburst: We present a spectral and timing study of the NuSTAR and Swift observations
of the black hole candidate IGR J17091-3624 in the hard state during its
outburst in 2016. Disk reflection is detected in each of the NuSTAR spectra
taken in three epochs. Fitting with relativistic reflection models reveals that
the accretion disk is truncated during all epochs with $R_{\rm in}>10~r_{\rm
g}$, with the data favoring a low disk inclination of $\sim
30^{\circ}-40^{\circ}$. The steepening of the continuum spectra between epochs
is accompanied by a decrease in the high energy cut-off: the electron
temperature $kT_{\rm e}$ drops from $\sim 64$ keV to $\sim 26$ keV, changing
systematically with the source flux. We detect type-C QPOs in the power spectra
with frequency varying between 0.131 Hz and 0.327 Hz. In addition, a secondary
peak is found in the power spectra centered at about 2.3 times the QPO
frequency during all three epochs. The nature of this secondary frequency is
uncertain, however a non-harmonic origin is favored. We investigate the
evolution of the timing and spectral properties during the rising phase of the
outburst and discuss their physical implications. | astro-ph_HE |
An unexpected drop in the magnetic field of the X-ray pulsar V0332+53
after the bright outburst occurred in 2015: How the accreted mass settling on the surface of a neutron star affects the
topology of the magnetic field and how the secular evolution of the binary
system depends on the magnetic field change is still an open issue. We report
evidence for a clear drop in the observed magnetic field in the accreting
pulsar V0332+53 after undergoing a bright 3-month long X-ray outburst. We
determine the field from the position of the fundamental cyclotron line in its
X-ray spectrum and relate it to the luminosity. For equal levels of luminosity,
in the declining phase we measure a systematically lower value of the cyclotron
line energy with respect to the rising phase. This results in a drop of ~1.7 x
10^11 G of the observed field between the onset and the end of the outburst.
The settling of the accreted plasma onto the polar cap seems to induce a
distortion of the magnetic field lines weakening their intensity along the
accretion columns. Therefore the dissipation rate of the magnetic field could
be much faster than previously estimated, unless the field is able to restore
its original configuration on a time-scale comparable with the outbursts
recurrence time. | astro-ph_HE |
ASASSN-18ey: The Rise of a New Black-Hole X-ray Binary: We present the discovery of ASASSN-18ey (MAXI J1820+070), a new black hole
low-mass X-ray binary discovered by the All-Sky Automated Survey for SuperNovae
(ASAS-SN). A week after ASAS-SN discovered ASASSN-18ey as an optical transient,
it was detected as an X-ray transient by MAXI/GCS. Here, we analyze ASAS-SN and
Asteroid Terrestrial-impact Last Alert System (ATLAS) pre-outburst optical
light curves, finding evidence of intrinsic variability for several years prior
to the outburst. While there was no long-term rise leading to outburst, as has
been seen in several other systems, the start of the outburst in the optical
preceded that in the X-rays by $7.20\pm0.97~\rm days$. We analyze the
spectroscopic evolution of ASASSN-18ey from pre-maximum to $> 100~\rm days$
post-maximum. The spectra of ASASSN-18ey exhibit broad, asymmetric,
double-peaked H$\alpha$ emission. The Bowen blend ($\lambda \approx 4650$\AA)
in the post-maximum spectra shows highly variable double-peaked profiles,
likely arising from irradiation of the companion by the accretion disk, typical
of low-mass X-ray binaries. The optical and X-ray luminosities of ASASSN-18ey
are consistent with black hole low-mass X-ray binaries, both in outburst and
quiescence. | astro-ph_HE |
What are Published X-ray lightcurves telling us about Young Supernova
Expansion?: Massive stars lose mass in the form of stellar winds and outbursts. This
material accumulates around the star. When the star explodes as a supernova
(SN) the resulting shock wave expands within this circumstellar medium. The
X-ray emission resulting from the interaction depends, among other parameters,
on the density of this medium, and therefore the variation in the X-ray
luminosity can be used to study the variation in the density structure of the
medium. In this paper we explore the X-ray emission and lightcurves of all
known SNe, in order to study the nature of the medium into which they are
expanding. In particular we wish to investigate whether young SNe are expanding
into a steady wind medium, as is most often assumed in the literature. We find
that in the context of the theoretical arguments that have been generally used
in the literature, many young SNe, and especially those of Type IIn, which are
the brightest X-ray luminosity class, do not appear to be expanding into steady
winds. Some IIns appear to have very steep X-ray luminosity declines,
indicating density declines much steeper than r$^{-2}$. However, other IIns
show a constant or even increasing X-ray luminosity over periods of months to
years. Many other SNe do not appear to have declines consistent with expansion
in a steady wind. SNe with lower X-ray luminosities appear to be more
consistent with steady wind expansion, although the numbers are not large
enough to make firm statistical comments. The numbers do indicate that the
expansion and density structure of the circumstellar medium must be
investigated before assumptions can be made of steady wind expansion. Unless a
steady wind can be shown, mass-loss rates deduced using this assumption may
need to be revised. | astro-ph_HE |
Thick accretion disk and Its super Eddington luminosity around spinning
blackholes: In the general accretion disk model theory, the accretion disk surrounding an
astronomical object comprises fluid rings obeying Keplerian motion. However, we
should consider relativistic and rotational effects as we close in toward the
center of accretion disk surrounding spinning compact massive objects such as a
black hole or a neutron star. In this study, we explore the geometry of the
inner portion of the accretion disk in the context of Mukhopadhyay's pseudo
Newtonian potential approximation for the full general relativity theory. We
found that the shape of the accretion disk "puffs up" or becomes thicker and
the luminosity of the disk could exceed the Eddington luminosity near the
surface of the compact spinning black hole. | astro-ph_HE |
Rapid Generation of Kilonova Light Curves Using Conditional Variational
Autoencoder: The discovery of the optical counterpart, along with the gravitational waves
from GW170817, of the first binary neutron star merger, opened up a new era for
multi-messenger astrophysics. Combining the GW data with the optical
counterpart, also known as AT2017gfo, classified as a kilonova, has revealed
the nature of compact binary merging systems by extracting enriched information
about the total binary mass, the mass ratio, the system geometry, and the
equation of state. Even though the detection of kilonova brought about a
revolution in the domain of multi-messenger astronomy, since there has been
only one kilonova from a gravitational wave detected binary neutron star merger
event so far, this limits the exact understanding of the origin and propagation
of the kilonova. Here, we use a conditional variational autoencoder trained on
light curve data from two kilonova models having different temporal lengths,
and consequently, generate kilonova light curves rapidly based on physical
parameters of our choice with good accuracy. Once trained, the time scale for
light curve generation is of the order of a few milliseconds, thus speeding up
generating light curves by $1000$ times compared to the simulation. The mean
squared error between the generated and original light curves is typically
$0.015$ with a maximum of $0.08$ for each set of considered physical parameter;
while having a maximum of $\approx0.6$ error across the whole parameter space.
Hence, implementing this technique provides fast and reliably accurate results. | astro-ph_HE |
The implications of large binding energies of massive stripped core
collapse supernova progenitors on the explosion mechanism: We examine the binding energies of massive stripped-envelope core collapse
supernova (SECCSN) progenitors with the stellar evolution code MESA, and find
that the jittering jets explosion mechanism is preferred for explosions where
carbon-oxygen cores with masses of $>20 M_\odot$ collapse to leave a neutron
star (NS) remnant. We calculate the binding energy at core collapse under the
assumption that the remnant is a NS. Namely, stellar gas above mass coordinate
of $~1.5-2.5 M_\odot$ is ejected in the explosion. We find that the typical
binding energy of the ejecta of stripped-envelope progenitors with
carbon-oxygen core masses of $M_{CO} > 20 M_\odot$ is $E_{bind}>2 \times
10^{51} erg$. We claim that jets are most likely to explode such cores as
jet-driven explosion mechanisms can supply high energies to the explosion. We
apply our results to SN 2020qlb, which is a SECCSN with a claimed core mass of
$~30-50 M_\odot$, and conclude that the jittering jets explosion mechanism best
accounts for such an explosion that leaves a NS. | astro-ph_HE |
Energy Dependent Time Delays of kHz Oscillations due to Thermal
Comptonization: We study the energy dependent photon variability from a thermal Comptonizing
plasma that is oscillating at kHz frequencies. In particular, we solve the
linearised time dependent Kompaneets equation and consider the oscillatory
perturbation to be either in the soft photon source or in the heating rate of
the plasma. For each case, we self consistently consider the energy balance of
the plasma and the soft photon source. The model incorporates the possibility
of a fraction of the Comptonized photons impinging back into the soft photon
source. We find that when the oscillation is due to the soft photon source, the
variation of the fractional root mean sqaure (r.m.s) is nearly constant with
energy and the time-lags are hard. However, for the case when the oscillation
is due to variation in the heating rate of the corona, and when a significant
fraction of the photons impinge back into the soft photon source, the r.m.s
increases with energy and the time lags are soft. As an example, we compare the
results with the $\sim 850$ Hz oscillation observed on March 3, 1996 for 4U
1608-52 and show that both the observed soft time-lags as well as the r.m.s
versus energy can be well described by such a model where the size of the
Comptonizing plasma is $\sim 1$ km. Thus, modelling of the time lags as due to
Comptonization delays, can provide tight constraints on the size and geometry
of the system. Detailed analysis would require well constrained spectral
parameters. | astro-ph_HE |
How much H and He is "hidden" in SNe Ib/c? -- II. Intermediate-mass
objects: a 22 M$_{\odot}$ progenitor case study: Stripped envelope supernovae are a sub-class of core collapse supernovae
showing several stages of H/He shell stripping that determines the class:
H-free/He-poor SNe are classified as Type Ic, H-poor/He-rich are Type Ib, and
H/He-rich are Type IIb. Stripping H/He with only stellar wind requires
significantly higher mass loss rates than observed while binary-involved mass
transfer may usually not strip enough to produce H/He free SNe. Type Ib/c SNe
are sometimes found to include weak H/He transient lines as a product of a
trace amount of H/He left over from stripping processes. The extent and mass of
the H/He required to produce these lines is not well known. In this work, a 22
M$_{\odot}$ progenitor model is stripped of the H/He shells in five steps prior
to collapse and then exploded at four explosion energies. Requiring both
optical and NIR He I lines for helium identification does not allow much He
mass to be hidden in SE--SNE. Increasing the mass of He above the CO core
delays the visibility of O I 7774 in early spectra. Our SN Ib-like models are
capable of reproducing the spectral evolution of a set of observed SNe with
reasonable estimated $E_\mathrm{k}$ accuracy. Our SN\,IIb-like models can
partially reproduce low energy observed SN IIb, but we find no observed
comparison for the SN IIb-like models with high $E_\mathrm{k}$. | astro-ph_HE |
Magnetic Reconnection in Black-Hole Magnetospheres: Lepton Loading into
Jets, Superluminal Radio Blobs, and Multi-wavelength Flares: Supermassive black holes in active galactic nuclei launch relativistic jets,
as indicated by observed superluminal radio blobs. The energy source of these
jets is widely discussed in the theoretical framework of Blandford-Znajek
process, the electromagnetic energy extraction from rotating black holes (BHs),
while formation mechanism of the radio blobs in the
electromagnetically-dominated jets has been a long-standing problem. Recent
high-resolution magnetohydrodynamic simulations of magnetically arrested disks
exhibited magnetic reconnection in a transient magnetically-dominated part of
the equatorial disk near the BH horizon, which led to a promising scenario of
efficient MeV gamma-ray production and subsequent electron-positron pair
loading into BH magnetosphere. We develop this scenario to build a theoretical
framework on energetics, timescales and particle number density of the
superluminal radio blobs and discuss observable signatures in other wavebands.
We analytically show that the non-thermal electrons emit broadband photons from
optical to multi-MeV bands. The electron-positron pairs produced in the
magnetosphere are optically thick for synchrotron-self absorption, so that the
injected energy is stored in the plasma. The stored energy is enough to power
the superluminal radio blobs observed in M87. This scenario predicts rather dim
radio blobs around Sgr A*, which are consistent with no clear detection by
current facilities. In addition, this scenario inevitably produces strong X-ray
flares in a short timescale, which will be detectable by future X-ray
satellites. | astro-ph_HE |
Mixing of charged and neutral Bose condensates at nonzero temperature
and magnetic field: It is expected that in the interior of compact stars a proton superconductor
coexists with and couples to a neutron superfluid. Starting from a
field-theoretical model for two complex scalar fields - one of which is
electrically charged - we derive a Ginzburg-Landau potential which includes
entrainment between the two fluids and temperature effects from thermal
excitations of the two scalar fields and the gauge field. The Ginzburg-Landau
description is then used for an analysis of the phase structure in the presence
of an external magnetic field. In particular, we study the effect of the
superfluid on the flux tube phase by computing the various critical magnetic
fields and deriving an approximation for the flux tube interaction. As a
result, we point out differences to the naive expectations from an isolated
superconductor, for instance the existence of a first-order flux tube onset,
resulting in a more complicated phase structure in the region between type-I
and type-II superconductivity. | astro-ph_HE |
Comptonization in 1E 1740.7-2942 spectra from 2 to 200 keV: Studies of the long-term spectral variations have been used to constrain the
emission processes of black hole candidates. However, a common scenario which
is able to explain the emission from soft to hard X-rays has been proposed only
recently. Here, we use XMM and INTEGRAL data on 1E 1740.7-2942 in order to
demonstrate that Comptonization plays an important role in producing high
energy photons, as predicted by the current modeling scenario. | astro-ph_HE |
Forbush Decreases during the DeepMin and MiniMax of Solar Cycle 24: After a prolong and deep solar minimum at the end of solar cycle 23, the
current cycle 24 is one of the lowest cycles. The two periods of deep minimum
and mini-maximum of the cycle 24 are connected by a period of increasing solar
activity. In this work, the Forbush decreases of cosmic ray intensity during
the period from January 2008 to December 2014 are studied. A statistical
analysis of 749 events using the IZMIRAN database of Forbush effects obtained
by processing the data of the worldwide neutron monitor network using the
global survey method is performed. A further study of the events that happened
on the Sun and affected the interplanetary space, and finally provoked the
decreases of the galactic cosmic rays near Earth is performed. A statistical
analysis of the amplitude of the cosmic ray decreases with solar and
geomagnetic parameters is carried out. The results will be useful for space
weather studies and especially for Forbush decreases forecasting. | astro-ph_HE |
Astrophysical black holes: In this chapter, we introduce the concept of a black hole (BH) and recount
the initial theoretical predictions. We then review the possible types of BHs
in nature, from primordial, to stellar-mass, to supermassive BHs. Finally, we
focus on the latter category and on their intricate relation with their host
galaxies. | astro-ph_HE |
Evidence for changes in the radiative efficiency of transient black hole
X-ray binaries: We have used pointed RXTE data to examine the long-term X-ray light curves of
six transient black hole X-ray binaries during their decay from outburst to
quiescence. In most cases there is a period of exponential decay as the source
approaches the soft-to-hard state transition, and another period of exponential
decay following this transition as the source decays in the hard state. The
e-folding times change around the time of the state transition, from typically
approx 12 days at the end of the soft state to approx 7 days at the beginning
of the hard state. This factor ~2 change in the decay timescale is expected if
there is a change from radiatively efficient emission in the soft state to
radiatively inefficient emission in the hard state, overlying an exponential
decay in the mass accretion rate. This adds support to the idea that the X-ray
emitting region is governed by radiatively inefficient accretion (such as an
advection-dominated or jet-dominated accretion flow) during the fading hard
state. | astro-ph_HE |
Search for relativistic fractionally charged particles in space: More than a century after the performance of the oil drop experiment, the
possible existence of fractionally charged particles FCP still remains
unsettled. The search for FCPs is crucial for some extensions of the Standard
Model in particle physics. Most of the previously conducted searches for FCPs
in cosmic rays were based on experiments underground or at high altitudes.
However, there have been few searches for FCPs in cosmic rays carried out in
orbit other than AMS-01 flown by a space shuttle and BESS by a balloon at the
top of the atmosphere. In this study, we conduct an FCP search in space based
on on-orbit data obtained using the DArk Matter Particle Explorer (DAMPE)
satellite over a period of five years. Unlike underground experiments, which
require an FCP energy of the order of hundreds of GeV, our FCP search starts at
only a few GeV. An upper limit of $6.2\times 10^{-10}~~\mathrm{cm^{-2}sr^{-1}
s^{-1}}$ is obtained for the flux. Our results demonstrate that DAMPE exhibits
higher sensitivity than experiments of similar types by three orders of
magnitude that more stringently restricts the conditions for the existence of
FCP in primary cosmic rays. | astro-ph_HE |
Gamma-Ray Observations of the Supernova Remnant RX J0852.0-4622 with the
Fermi LAT: We report on gamma-ray observations of the supernova remnant (SNR) RX
J0852.0-4622 with the Large Area Telescope (LAT) aboard the Fermi Gamma-ray
Space Telescope. In the Fermi LAT data, we find a spatially extended source at
the location of the SNR. The extension is consistent with the SNR size seen in
other wavelengths such as X-rays and TeV gamma rays, leading to the
identification of the gamma-ray source with the SNR. The spectrum is well
described as a power law with a photon index of Gamma = 1.85 +/- 0.06 (stat)
(+0.18,-0.19) (sys), which smoothly connects to the H.E.S.S. spectrum in the
TeV energy band. We discuss the gamma-ray emission mechanism based on
multiwavelength data. The broadband data can be fit well by a model in which
the gamma rays are of hadronic origin. We also consider a scenario with inverse
Compton scattering of electrons as the emission mechanism of the gamma rays.
Although the leptonic model predicts a harder spectrum in the Fermi LAT energy
range, the model can fit the data considering the statistical and systematic
errors. | astro-ph_HE |
The Gamma-Ray Burst - Supernova Connection: A preponderance of evidence links long-duration, soft-spectrum gamma-ray
bursts (GRBs) with the death of massive stars. The observations of the
GRB-supernova (SN) connection present the most direct evidence of this physical
link. We summarize 30 GRB-SN associations and focus on five ironclad cases,
highlighting the subsequent insight into the progenitors enabled by detailed
observations. We also address the SN association (or lack thereof) with several
sub-classes of GRBs, finding that the X-ray Flash (XRF) population is likely
associated with massive stellar death whereas short-duration events likely
arise from an older population not readily capable of producing a SN concurrent
with a GRB. Interestingly, a minority population of seemingly long-duration,
soft-spectrum GRBs show no evidence for SN-like activity; this may be a natural
consequence of the range of Ni-56 production expected in stellar deaths. | astro-ph_HE |
The Guided Moments formalism: a new efficient full-neutrino treatment
for astrophysical simulations: We present the new Guided Moments ($\texttt{GM}$) formalism for neutrino
modeling in astrophysical scenarios like core-collapse supernovae and neutron
star mergers. The truncated moments approximation ($\texttt{M1}$) and
Monte-Carlo ($\texttt{MC}$) schemes have been proven to be robust and accurate
in solving the Boltzmann's equation for neutrino transport. However, it is
well-known that each method exhibits specific strengths and weaknesses in
various physical scenarios. The $\texttt{GM}$ formalism effectively solves
these problems, providing a comprehensive scheme capable of accurately
capturing the optically thick limit through the exact $\texttt{M1}$ closure and
the optically thin limit through a $\texttt{MC}$ based approach. In addition,
the $\texttt{GM}$ method also approximates the neutrino distribution function
with a reasonable computational cost, which is crucial for the correct
estimation of the different neutrino-fluid interactions. Our work provides a
comprehensive discussion of the formulation and application of the
$\texttt{GM}$ method, concluding with a thorough comparison across several test
problems involving the three schemes ($\texttt{M1}$, $\texttt{MC}$,
$\texttt{GM}$) under consideration. | astro-ph_HE |
X-ray Measurement of the Spin-Down of Calvera: a Radio- and
Gamma-ray-Quiet Pulsar: We measure spin-down of the 59 ms X-ray pulsar Calvera by comparing the
XMM-Newton discovery data from 2009 with new Chandra timing observations taken
in 2013. Its period derivative is P-dot = (3.19+/-0.08)e-15, which corresponds
to spin-down luminosity E-dot = 6.1e35 erg/s, characteristic age tau_c =
P/2P-dot = 2.9e5 yr, and surface dipole magnetic field strength B_s = 4.4e11 G.
These values rule out a mildly recycled pulsar, but Calvera could be an
orphaned central compact object (anti-magnetar), with a magnetic field that was
initially buried by supernova debris and is now reemerging and approaching
normal strength. We also performed unsuccessful searches for high-energy
gamma-rays from Calvera in both imaging and timing of >100 MeV Fermi photons.
Even though the distance to Calvera is uncertain by an order of magnitude, an
upper limit of d < 2 kpc inferred from X-ray spectra implies a gamma-ray
luminosity limit of < 3.3e32 erg/s, which is less than that of any pulsar of
comparable E-dot. Calvera shares some properties with PSR J1740+1000, a young
radio pulsar that we show by virtue of its lack of proper motion was born
outside of the Galactic disk. As an energetic, high-Galactic-latitude pulsar,
Calvera is unique in being undetected in both radio and gamma-rays to faint
limits, which should place interesting constraints on models for particle
acceleration and beam patterns in pulsar magnetospheres. | astro-ph_HE |
On the Rate of Neutron Star Binary Mergers from Globular Clusters: The first detection of gravitational waves from a neutron star - neutron star
(NS-NS) merger, GW170817, and the increasing number of observations of short
gamma-ray bursts (SGRBs) have greatly motivated studies of the origins of NS-NS
and neutron star - black hole (NS-BH) binaries. We calculate the merger rates
of NS-NS and NS-BH binaries from globular clusters (GCs) using realistic GC
simulations with the \texttt{CMC} cluster catalog. We use a large sample of
models with a range of initial numbers of stars, metallicities, virial radii
and galactocentric distances, representative of the present-day Milky Way GCs,
to quantify the inspiral times and volumetric merger rates as a function of
redshift, both inside and ejected from clusters. We find that over the complete
lifetime of most GCs, stellar BHs dominate the cluster cores and prevent the
mass segregation of NSs, thereby reducing the dynamical interaction rates of
NSs so that at most a few NS binary mergers are ever produced. We estimate the
merger rate in the local universe to be $\sim\rm{0.02\,Gpc^{-3}\,yr^{-1}}$ for
both NS-NS and NS-BH binaries, or a total of $\sim 0.04$~Gpc$^{-3}$~yr$^{-1}$
for both populations. These rates are about 5 orders of magnitude below the
current empirical merger rate from LIGO/Virgo. We conclude that dynamical
interactions in GCs do not play a significant role in enhancing the NS-NS and
NS-BH merger rates. | astro-ph_HE |
Precursors of Short Gamma-Ray Bursts in the SPI-ACS/INTEGRAL Experiment: We have analyzed the light curves of 519 short gamma-ray bursts (GRBs)
detected in the SPI-ACS/INTEGRAL experiment from December 2002 to May 2014 to
search for precursors. Both the light curves of 519 individual events and the
averaged light curve of 372 brightest bursts have been analyzed. In a few
cases, we have found and thoroughly studied precursor candidates based on
SPI-ACS/INTEGRAL, GBM/Fermi, and LAT/Fermi data. A statistical analysis of the
averaged light curve for the entire sample of short bursts has revealed no
regular precursor. Upper limits for the relative intensity of precursors have
been estimated. No convincing evidence for the existence of precursors of short
GRBs has been found. We show that the fraction of short GRBs with precursors is
less than 0.4% of all short bursts. | astro-ph_HE |
High-energy gamma-ray observations of Geminga with the Fermi Large Area
Telescope: Geminga is the second brightest persistent source in the GeV gamma-ray sky.
Discovered in 1975 by SAS-2 mission, it was identified as a pulsar only in the
90s, when ROSAT detected the 237 ms X-ray periodicity, that was later also
found by EGRET in gamma rays. Even though Geminga has been one of the most
intensively studied isolated neutron star during the last 30 years, its
interest remains intact especially at gamma-ray energies, where instruments
like the Large Area Telescope (LAT) aboard the Fermi mission will provide an
unprecedented view of this pulsars. We will report on the preliminary results
obtained on the analysis of the first year of observations. We have been able
to do precise timing of Geminga using solely gamma rays, producing a timing
solution and allowing a deep study of the evolution of the light curve with
energy. We have also measured and studied the high-energy cutoff in the
phase-averaged spectrum and produced a detailed study of the spectral evolution
with phase. | astro-ph_HE |
Nonthermal X-ray Emission from the N11 Superbubble in the Large
Magellanic Cloud: We present the results of X-ray spectral analysis of the superbubble around
the OB association LH9 in the H II complex N11 in the Large Magellanic Cloud.
Using observations from Suzaku, we have modeled the X-ray emission over the
energy range 0.2-7.5 keV. We constrained the thermal spectrum below 2 keV using
a thermal plasma model found in a previous XMM-Newton study of the N11 region.
We find that the hard X-ray emission (> 2 keV) requires a nonthermal power-law
component. The photon index of this component was found to be $\Gamma=1.72\pm
0.15$. We performed an energy budget analysis for N11 using the known stellar
content of LH9. We found that the observed thermal and kinetic energy in the
superbubble is only half of the expected mechanical energy injected by stars. | astro-ph_HE |
On the physical meaning of the 2.1 keV absorption feature in 4U 1538-52: The improvement of the capabilities of nowadays X-ray observatories, like
Chandra or XMM-Newton, offers the possibility to detect both absorption and
emission lines and to study the nature of the matter surrounding the neutron
star in X-ray binaries and the phenomena that produce these lines. The aim of
this work is to discuss the different physical scenarios in order to explain
the meaning of the significant absorption feature present in the X-ray spectrum
of 4U 1538-52. Using the last available calibrations, we discard the
possibility that this feature is due to calibration, gain effects or be
produced by the X-ray background or a dust region. Giving the energy resolution
of the XMM-Newton telescope we could not establish if the line is formed in the
atmosphere of the neutron star or by the dispersion of the stellar wind of the
optical counterpart. | astro-ph_HE |
Simple waves in relativistic fluids: We consider the Riemann problem for relativistic flows of polytropic fluids
and find relations for the flow characteristics. Evolution of physical
quantities take especially simple form for the case of cold magnetized plasmas.
We find exact, explicit analytical solutions for one dimensional expansion of
magnetized plasma into vacuum, valid for arbitrary magnetization. We also
consider expansion into cold unmagnetized external medium both for stationary
initial conditions and for initially moving plasma, as well as reflection of
rarefaction wave from a wall. We also find self-similar structure of
three-dimensional magnetized outflows into vacuum, valid close to the
plasma-vacuum interface.
The key results of this work, the self-similar solutions, were incorporated
post-initial submission into appendices of the published version of Granot et
al. (2010). | astro-ph_HE |
Expansion and Age of the Supernova Remnant G350.1-0.3: High-Velocity
Iron Ejecta from a Core-Collapse Event: We report Chandra observations of the highly asymmetric core-collapse
supernova remnant G350.1-0.3. We document expansion over 9 years away from the
roughly stationary central compact object, with sky-plane velocities up to
$5000 d_{4.5}$ km s$^{-1}$ ($d_{4.5}$ is the distance in units of 4.5 kpc),
redshifts ranging from 900 km s$^{-1}$ to 2600 km s$^{-1}$, and
three-dimensional space velocities approaching 6000 km s$^{-1}$. Most of the
bright emission comes from heavy-element ejecta particularly strong in iron.
Iron-enhanced ejecta are seen at 4000 - 6000 km s$^{-1}$, strongly suggesting
that the supernova was not a common Type IIP event. While some fainter regions
have roughly solar abundances, we cannot identify clear blast-wave features.
Our expansion proper motions indicate that G350.1-0.3 is no more than about 600
years old, independent of distance: the third youngest known core-collapse
supernova in the Galaxy, and one of the most asymmetric. | astro-ph_HE |
Multiple Peaks and a Long Precursor in the Type IIn Supernova 2021qqp:
An Energetic Explosion in a Complex Circumsteller Environment: We present detailed optical photometry and spectroscopy of the Type IIn
supernova (SN) 2021qqp. Its unusual light curve is marked by a long gradual
brightening (i.e., precursor) for about 300 days, a rapid increase in
brightness for about 60 days, and then a sharp increase of about 1.6 mag in
only a few days to a first peak of $M_r\approx -19.5$ mag. The light curve then
turns over and declines rapidly, until it re-brightens to a second distinct and
sharp peak with $M_r\approx -17.3$ mag centered at about 335 days after the
first peak. The spectra are dominated by Balmer-series lines with a complex
morphology that includes a narrow component with a width of $\approx 1300$ km
s$^{-1}$ (first peak) and $\approx 2500$ km s$^{-1}$ (second peak) that we
associate with the circumstellar medium (CSM), and a P Cygni component with an
absorption velocity of $\approx 8500$ km s$^{-1}$ (first peak) and $\approx
5600$ km s$^{-1}$ (second peak) that we associate with the SN-CSM interaction
shell. Using the bolometric light curve and velocity evolution, we construct an
analytical model to extract the CSM profile and SN properties. We find two
significant mass-loss episodes with peak mass loss rates of $\approx 10$
M$_\odot$ yr$^{-1}$ and $\approx 5$ M$_\odot$ yr$^{-1}$ about 0.8 and 2 years
before explosion, and a total CSM mass of $\approx 2-4\,M_\odot$. We show that
the most recent mass-loss episode can explain the precursor for the year
preceding the explosion. The SN ejecta mass is constrained to be $M_{\rm
SN}\approx 5-30\,M_\odot$ for an explosion energy of $E_{\rm SN}\approx
(3-10)\times10^{51}\,{\rm erg}$. We discuss eruptive massive stars (luminous
blue variable, pulsational pair instability) and an extreme stellar merger with
a compact object as possible progenitor channels for generating the energetic
explosion in the complex CSM environment. | astro-ph_HE |
Disentangling multiple high-energy emission components in the Vela X
pulsar wind nebula with the Fermi Large Area Telescope: Vela X is a pulsar wind nebula in which two relativistic particle populations
with distinct spatial and spectral distributions dominate the emission at
different wavelengths. An extended $2^\circ \times 3^\circ$ nebula is seen in
radio and GeV gamma rays. An elongated cocoon prevails in X-rays and TeV gamma
rays. We use 9.5 years of data from the Fermi Large Area Telescope (LAT) to
disentangle gamma-ray emission from the two components in the energy range from
10 GeV to 2 TeV, bridging the gap between previous measurements at GeV and TeV
energies. We determine the morphology of emission associated to Vela X
separately at energies < 100 GeV and > 100 GeV, and compare it to the
morphology seen at other wavelengths. Then, we derive the spectral energy
distribution of the two gamma-ray components over the full energy range. The
best fit to the LAT data is provided by the combination of the two components
derived at energies < 100 GeV and > 100 GeV. The first component has a soft
spectrum, spectral index $2.19\pm0.16^{+0.05}_{-0.22}$, and extends over a
region of radius $1.36^\circ\pm0.04^\circ$, consistent with the radio nebula.
The second component has a harder spectrum, spectral index
$0.9\pm0.3^{+0.3}_{-0.1}$, and is concentrated over an area of radius
$0.63^\circ\pm0.03^\circ$, coincident with the X-ray cocoon that had already
been established to account for the bulk of the emission at TeV energies. The
spectrum measured for the low-energy component corroborates previous evidence
for a roll-over of the electron spectrum at energies of a few tens of GeV
possibly due to diffusive escape. The high-energy component has a very hard
spectrum: if the emission is produced by electrons with a power-law spectrum
the electrons must be uncooled, and there is a hint that their spectrum may be
harder than predictions by standard models of Fermi acceleration at
relativistic shocks. (Abridged) | astro-ph_HE |
Radio-Frequency Searches for Dark Matter in Dwarf Galaxies: Dwarf spheroidal galaxies have long been discussed as optimal targets for
indirect dark matter searches. However, the majority of such studies have been
conducted with gamma-ray instruments. In this review, we discuss the very
recent progress that has been made in radio-based indirect dark matter
searches. We look at existing work on this topic and discuss the future
prospects that motivate continued work in this newly developing field that
promises to become, in the light of the up-coming Square Kilometre Array, a
prominent component of the hunt for dark matter. | astro-ph_HE |
Ultra-high energy cosmic ray correlations with Active Galactic Nuclei in
the world dataset: Pierre Auger collaboration have recently put forward the hypothesis that the
arrival directions of the highest energy cosmic rays correlate with the subset
of local active galactic nuclei (AGN). We perform a blind test of AGN
hypothesis using publicly available event sets collected by Yakutsk, AGASA and
HiRes experiments. The consistency of the procedure requires the event energies
to be normalized towards the common energy scale. The number of correlating
events in resulting data-set is 3 of 21 which is consistent with expected
random background. | astro-ph_HE |
Cosmic ray streaming in the turbulent interstellar medium: We study the streaming instability of GeV$-100~$GeV cosmic rays (CRs) and its
damping in the turbulent interstellar medium (ISM). We find that the damping of
streaming instability is dominated by ion-neutral collisional damping in weakly
ionized molecular clouds, turbulent damping in the highly ionized warm medium,
and nonlinear Landau damping in the Galactic halo. Only in the Galactic halo,
is the streaming speed of CRs close to the Alfv\'{e}n speed. Alfv\'{e}nic
turbulence plays an important role in both suppressing the streaming
instability and regulating the diffusion of streaming CRs via magnetic field
line tangling, with the effective mean free path of streaming CRs in the
observer frame determined by the Alfv\'{e}nic scale in super-Alfv\'{e}nic
turbulence. The resulting diffusion coefficient is sensitive to Alfv\'{e}n Mach
number, which has a large range of values in the multi-phase ISM.
Super-Alfv\'{e}nic turbulence contributes to additional confinement of
streaming CRs, irrespective of the dominant damping mechanism. | astro-ph_HE |
Modeling High-energy and Very-high-energy gamma-rays from the Terzan 5
Cluster: The Fermi Large Area Telescope (LAT) has recently detected a population of
globular clusters (GCs) in high-energy (HE) gamma-rays. Their spectral
properties and energetics are consistent with cumulative emission from a
population of millisecond pulsars (MSPs) hosted by these clusters. For example,
the HE spectra exhibit fairly hard power-law indices and cutoffs around a few
GeV, typical of pulsed spectra measured for the gamma-ray pulsar population.
The energetics may be used to constrain the number of visible MSPs in the
cluster (N_vis), assuming canonical values for the average gamma-ray efficiency
and spin-down power. This interpretation is indeed strengthened by the fact
that the first gamma-ray MSP has now been identified in the GC NGC 6624, and
this MSP is responsible for almost all of the HE emission from this cluster. On
the other hand, it has been argued that the MSPs are also sources of
relativistic leptons which may be reaccelerated in shocks originating in
collisions of stellar winds in the cluster core, and may upscatter bright
starlight and cosmic microwave background photons to very high energies.
Therefore, this unpulsed component may give an independent constraint on the
total number of MSPs (N_tot) hosted in the GC, for a given cluster magnetic
field B and diffusion coefficient k_0. Lastly, the transport properties of the
energetic leptons may be further constrained using multiwavelength data, e.g.,
to infer the radial dependence of k_0 and B. We present results on our modeling
of the pulsed and unpulsed gamma-ray fluxes from the GC Terzan 5. | astro-ph_HE |
MeV Pulsars: Modeling Spectra and Polarization: A sub-population of energetic rotation-powered pulsars show high fluxes of
pulsed non-thermal hard X-ray emission. While this MeV pulsar population
includes some radio-loud pulsars like the Crab, a significant number have no
detected radio or GeV emission, a mystery since gamma- ray emission is a common
characteristic of pulsars with high spin-down power. Their steeply rising hard
X-ray spectral energy distributions (SEDs) suggest peaks at 0.1 - 1 MeV but
they have not been detected above 200 keV. Several upcoming and planned
telescopes may shed light on the MeV pulsars. The Neutron star Interior
Composition ExploreR (NICER) will observe pulsars in the 0.2 - 12 keV band and
may discover additional MeV pulsars. Planned telescopes, such as All-Sky
Medium-Energy Gamma-Ray Observatory (AMEGO) and e-ASTROGAM, will detect
emission above 0.2 MeV and polarization in the 0.2 - 10 MeV band. We present a
model for the spectrum and polarization of MeV pulsars where the X-ray emission
comes from electron- positron pairs radiating in the outer magnetosphere and
current sheet. This model predicts that the peak of the SED increases with
surface magnetic field strength if the pairs are produced in polar cap
cascades. For small inclination angles, a range of viewing angles can miss both
the radio pulse and the GeV pulse from particles accelerating near the current
sheet. Characterizing the emission and geometry of MeV pulsars can thus provide
clues to the source of pairs and acceleration in the magnetosphere. | astro-ph_HE |
A re-analysis of the NuSTAR and XMM-Newton broad-band spectrum of
Ser~X-1: Context: Ser X-1 is a well studied LMXB which clearly shows a broad iron
line. Recently, Miller et al. (2103) have presented broad-band, high quality
NuSTAR data of SerX-1.Using relativistically smeared self-consistent reflection
models, they find a value of R_in close to 1.0 R_ISCO (corresponding to 6 R_g),
and a low inclination angle, less than 10 deg. Aims: The aim of this paper is
to probe to what extent the choice of reflection and continuum models (and
uncertainties therein) can affect the conclusions about the disk parameters
inferred from the reflection component. To this aim we re-analyze all the
available public NuSTAR and XMM-Newton. Ser X-1 is a well studied source, its
spectrum has been observed by several instruments, and is therefore one of the
best sources for this study. Methods: We use slightly different continuum and
reflection models with respect to those adopted in literature for this source.
In particular we fit the iron line and other reflection features with
self-consistent reflection models as reflionx (with a power-law illuminating
continuum modified with a high energy cutoff to mimic the shape of the incident
Comptonization spectrum) and rfxconv. With these models we fit NuSTAR and
XMM-Newton spectra yielding consistent spectral results. Results: Our results
are in line with those already found by Miller et al. (2013) but less extreme.
In particular, we find the inner disk radius at about 13 R_g and an inclination
angle with respect to the line of sight of about 27 deg. We conclude that,
while the choice of the reflection model has little impact on the disk
parameters, as soon as a self-consistent model is used, the choice of the
continuum model can be important in the precise determination of the disk
parameters from the reflection component. Hence broad-band X-ray spectra are
highly preferable to constrain the continuum and disk parameters. | astro-ph_HE |
Embedded Spiral Patterns in the Cool Core of the Massive Cluster of
Galaxies Abell 1835: We present the properties of intracluster medium (ICM) in the cool core of
the massive cluster of galaxies Abell 1835 obtained with the data by $ Chandra$
$X$-$ray$ $Observatory$. We find distinctive spiral patterns with the radius of
70 kpc (or 18 arcsec) as a whole in the residual image of X-ray surface
brightness after the 2-dimensional ellipse model of surface brightness is
subtracted. The size is smaller by a factor of 2 -- 4 than that of other
clusters known to have a similar pattern. The spiral patterns consist of two
arms. One of them appears as positive, and the other does as negative excesses
in the residual image. Their X-ray spectra show that the ICM temperatures in
the positive- and negative-excess regions are $5.09^{+0.12}_{-0.13}$ keV and
$6.52^{+0.18}_{-0.15}$ keV, respectively. In contrast, no significant
difference is found in the abundance or pressure, the latter of which suggests
that the ICM in the two regions of the spiral patterns is in pressure
equilibrium or close. The spatially-resolved X-ray spectroscopy of the central
region ($r<40$ arcsec) divided into 92 sub-regions indicates that Abell 1835 is
a typical cool core cluster. We also find that the spiral patterns extend from
the cool core out to the hotter surrounding ICM. The residual image reveals
some lumpy sub-structure in the cool core. The line-of-sight component of the
disturbance velocity responsible for the sub-structures is estimated to be
lower than 600 km/s. Abell 1835 may be now experiencing an off-axis minor
merger. | astro-ph_HE |
Resolving the puzzle of type IIP SN 2016X: The enigmatic type IIP SN 2016X demonstrates the unprecedented asphericity in
the nebular H-alpha line profile, the absence of nebular [O I] emission, and
the unusual occultation effect due to the internal dust. The hydrodynamic
modelling of the bolometric light curve and expansion velocities suggests that
the event is an outcome of the massive star explosion that ejected 28 Msun with
the kinetic energy of 1.7x10^51 erg and 0.03 Msun of radioactive Ni-56. We
recover the bipolar distribution of Ni-56 from the H-alpha profile via the
simulation of the emissivity produced by non-spherical Ni-56 ejecta. The
conspicuous effect of the dust absorption in the H-alpha profile rules out the
occultation by the dusty sphere or dusty thick disk but turns out consistent
with the thin dusty disk-like structure in the plane perpendicular to the
bipolar axis. We speculate that the absence of the nebular [O I] emission might
originate from the significant cooling of the oxygen-rich matter mediated by CO
and SiO molecules. | astro-ph_HE |
Simulation study on origin of multi-core events in cosmic rays extensive
air showers: Some experiments have found multi-core events in cosmic rays extensive air
showers which should be interpreted by hadronic interaction theory. In this
paper, the multi-core events are reproduced by Monte Carlo simulation with
CORSIKA. The origin of each sub-cores is tracked back from the observation
level. The interaction mechanism and original particles of sub-core are studied
in this paper. | astro-ph_HE |
A Proper Motion for the Pulsar Wind Nebula G359.23-0.82, "the Mouse,"
Associated with the Energetic Radio Pulsar J1747-2958: The "Mouse" (PWN G359.23-0.82) is a spectacular bow shock pulsar wind nebula,
powered by the radio pulsar J1747-2958. The pulsar and its nebula are presumed
to have a high space velocity, but their proper motions have not been directly
measured. Here we present 8.5 GHz interferometric observations of the Mouse
nebula with the Very Large Array, spanning a time baseline of 12 yr. We measure
eastward proper motion for PWN G359.23-0.82 (and hence indirectly for PSR
J1747-2958) of 12.9+/-1.8 mas/yr, which at an assumed distance of 5 kpc
corresponds to a transverse space velocity of 306+/-43 km/s. Considering
pressure balance at the apex of the bow shock, we calculate an in situ hydrogen
number density of approximately 1.0(-0.2)(+0.4) cm^(-3) for the interstellar
medium through which the system is traveling. A lower age limit for PSR
J1747-2958 of 163(-20)(+28) kyr is calculated by considering its potential
birth site. The large discrepancy with the pulsar's spin-down age of 25 kyr is
possibly explained by surface dipole magnetic field growth on a timescale ~15
kyr, suggesting possible future evolution of PSR J1747-2958 to a different
class of neutron star. We also argue that the adjacent supernova remnant
G359.1-0.5 is not physically associated with the Mouse system but is rather an
unrelated object along the line of sight. | astro-ph_HE |
Time Evolution of Pulsar Magnetosphere I - An Implicit Approach: We apply a computationally efficient technique to validate the global
structure of the pulsar magnetosphere. In this first of a series of studies, a
3D, computationally intensive, implicit Crank-Nicolson finite-difference scheme
is developed. The region of magnetic influence is evolved under the
approximation of force-free electrodynamics. The main objective of this paper
is to present our code and use it to demonstrate and verify the now widely -
accepted global features of a pulsar magnetosphere. Our results qualitatively
agree with previously developed time-dependent models for an oblique rotator.
In line with earlier studies, we also demonstrate that our simulations can run
for many stellar rotations. Once we extend our code, we believe that our
implicit approach can be extremely useful to investigate magnetospheres filled
with resistive plasma, develop better resolution current sheets and investigate
small scale microphysics of pair creation using particle-in-cell techniques. | astro-ph_HE |
Assessing luminosity correlations via cluster analysis: Evidence for
dual tracks in the radio/X-ray domain of black hole X-ray binaries: [abridged] The radio:X-ray correlation for hard and quiescent state black
hole X-ray binaries is critically investigated in this paper. New observations
of known sources, along with newly discovered ones, have resulted in an
increasingly large number of outliers lying well outside the scatter about the
quoted best-fit relation. Here, we employ and compare state of the art data
clustering techniques in order to identify and characterize different data
groupings within the radio:X-ray luminosity plane for 18 hard and quiescent
state black hole X-ray binaries with nearly simultaneous multi-wavelength
coverage. Linear regression is then carried out on the clustered data to infer
the parameters of a relationship of the form {ell}_{r}=alpha+beta {ell}_x
through a Bayesian approach (where {ell} denotes log lum). We conclude that the
two cluster model, with independent linear fits, is a significant improvement
over fitting all points as a single cluster. While the upper track slope
(0.63\pm0.03) is consistent, within the errors, with the fitted slope for the
2003 relation (0.7\pm0.1), the lower track slope (0.98\pm0.08) is not
consistent with the upper track, nor it is with the widely adopted value of
~1.4 for the neutron stars. The two luminosity tracks do not reflect systematic
differences in black hole spins as estimated either from reflection, or
continuum fitting method. These results are insensitive to the selection of
sub-samples, accuracy in the distances, and to the treatment of upper limits.
Besides introducing a further level of complexity in understanding the
interplay between synchrotron and Comptonised emission from black hole X-ray
binaries, the existence of two tracks in the radio:X-ray domain underscores
that a high level of caution must be exercised when employing black hole
luminosity relations for the purpose of estimating a third parameter, such as
distance or mass. | astro-ph_HE |
Soft gamma-ray constraints on a bright flare from the Galactic Center
supermassive black hole: Sagittarius A* (Sgr A*) is the supermassive black hole residing at the center
of the Milky Way. It has been the main target of an extensive multiwavelength
campaign we carried out in April 2007. Herein, we report the detection of a
bright flare from the vicinity of the horizon, observed simultaneously in
X-rays (XMM/EPIC) and near infrared (VLT/NACO) on April 4th for 1-2 h. For the
first time, such an event also benefitted from a soft gamma-rays
(INTEGRAL/ISGRI) and mid infrared (VLT/VISIR) coverage, which enabled us to
derive upper limits at both ends of the flare spectral energy distribution
(SED). We discuss the physical implications of the contemporaneous light curves
as well as the SED, in terms of synchrotron, synchrotron self-Compton and
external Compton emission processes. | astro-ph_HE |
Tidal Instability and Superhump by a Wave-Wave Resonant Model: On a disk deformed to a non-axisymmetric form, a set of oscillations can be
excited by their resonant interaction through the disk deformation (Kato et al.
2011). This resonant instability process has been proposed to suggest a
possible cause of the high-frequency quasi-periodic oscillations (HF QPOs)
observed in black-hole low-mass X-ray binaries. In the present paper, we
examine whether the above-mentioned wave-wave resonant process can describe the
tidal instability and superhump in dwarf novae. The results show that the
process seems to well describe the observations. If this process is really the
cause of the tidal instability and superhump, a two-armed oscillation with high
frequency roughly on the magnitude of three times the orbital frequency is
present on disks, although its expected amplitude may be small. | astro-ph_HE |
Constraints on the source of ultra-high energy cosmic rays using
anisotropy vs chemical composition: The joint analysis of anisotropy signals and chemical composition of
ultra-high energy cosmic rays offers strong potential for shedding light on the
sources of these particles. Following up on an earlier idea, this paper studies
the anisotropies produced by protons of energy >E/Z, assuming that anisotropies
at energy >E have been produced by nuclei of charge Z, which share the same
magnetic rigidity. We calculate the number of secondary protons produced
through photodisintegration of the primary heavy nuclei. Making the extreme
assumption that the source does not inject any proton, we find that the
source(s) responsible for anisotropies such as reported by the Pierre Auger
Observatory should lie closer than ~20-30, 80-100 and 180-200 Mpc if the
anisotropy signal is mainly composed of oxygen, silicon and iron nuclei
respectively. A violation of this constraint would otherwise result in the
secondary protons forming a more significant anisotropy signal at lower
energies. Even if the source were located closer than this distance, it would
require an extraordinary metallicity >120, 1600, 1100 times solar metallicity
in the acceleration zone of the source, for oxygen, silicon and iron
respectively, to ensure that the concomitantly injected protons not to produce
a more significant low energy anisotropy. This offers interesting prospects for
constraining the nature and the source of ultra-high energy cosmic rays with
the increase in statistics expected from next generation detectors. | astro-ph_HE |
Fragmentation cross-sections and model uncertainties in Cosmic Ray
propagation physics: Abundances and energy spectra of cosmic ray nuclei are being measured with
high accuracy by the AMS experiment. These observations can provide tight
constraints to the propagation models of galactic cosmic rays. In the view of
the release of these data, I present an evaluation of the model uncertainties
associated to the cross-sections for secondary production of Li-Be-B nuclei in
cosmic rays. I discuss the role of cross section uncertainties in the
calculation of the boron-to-carbon and beryllium-to-boron ratios, as well as
their impact in the determination of the cosmic-ray transport parameters. | astro-ph_HE |
Diffuse flux of PeV neutrinos from centrifugally accelerated protons in
active galactic nuclei: Evidence for high-energy astrophysical PeV neutrinos has been found in the
IceCube experiment from an analysis with a 7.5 year (2010 - 2017) data. Active
galactic nuclei (AGN) are among the most prominent objects in the universe, and
are widely speculated to be emitters of ultra-high-energy (UHE) cosmic rays
with proton domination. Based on the standard two-step LLCD mechanism of
particle acceleration, a transformation of energy occurs from AGN's central
super-massive black hole (SMBH) rotation to high-energy protons. Protons can be
accelerated up to $\sim 0.1$ EeV energies and above, and might generate PeV
neutrinos in the energy range $1$--$10$~ PeV through plausible hadronic
interactions. The theoretically estimated revised extragalactic diffuse muon
neutrino flux employing the "luminosity-dependent density evolution (LDDE)"
model for the AGN luminosity function (LF) is found consistent with the IceCube
level if only a fraction, $6.56\%$ of the total bolometric luminosity (BL) of
AGN is being realizable to power the PeV neutrinos. In the $\Lambda$~CDM
cosmological framework with the LDDE modeled LF and photon index distribution,
about $5.18\%$ of the total BL is enough to power the IceCube neutrinos. | astro-ph_HE |
Newtonian analogue of corresponding spacetime dynamics of rotating black
holes: Implication on black hole accretion: Based on the conserved Hamiltonian for a test particle, we have formulated a
Newtonian analogue of Kerr spacetime in the `low energy limit of the test
particle motion' that, in principle, can be comprehensively used to describe
general relativistic (GR) features of Kerr spacetime, however, with less
accuracy for high spin. The derived potential, which has an explicit velocity
dependence, contains the entire relativistic features of corresponding
spacetime including the frame dragging effect, unlike other prevailing
pseudo-Newtonian potentials (PNPs) for the Kerr metric where such an effect is
either totally missing or introduced in a ad hoc manner. The particle dynamics
with this potential precisely reproduce the GR results within a maximum ~ 10 %
deviation in energy for a particle orbiting circularly in the vicinity of a
rapidly corotating black hole. GR epicyclic frequencies are also well
reproduced with the potential, though with a relatively higher percentage of
deviation. For counterrotating cases, the obtained potential replicate the GR
results with precise accuracy. The Kerr-Newtonian potential also approximates
the radius of marginally stable and marginally bound circular orbits with
reasonable accuracy for a < 0.7. Importantly, the derived potential can imitate
the experimentally tested GR effects like perihelion advancement and bending of
light with reasonable accuracy. The formulated Kerr-Newtonian potential thus
can be useful to study complex accreting plasma dynamics and its implications
around rotating BHs in the Newtonian framework, avoiding GR gas dynamical
equations. | astro-ph_HE |
Potential Gamma-ray Emissions from Low-Mass X-ray Binary Jets: By proposing a pure leptonic radiation model, we study the potential
gamma-ray emissions from jets of the low-mass X-ray binaries. In this model,
the relativistic electrons that are accelerated in the jets are responsible for
radiative outputs. Nevertheless, dynamics of jets are dominated by the magnetic
and proton-matter kinetic energies. The model involves all kinds of related
radiative processes and considers the evolution of relativistic electrons along
the jet by numerically solving the kinetic equation. Numerical results show
that the spectral energy distributions can extend up to TeV bands, in which
synchrotron radiation and synchrotron self-Compton scattering are dominant
components. As an example, we apply the model to the low-mass X-ray binary GX
339-4. The results can not only reproduce the currently available observations
from GX 339-4, but also predict detectable radiation at GeV and TeV bands by
Fermi and CTA telescopes. The future observations with Fermi and CTA can be
used to test our model, which could be employed to distinguish the origin of
X-ray emissions. | astro-ph_HE |
Kinetic modeling of the electromagnetic precursor from an axisymmetric
binary pulsar coalescence: The recent detection of gravitational waves associated with a binary neutron
star merger revives interest in interacting pulsar magnetospheres. Current
models predict that a significant amount of magnetic energy should be released
prior to the merger, leading to electromagnetic precursor emission. In this
paper, we revisit this problem in the light of the recent progress in kinetic
modeling of pulsar magnetospheres. We limit our work to the case of aligned
magnetic moments and rotation axes, and thus neglect the orbital motion. We
perform global two-dimensional axisymmetric particle-in-cell simulations of two
pulsar magnetospheres merging at a rate consistent with the emission of
gravitational waves. Both symmetric and asymmetric systems are investigated.
Simulations show a significant enhancement of magnetic dissipation within the
magnetospheres as both stars get closer. Even though the magnetospheric
configuration depends on the relative orientations of the pulsar spins and
magnetic axes, all configurations present nearly the same radiative signature,
indicating that a common dissipation mechanism is at work. The relative motion
of both pulsars drives magnetic reconnection at the boundary between the two
magnetospheres, leading to efficient particle acceleration and high-energy
synchrotron emission. Polar-cap discharge is also strongly enhanced in
asymmetric configurations, resulting in vigorous pair production and
potentially additional high-energy radiation. We observe an increase in the
pulsar radiative efficiency by two orders of magnitude over the last orbit
before the merger exceeding the spindown power of an isolated pulsar. The
expected signal is too weak to be detected at high energies even in the nearby
universe. However, if a small fraction of this energy is channeled into radio
waves, it could be observed as a non-repeating fast radio burst. | astro-ph_HE |
The proton-air inelastic cross-section measurement at $\sqrt{s} \approx
$ 2 TeV from EAS-TOP experiment: The proton-air inelastic cross section value \sigmapairin=338$\pm$21({\it
stat})$\pm$19({\it syst})-28({\it syst}) mb at $\sqrt{s} \approx $ 2 TeV has
been measured by the EAS-TOP Extensive Air Shower experiment. The absorption
length of cosmic ray proton primaries cascades reaching the maximum development
at the observation level is obtained from the flux attenuation for different
zenith angles (i.e. atmospheric depths). The analysis, including the effects of
the heavier primaries contribution and systematic uncertainties, is described.
The experimental result is compared with different high energy interaction
models and the relationships with the {\it pp} ($\bar pp$) total cross section
measurements are discussed. | astro-ph_HE |
Low X-ray emission challenges supernovae remnants as the source of
cosmic-ray electrons: The X-ray synchrotron emission of each of the young supernova-remnants (SNRs)
SN1006, Kepler, Tycho, RCW86 and Cas A, is roughly given by $\nu L_{\nu}\sim
10^{45}\rm{erg}/t$, where $t$ is the remnant's age. The electrons emitting the
X-ray emission cool fast, implying that the X-ray emission is calorimetric and
equal to half of the cosmic ray (CR) electron acceleration efficiency (per
logarithmic interval of particle energies, at multi TeV energies). Assuming
Sedov-Taylor expansion, the resulting CR electron yield per SNR is estimated to
be $E^2dN_e/dE\approx 6\nu L_{\nu}t \sim 10^{46}\rm erg$. This is about two
orders of magnitudes below the required amount for explaining the observed
electron CRs at $E\sim 10\rm GeV$. Possible resolutions are 1. a soft
acceleration spectrum allowing much more energy at $E\sim 10\rm GeV$ compared
to $E\sim 10\rm TeV$, 2. an increased acceleration efficiency at later phases
of the SNR evolution (unlikely), or 3. SNRs are not the source of CR electrons. | astro-ph_HE |
Coherent Network Analysis of Gravitational Waves from Three-Dimensional
Core-Collapse Supernova Models: Using predictions from three-dimensional (3D) hydrodynamics simulations of
core-collapse supernovae (CCSNe), we present a coherent network analysis to
detection, reconstruction, and the source localization of the
gravitational-wave (GW) signals. We use the {\tt RIDGE} pipeline for the
analysis, in which the network of LIGO Hanford, LIGO Livingston, VIRGO, and
KAGRA is considered. By combining with a GW spectrogram analysis, we show that
several important hydrodynamics features in the original waveforms persist in
the waveforms of the reconstructed signals. The characteristic excess in the
spectrograms originates not only from rotating core-collapse, bounce and the
subsequent ring down of the proto-neutron star (PNS) as previously identified,
but also from the formation of magnetohydrodynamics jets and non-axisymmetric
instabilities in the vicinity of the PNS. Regarding the GW signals emitted near
at the rotating core bounce, the horizon distance extends up to $\sim$ 18 kpc
for the most rapidly rotating 3D model in this work. Following the rotating
core bounce, the dominant source of the GW emission shifts to the
non-axisymmetric instabilities. The horizon distances extend maximally up to
$\sim$ 40 kpc seen from the spin axis. With an increasing number of 3D models
trending towards explosion recently, our results suggest that in addition to
the best studied GW signals due to rotating core-collapse and bounce, the time
is ripe to consider how we can do science from GWs of CCSNe much more seriously
than before. Particularly the quasi-periodic signals due to the
non-axisymmetric instabilities and the detectability should deserve further
investigation to elucidate the inner-working of the rapidly rotating CCSNe. | astro-ph_HE |
Why Haven't Many of the Brightest Radio Loud Blazars Been Detected by
Fermi ?: We use the complete MOJAVE 1.5 Jy sample of active galactic nuclei (AGN) to
examine the gamma-ray detection statistics of the brightest radio-loud blazars
in the northern sky. We find that 23% of these AGN were not detected above 0.1
GeV by the Fermi LAT during the 4-year 3FGL catalog period partly because of an
instrumental selection effect, and partly due to their lower Doppler boosting
factors. Blazars with synchrotron peaks in their spectral energy distributions
located below $10^{13.4}$ Hz also tend to have high-energy peaks that lie below
the 0.1 GeV threshold of the LAT, and are thus less likely to be detected by
Fermi. The non-detected AGN in the 1.5 Jy sample also have significantly lower
15 GHz radio modulation indices and apparent jet speeds, indicating that they
have lower than average Doppler factors. Since the effective amount of
relativistic Doppler boosting is enhanced in gamma-rays (particularly in the
case of external inverse-Compton scattering), this makes them less likely to
appear in the 3FGL catalog. Based on their observed properties, we have
identified several bright radio-selected blazars that are strong candidates for
future detection by Fermi. | astro-ph_HE |
Optical Observations of the Type Ia Supernova 2011fe in M101 for Nearly
500 Days: We present well-sampled optical observations of the bright Type Ia supernova
(SN~Ia) SN 2011fe in M101. Our data, starting from $\sim16$ days before maximum
light and extending to $\sim463$ days after maximum, provide an unprecedented
time series of spectra and photometry for a normal SN~Ia. Fitting the
early-time rising light curve, we find that the luminosity evolution of SN
2011fe follows a $t^n$ law, with the index $n$ being close to 2.0 in the $VRI$
bands but slightly larger in the $U$ and $B$ bands. Combining the published
ultraviolet (UV) and near-infrared (NIR) photometry, we derive the contribution
of UV/NIR emission relative to the optical. SN 2011fe is found to have stronger
UV emission and reaches its UV peak a few days earlier than other SNe~Ia with
similar $\Delta m_{15}(B)$, suggestive of less trapping of high-energy photons
in the ejecta. Moreover, the $U$-band light curve shows a notably faster
decline at late phases ($t\approx 100$--300 days), which also suggests that the
ejecta may be relatively transparent to UV photons. These results favor the
notion that SN 2011fe might have a progenitor system with relatively lower
metallicity. On the other hand, the early-phase spectra exhibit prominent
high-velocity features (HVFs) of O~I $\lambda$7773 and the Ca~II~NIR triplet,
but only barely detectable in Si~II~6355. This difference can be caused either
by an ionization/temperature effect or an abundance enhancement scenario for
the formation of HVFs; it suggests that the photospheric temperature of SN
2011fe is intrinsically low, perhaps owing to incomplete burning during the
explosion of the white dwarf. | astro-ph_HE |
Metallicity Effect on LMXB Formation in Globular Clusters: We present comprehensive observational results of the metallicity effect on
the fraction of globular clusters (GC) that contain low-mass X-ray binaries
(LMXB), by utilizing all available data obtained with Chandra for LMXBs and HST
ACS for GCs. Our primary sample consists of old elliptical galaxies selected
from the ACS Virgo and Fornax surveys. To improve statistics at both the lowest
and highest X-ray luminosity, we also use previously reported results from
other galaxies. It is well known that the LMXB fraction is considerably higher
in red, metal-rich, than in blue, metal-poor GCs. In this paper, we test
whether this metallicity effect is X-ray luminosity-dependent, and find that
the effect holds uniformly in a wide luminosity range. This result is
statistically significant (at >= 3 sigma) in LMXBs with luminosities in the
range LX = 2 x 10^37 - 5 x 10^38 erg s-1, where the ratio of LMXB fractions in
metal-rich to metal-poor GCs is R = 3.4 +- 0.5. A similar ratio is also found
at lower (down to 10^36 erg s-1) and higher luminosities (up to the ULX
regime), but with less significance (~2 sigma confidence). Because different
types of LMXBs dominate in different luminosities, our finding requires a new
explanation for the metallicity effect in dynamically formed LMXBs. We confirm
that the metallicity effect is not affected by other factors such as stellar
age, GC mass, stellar encounter rate, and galacto-centric distance. | astro-ph_HE |
Precision ephemerides for gravitational-wave searches -- III. Revised
system parameters of Sco X-1: Neutron stars in low-mass X-ray binaries are considered promising candidate
sources of continuous gravitational-waves. These neutron stars are typically
rotating many hundreds of times a second. The process of accretion can
potentially generate and support non-axisymmetric distortions to the compact
object, resulting in persistent emission of gravitational-waves. We present a
study of existing optical spectroscopic data for Sco X-1, a prime target for
continuous gravitational-wave searches, with the aim of providing revised
constraints on key orbital parameters required for a directed search with
advanced-LIGO data. From a circular orbit fit to an improved radial velocity
curve of the Bowen emission components, we derived an updated orbital period
and ephemeris. Centre of symmetry measurements from the Bowen Doppler tomogram
yield a centre of the disc component of 90 km $\mathrm{s^{-1}}$, which we
interpret as a revised upper limit to the projected orbital velocity of the NS
$K_1$. By implementing Monte Carlo binary parameter calculations, and imposing
new limits on $K_1$ and the rotational broadening, we obtained a complete set
of dynamical system parameter constraints including a new range for $K_1$ of
40--90 km $\mathrm{s^{-1}}$. Finally, we discussed the implications of the
updated orbital parameters for future continuous-waves searches. | astro-ph_HE |
Charged current neutrino interactions in core-collapse supernovae in a
virial expansion: Core-collapse supernovae may depend sensitively on charged current neutrino
interactions in warm, low density neutron rich matter. A proton in neutron rich
matter is more tightly bound than is a neutron. This energy shift \Delta U
increases the electron energy in \nu_e + n --> p + e, increasing the available
phase space and absorption cross section. Likewise \Delta U decreases the
positron energy in \bar \nu_e + p --> n + e^+, decreasing the phase space and
cross section. We have calculated \Delta U using a model independent virial
expansion and we find \Delta U is much larger, at low densities, than the
predictions of many mean field models. Therefore \Delta U could have a
significant impact on charged current neutrino interactions in supernovae.
Preliminary simulations of the accretion phase of core-collapse supernovae find
that \Delta U increases \bar \nu_e energies and decreases the \nu_e luminosity. | astro-ph_HE |
Search for anisotropic Lorentz invariance violation with γ-rays: While Lorentz invariance, the fundamental symmetry of Einstein's theory of
General Relativity, has been tested to a great level of detail, Grand Unified
Theories that combine gravity with the other three fundamental forces may
result in a violation of Lorentz symmetry at the Planck scale. These energies
are unattainable experimentally. However, minute deviations from Lorentz
invariance may still be present at much lower energies. These deviations can
accumulate over large distances, making astrophysical measurements the most
sensitive tests of Lorentz symmetry. One effect of Lorentz invariance violation
is an energy dependent photon dispersion of the vacuum resulting in differences
of the light travel time from distant objects. The Standard-Model Extension
(SME) is an effective theory to describe the low-energy behavior of a more
fundamental Grand Unified Theory, including Lorentz and CPT violating terms. In
the SME the Lorentz violating operators can in part be classified by their
mass-dimension d, with the lowest order being d=5. However, measurements of
photon polarization have constrained operators with d=5 setting lower limits on
the energy at which they become dominant well beyond the Planck scale. On the
other hand, these operators also violate CPT, and thus d=6 could be the leading
order. In this paper we present constraints on all 25 real coefficients
describing anisotropic non-birefringent Lorentz invariance violation at mass
dimension d=6 in the SME. We used Fermi-LAT observations of 25 active galactic
nuclei to constrain photon dispersion and combined our results with previously
published limits in order to simultaneously constrain all 25 coefficients. This
represents the first set of constraints on these coefficients of a
mass-dimension d=6, whereas previous measurements were only able to constrain
linear combinations of all 25 coefficients. | astro-ph_HE |
Detecting Stellar Lensing of Gravitational Waves with Ground-Based
Observatories: We investigate the ability of ground based gravitational wave observatories
to detect gravitational wave lensing events caused by stellar mass lenses. We
show that LIGO and Virgo possess the sensitivities required to detect lenses
with masses as small as $\sim 30 M_\odot$ provided that the gravitational wave
is observed with a signal-to-noise ratio of $\sim30$. Third generation
observatories will allow detection of gravitational wave lenses with masses of
$\sim 1 M_\odot$. Finally, we discuss the possibility of lensing by multiple
stars, as is the case if the gravitational radiation is passing through
galactic nucleus or a dense star cluster. | astro-ph_HE |
Effects of Compton Cooling on outflows in a Two Component Accretion Flow
around a Black Hole: Results of a Coupled Monte Carlo-TVD Simulation: The effect of cooling on the outflow rate from an accretion disk around a
black hole is investigated using a coupled Monte Carlo Total Variation
Diminishing code. A correlation between the spectral states and the outflow
rates is found as a consequence. | astro-ph_HE |
The Definitive X-ray Light Curve of Swift J164449.3+573451: On March 28, 2011, the Swift Burst Alert Telescope triggered on an object
that had no analog in over six years of Swift operations. Follow-up
observations by the Swift X-ray Telescope (XRT) found a new, bright X-ray
source covering 3 orders of magnitude in flux over the first few days, that was
much more persistent (and variable) than gamma-ray burst afterglows.
Ground-based spectroscopy found a redshift of 0.35, implying extremely high
luminosity, with integrated isotropic-equivalent energy output in the X-ray
band alone exceeding $10^{53}$ ergs in the first two weeks after discovery.
Strong evidence for a collimated outflow or beamed emission was found. The
observational properties of this object are unlike anything ever before
observed. We interpret these unique properties as the result of emission from a
relativistic jet produced in the aftermath of the tidal disruption of a main
sequence star by a massive black hole (BH) in the center of the host galaxy.
The source decayed slowly as the stellar remnants were accreted onto the BH,
before abruptly shutting off. Here we present the definitive XRT team light
curve for Swift J164449.3+573451 and discuss its implications. We show that the
unabsorbed flux decayed roughly as a $t^{-1.5}$ power law up to August 17,
2012. The steep turnoff of an order of magnitude in 24 hours seems to be
consistent with the shutdown of the jet as the accretion disk transitioned from
a thick disk to a thin disk. Swift continues to monitor this source in case the
jet reactivates. | astro-ph_HE |
An extended Heitler-Matthews model for the full hadronic cascade in
cosmic air showers: The Heitler-Matthews model for hadronic air showers will be extended to all
the generations of electromagnetic subshowers in the hadronic cascade. The
analysis is outlined in detail for showers initiated by primary protons. For
showers initiated by iron primaries the part of the analysis is given for as
far as it differs from the analysis for a primary proton. Predictions for
shower sizes and the depth of maximum shower size are compared with results of
Monte Carlo simulations. The depth of maximum as it follows from the
extrapolation of the Heitler-Matthews model restricted to the first generation
of electromagnetic subshowers is too small with respect to Monte Carlo
predictions. It is shown that the inclusion of all the generations of
electromagnetic subshowers leads to smaller predictions for the depth of
maximum and to smaller predictions for the elongation rate. The discrepancy
between discrete model predictions and Monte Carlo predictions for the depth of
maximum can therefore not be explained from the number of generations that is
taken into consideration. An alternative explanation will be proposed. | astro-ph_HE |
Search for gamma-ray emission from four accreting millisecond pulsars
with Fermi/LAT: We report our search for \gamma-ray emission in the energy range from 100 MeV
to 300 GeV from four Accreting Millisecond Pulsars (AMPs), SAX J1808.4-3658,
IGR J00291+5934, XTE J1814-338, and XTE J0929-314. The data are from four-year
observations carried out by Large Area Telescope (LAT) onboard the Fermi
\gamma-ray Space Telescope. The AMPs were not detected, and their \gamma-ray
luminosity upper limits we obtain are 5.1*10^33 ergs/s for SAX J1808.4-3658,
2.1*10^33 ergs/s for IGR J00291+5934, 1.2*10^34 ergs/s for XTE J1814-338, and
2.2*10^33 ergs/s for XTE J0929-314. We compare our results with \gamma-ray
irradiation luminosities required for producing optical modulations seen from
the companions in the AMPs, which has been suggested by Takata et al. (2012),
and our upper limits have excluded \gamma-ray emission as the heating source in
these systems except XTE J0929-314, the upper limit of which is not deep
enough. Our results also do not support the model proposed by Takata et al.
(2012) that relatively strong \gamma-ray emission could arise from the outer
gap of a high-mass neutron star controlled by the photon-photon pair-creation
for the AMPs. Two AMPs, SAX J1808.4-3658 and IGR J00291+5934, have the
measurements of their spin-down rates, and we derive the upper limits of their
\gamma-ray conversion efficiencies, which are 57% and 3%, respectively. We
discuss the implications to the AMP systems by comparing the efficiency upper
limit values with that of 20 \gamma-ray millisecond pulsars (MSP) detected by
Fermi and the newly discovered transitional MSP binary J1023+0038. | astro-ph_HE |
Gamma-Ray Observational Properties of TeV-Detected Blazars: The synergy between the Fermi-LAT and ground-based Cherenkov telescope arrays
gives us the opportunity for the first time to characterize the high-energy
emission from blazars over 5 decades in energy, from 100 MeV to 10 TeV. In this
study, we perform a Fermi-LAT spectral analysis for TeV-detected blazars and
combine it with archival TeV data. We examine the observational properties in
the gamma-ray band of our sample of TeV-detected blazars and compare the
results with X-ray and GeV-selected populations. The spectral energy
distributions (SEDs) that result from combining Fermi-LAT and ground-based
spectra are studied in detail. Simple parameterizations such as a power-law
function do not always reproduce the high-energy SEDs, where spectral features
that could indicate intrinsic absorption are observed. | astro-ph_HE |
GRB 091208B: First Detection of the Optical Polarization in Early
Forward Shock Emission of a Gamma-Ray Burst Afterglow: We report that the optical polarization in the afterglow of GRB 091208B is
measured at t = 149 - 706 s after the burst trigger, and the polarization
degree is P = 10.4% +/- 2.5%. The optical light curve at this time shows a
power-law decay with index -0.75 +/- 0.02, which is interpreted as the forward
shock synchrotron emission, and thus this is the first detection of the
early-time optical polarization in the forward shock (rather than that in the
reverse shock reported by Steele et al. (2009). This detection disfavors the
afterglow model in which the magnetic fields in the emission region are random
on the plasma skin depth scales, such as amplified by the plasma instabilities,
e.g., Weibel instability. We suggest that the fields are amplified by the
magnetohydrodynamic instabilities, which would be tested by future observations
of the temporal changes of the polarization degrees and angles for other
bursts. | astro-ph_HE |
The high-energy emission of millisecond pulsars: This chapter provides a phenomenological appraisal of the high-energy
emission of millisecond pulsars. We comment on some of their properties as a
population, as well as consider the especial cases of transitional pulsars,
other redbacks, and black widow systems. | astro-ph_HE |
Constraints on the optical precursor to the naked-eye burst GRB080319B
from Pi of the Sky observations: I present the results of the search for an optical precursor to the naked-eye
burst - GRB080319B, which reached 5.87m optical peak luminosity in the "Pi of
the Sky" data. A burst of such a high brightness could have been preceded by an
optical precursor luminous enough to be in detection range of our experiment.
The "Pi of the Sky" cameras observed the coordinates of the GRB for about 20
minutes prior to the explosion, thus provided crucial data for the precursor
search. No signal within 3 sigma limit was found. A limit of 12m (V-band
equivalent) was set based on the data combined from two cameras, the most
robust limit to my knowledge for this precursor. | astro-ph_HE |
X-ray Polarimetry of the accreting pulsar 1A~0535+262 in the
supercritical state with PolarLight: The X-ray pulsar 1A 0535+262 exhibited a giant outburst in 2020, offering us
a unique opportunity for X-ray polarimetry of an accreting pulsar in the
supercritical state. Measurement with PolarLight yielded a non-detection in 3-8
keV; the 99% upper limit of the polarization fraction (PF) is found to be 0.34
averaged over spin phases, or 0.51 based on the rotating vector model. No
useful constraint can be placed with phase resolved polarimetry. These upper
limits are lower than a previous theoretical prediction of 0.6-0.8, but
consistent with those found in other accreting pulsars, like Her X-1, Cen X-3,
4U 1626-67, and GRO J1008-57, which were in the subcritical state, or at least
not confidently in the supercritical state, during the polarization
measurements. Our results suggest that the relatively low PF seen in accreting
pulsars cannot be attributed to the source not being in the supercritical
state, but could be a general feature. | astro-ph_HE |
{\it Suzaku} observation of Galactic supernova remnant CTB 37A
(G348.5+0.1): We present here the results of the observation of CTB 37A obtained with the
X-ray Imaging Spectrometer onboard the {\it Suzaku} satellite. The X-ray
spectrum of CTB 37A is well fitted by two components, a single-temperature
ionization equilibrium component (VMEKAL) with solar abundances, an electron
temperature of $kT_{\rm e}\sim0.6$ keV, absorbing column density of $N_{\rm
H}\sim3\times10^{22}$ ${\rm cm^{-2}}$ and a power-law component with photon
index of $\Gamma$ $\sim 1.6$. The X-ray spectrum of CTB 37A is characterized by
clearly detected K-shell emission lines of Mg, Si, S, and Ar. The plasma with
solar abundances supports the idea that the X-ray emission originates from the
shocked interstellar material. The ambient gas density, and age of the remnant
are estimated to be $\sim1f^{-1/2}$${\rm cm^{-3}}$ and
$\sim3\times10^{4}f^{1/2}$ yr, respectively. The center-filling X-ray emission
surrounded by a shell-like radio structure and other X-ray properties indicate
that this remnant would be a new member of mixed-morphology supernova remnant
class. | astro-ph_HE |
A flaring magnetar in FRB 121102?: The persistent radio counterpart of FRB 121102 is estimated to have $N\sim
10^{52}$ particles, energy $E_N\sim 10^{48}$ erg, and size $R\sim 10^{17}$ cm.
The source can be a nebula inflated and heated by an intermittent outflow from
a magnetar --- a neutron star powered by its magnetic (rather than rotational)
energy. The object is young and frequently liberating energy in magnetic flares
driven by accelerated ambipolar diffusion in the neutron star core, feeding the
nebula and producing bright millisecond bursts. The particle number in the
nebula is consistent with ion ejecta from giant flares. The nebula may also
contain the freeze-out of electron-positron pairs $N_\pm\sim 10^{51}$ created
months after the neutron star birth; the same mechanism offers an explanation
for $N_\pm$ in the Crab nebula. The persistent source around FRB 121102 is
likely heated by magnetic dissipation and internal waves excited by the
magnetar ejecta. The volumetric heating by waves explains the nebula's enormous
efficiency in producing radio emission. The repeating radio bursts are
suggested to occur much closer to the magnetar, whose flaring magnetosphere
drives ultrarelativistic internal shocks into the magnetar wind. The shocks are
mediated by Larmor rotation that forms a GHz maser with the observed ms
duration. Furthermore, the flare ejecta can become charge-starved and then
convert to electromagnetic waves. | astro-ph_HE |
$JetCurry$ I. Reconstructing Three-Dimensional Jet Geometry from
Two-Dimensional Images: We present a three-dimensional (3-D) visualization of jet geometry using
numerical methods based on a Markov Chain Monte Carlo (MCMC) and limited memory
Broyden-Fletcher-Goldfarb-Shanno (BFGS) optimized algorithm. Our aim is to
visualize the 3-D geometry of an active galactic nucleus (AGN) jet using
observations, which are inherently two-dimensional (2-D) images. Many AGN jets
display complex structures that include hotspots and bends. The structure of
these bends in the jet's frame may appear quite different than what we see in
the sky frame, where it is transformed by our particular viewing geometry. The
knowledge of the intrinsic structure will be helpful in understanding the
appearance of the magnetic field and hence emission and particle acceleration
processes over the length of the jet. We present the $JetCurry$ algorithm to
visualize the jet's 3-D geometry from its 2-D image. We discuss the underlying
geometrical framework and outline the method used to decompose the 2-D image.
We report the results of our 3-D visualization of the jet of M87, using the
test case of the knot D region. Our 3-D visualization is broadly consistent
with the expected double helical magnetic field structure of the knot D region
of the jet. We also discuss the next steps in the development of the $JetCurry$
algorithm. | astro-ph_HE |
Quark matter with strong magnetic field and possibility of the third
family of compact stars: We consider the possibility for the existence of the third family of compact
objects, considering the effect of strong magnetic fields inside the hybrid
stars. As a result, we demonstrate such new sequences of stable equilibrium
configurations for some hadronic equations of state. Through the analysis of
the adiabatic index inside stars, we find the conditions for appearing the
third family of compact objects, i.e., for hadronic stars without quarks, that
the maximum mass should be small, the central density for the maximum mass
should be also small, and the radius for the the maximum mass should be large.
Even for soft hadronic equations of state, the two solar-mass stars might
survive as the third family of compact objects, once quark matter with strong
magnetic field, such as $\sim {\cal O}(10^{19} {\rm G})$, is taken into
account. It might give a hint to solve the so-called hyperon puzzle in nuclear
physics. | astro-ph_HE |
Low-frequency gravitational wave memory from gamma-ray burst afterglows
with energy injection: Ultrarelativistic gamma-ray burst (GRB) jets are strong gravitational wave
(GW) sources with memory-type signals. The plateau (or shallow decay) phases
driven by the energy injection might appear in the early X-ray afterglows of
GRBs. In this paper, we investigate the GW signal as well as X-ray afterglow
emission in the framework of GRB jets with energy injection, and both short-
and long-duration GRBs are considered. We find that, regardless of the case,
because of the antibeaming and time delay effects, a rising slope emerging in
the waveform of GW signal due to the energy injection lags far behind the
energy ejection, and the typical frequency of the characteristic amplitudes
falls within a low-frequency region of $\sim10^{-4}-10^{-6} \,{\rm Hz}$; and we
consider that the GW memory triggered by GRB jets with energy injection are
previously unaware and the nearby GRBs with strong energy injection might
disturb the measurement of the stochastic GW background. Such GW memory
detection would provide a direct test for models of energy injection in the
scenario of GRB jets. | astro-ph_HE |
Multifrequency studies of the narrow-line Seyfert 1 galaxy SBS 0846+513: The narrow-line Seyfert 1 galaxy SBS 0846+513 was first detected by the Large
Area Telescope (LAT) on-board Fermi in 2011 June-July when it underwent a
period of flaring activity. Since then, as Fermi continues to accumulate data
on this source, its flux has been monitored on a daily basis. Two further
gamma-ray flaring episodes from SBS 0846+513 were observed in 2012 May and
August, reaching a daily peak flux integrated above 100 MeV of (50+/-12)x10^-8
ph/cm^2/s, and (73+/-14)x10^-8 ph/cm^2/s on May 24 and August 7, respectively.
Three outbursts were detected at 15 GHz by the Owens Valley Radio Observatory
40-m telescope in 2012 May, 2012 October, and 2013 January, suggesting a
complex connection with the gamma-ray activity. The most likely scenario
suggests that the 2012 May gamma-ray flare may not be directly related to the
radio activity observed over the same period, while the two gamma-ray flaring
episodes may be related to the radio activity observed at 15 GHz in 2012
October and 2013 January. The gamma-ray flare in 2012 May triggered Swift
observations that confirmed that SBS 0846+513 was also exhibiting high activity
in the optical, UV and X-ray bands, thus providing a firm identification
between the gamma-ray source and the lower-energy counterpart. We compared the
spectral energy distribution (SED) of the flaring state in 2012 May with that
of a quiescent state. The two SEDs, modelled as an external Compton component
of seed photons from a dust torus, could be fitted by changing the electron
distribution parameters as well as the magnetic field. No significant evidence
of thermal emission from the accretion disc has been observed. Interestingly,
in the 5 GHz radio luminosity vs. synchrotron peak frequency plot SBS 0846+513
seems to lie in the flat spectrum radio quasar part of the so-called `blazar
sequence'. | astro-ph_HE |
Modeling the Spectrum of IGR J17177-3656: The correlation between radio and X-ray luminosity in the hard state of black
hole X-ray binaries is important for unveiling the relation between the
accretion flow and the jets. In this paper, we have modeled the
quasi-simultaneous multi-band observations of a recently discovered transient
X-ray source, IGR J17177-3656. It is found that the source is probably an
outlier following the steep radio/X-ray correlation rather than an outlier in
the transition region as suggested by Paizis et al. (2011). It is also found
that the multi-band spectrum can be successfully modeled by the luminous hot
accretion flow (LHAF) but less likely by the advection dominated accretion flow
(ADAF). Our results support the point that LHAF can explain the steep
radio/X-ray correlation. | astro-ph_HE |
Observational Signatures of Black Hole Accretion: Rotating vs. Spherical
Flows with Tilted Magnetic Fields: We study the observational signatures of magnetically arrested black hole
accretion with non-rotating inflow onto a rotating black hole; we consider a
range of angles between the black hole spin and the initial magnetic field
orientation. We compare the results of our General Relativistic
Magneto-Hydrodynamic simulations to more commonly used rotating initial
conditions and to the Event Horizon Telescope (EHT) observations of M87. We
find that the mm intensity images, polarization images, and synchrotron
emission spectra are very similar among the different simulations when
post-processed with the same electron temperature model; observational
differences due to different electron temperature models are significantly
larger than those due to the different realizations of magnetically arrested
accretion. The orientation of the mm synchrotron polarization is particularly
insensitive to the initial magnetic field orientation, the electron temperature
model, and the rotation of the inflowing plasma. The largest difference among
the simulations with different initial rotation and magnetic tilt is in the
strength and stability of the jet; spherical inflow leads to kink-unstable
jets. We discuss the implications of our results for current and future EHT
observations and for theoretical models of event-horizon-scale black hole
accretion. | astro-ph_HE |
The short bursts in SGR 1806-20, 1E 1048-5937 and SGR 0501+4516: We analyzed temporal and spectral properties, focusing on the short bursts,
for three anomalous X-ray pulsars (AXPs) and soft gamma repeaters (SGRs),
including SGR 1806-20, 1E 1048-5937 and SGR 0501+4516. Using the data from
XMM-Newton, we located the short bursts by Bayesian blocks algorithm. The short
bursts' duration distributions for three sources were fitted by two lognormal
functions. The spectra of shorter bursts ($< 0.2~\rm s$) and longer bursts
($\geq 0.2~\rm s$) can be well fitted in two blackbody components model or
optically thin thermal bremsstrahlung model for SGR 0501+4516. We also found
that there is a positive correlation between the burst luminosity and the
persistent luminosity with a power law index $\gamma = 1.23 \pm 0.18 $. The
energy ratio of this persistent emission to the time averaged short bursts is
in the range of $10 - 10^3$, being comparable to the case in Type I X-ray
burst. | astro-ph_HE |
Disentangling the Origin and Heating Mechanism of Supernova Dust:
Late-Time Spitzer Spectroscopy of the Type IIn SN 2005ip: This paper presents late-time near-infrared and {\it Spitzer} mid-infrared
photometric and spectroscopic observations of warm dust in the Type IIn SN
2005ip in NGC 2906. The spectra show evidence for two dust components with
different temperatures. Spanning the peak of the thermal emission, these
observations provide strong constraints on the dust mass, temperature, and
luminosity, which serve as critical diagnostics for disentangling the origin
and heating mechanism of each component. The results suggest the warmer dust
has a mass of $\sim 5 \times 10^{-4}~$\msolar, originates from newly formed
dust in the ejecta, or possibly the cool, dense shell, and is continuously
heated by the circumstellar interaction. By contrast, the cooler component
likely originates from a circumstellar shock echo that forms from the heating
of a large, pre-existing dust shell $\sim 0.01 - 0.05$~\msolar~by the late-time
circumstellar interaction. The progenitor wind velocity derived from the blue
edge of the He 1 1.083 \micron~P Cygni profile indicates a progenitor eruption
likely formed this dust shell $\sim$100 years prior to the supernova explosion,
which is consistent with a Luminous Blue Variable (LBV) progenitor star. | astro-ph_HE |
Multi-messenger and real-time astrophysics with the Baikal-GVD telescope: The Baikal-GVD deep underwater neutrino experiment participates in the
international multi-messenger program on discovering the astrophysical sources
of high energy fluxes of cosmic particles, while being at the stage of
deployment with a gradual increase of its effective volume to the scale of a
cubic kilometer. In April 2021 the effective volume of the detector has been
reached 0.4 km3 for cascade events with energy above 100 TeV generated by
neutrino interactions in Lake Baikal. The alarm system in real-time monitoring
of the celestial sphere was launched at the beginning of 2021, that allows to
form the alerts of two ranks like "muon neutrino" and "VHE cascade". Recent
results of fast follow-up searches for coincidences of Baikal-GVD high energy
cascades with ANTARES/TAToO high energy neutrino alerts and IceCube GCN
messages will be presented, as well as preliminary results of searches for high
energy neutrinos in coincidence with the magnetar SGR 1935+2154 activity in
period of radio and gamma burst in 2020. | astro-ph_HE |
Geodesic models of quasi-periodic-oscillations as probes of quadratic
gravity: Future very-large-area X-ray instruments (for which the effective area is
larger than $>3$m$^2$) will be able to measure the frequencies of
quasi-periodic oscillations~(QPOs) observed in the X-ray flux from accreting
compact objects with sub-percent precision. If correctly modeled, QPOs can
provide a novel way to test the strong-field regime of gravity. By using the
relativistic precession model and a modified version of the epicyclic resonance
model, we develop a method to test general relativity against a generic class
of theories with quadratic curvature corrections. With the instrumentation
being studied for future missions such as eXTP, LOFT, or STROBE-X, a
measurement of at least two QPO triplets from a stellar mass black hole can set
stringent constraints on the coupling parameters of quadratic gravity. | astro-ph_HE |
The GALEX Time Domain Survey. II. Wavelength-Dependent Variability of
Active Galactic Nuclei in the Pan-STARRS1 Medium Deep Survey: We analyze the wavelength-dependent variability of a sample of
spectroscopically confirmed active galactic nuclei (AGN) selected from near-UV
($NUV$) variable sources in the GALEX Time Domain Survey that have a large
amplitude of optical variability (difference-flux S/N $>$ 3) in the Pan-STARRS1
Medium Deep Survey (PS1 MDS). By matching GALEX and PS1 epochs in 5 bands
($NUV$, $g_{P1}$, $r_{P1}$, $i_{P1}$, $z_{P1}$) in time, and taking their flux
difference, we create co-temporal difference-flux spectral energy distributions
($\Delta f$SEDs) using two chosen epochs for each of the 23 objects in our
sample on timescales of about a year.
We confirm the "bluer-when-brighter" trend reported in previous studies, and
measure a median spectral index of the $\Delta f$SEDs of $\alpha_{\lambda}$ =
2.1 that is consistent with an accretion disk spectrum. We further fit the
$\Delta f$SEDs of each source with a standard accretion disk model in which the
accretion rate changes from one epoch to the other. In our sample, 17 out of 23
($\sim$74 %) sources are well described by this variable accretion-rate disk
model, with a median average characteristic disk temperature $\bar{T}^*$ of
$1.2\times 10^5$~K that is consistent with the temperatures expected given the
distribution of accretion rates and black hole masses inferred for the sample.
Our analysis also shows that the variable accretion rate model is a better fit
to the $\Delta f$SEDs than a simple power law. | astro-ph_HE |
Probing AGN variability with the Cherenkov Telescope Array: Relativistic jets launched by Active Galactic Nuclei are among the most
powerful particle accelerators in the Universe. The emission over the entire
electromagnetic spectrum of these relativistic jets can be extremely variable
with scales of variability from less than few minutes up to several years.
These variability patterns, which can be very complex, contain information
about the acceleration processes of the particles and the area(s) of emission.
Thanks to its sensitivity, five-to twenty-times better than the current
generation of Imaging Atmospheric Cherenkov Telescopes depending on energy, the
Cherenkov Telescope Array will be able to follow the emission from these
objects with a very accurate time sampling and over a wide spectral coverage
from 20 GeV to > 20 TeV and thus reveal the nature of the acceleration
processes at work in these objects. We will show the first results of our
lightcurve simulations and long-term behavior of AGN as will be observed by
CTA, based on state-of-art particle acceleration models. | astro-ph_HE |
Influence of a Galactic Gamma-Ray Burst on Ocean Plankton: The hypothesis that one or more biodiversity drops in the Phanerozoic eon,
evident in the geological record, might have been caused by the most powerful
kind of stellar explosion so far known Gamma Ray Bursts (GRB) has been
discussed in several works. These stellar explosions could have left an imprint
in the biological evolution on Earth and in other habitable planets. In this
work we calculate the short-term lethality that a GRB would produce in the
aquatic primary producers on Earth. This effect on life appears because of
ultraviolet (UV) retransmission in the atmosphere of a fraction of the gamma
energy, resulting in an intense UV flash capable of penetrating tens of meters
in the water column in the ocean. We focus on the action of the UV flash on
phytoplankton, as they are the main contributors to global aquatic primary
productivity. Our results suggest that the UV flash could cause a significant
reduction of phytoplankton biomass in the upper mixed layer of the World Ocean. | astro-ph_HE |
First search for atmospheric and extraterrestrial neutrino-induced
cascades with the IceCube detector: We report on the first search for atmospheric and for diffuse astrophysical
neutrino-induced showers (cascades) in the IceCube detector using 257 days of
data collected in the year 2007-2008 with 22 strings active. A total of 14
events with energies above 16 TeV remained after event selections in the
diffuse analysis, with an expected total background contribution of $8.3\pm
3.6$. At 90% confidence we set an upper limit of
$E^2\Phi_{90%CL}<3.6\times10^{-7} GeV \cdot cm^{-2} \cdot s^{-1}\cdot sr^{-1} $
on the diffuse flux of neutrinos of all flavors in the energy range between 24
TeV and 6.6 PeV assuming that $\Phi \propto E^{-2}$ and that the flavor
composition of the $\nu_e : \nu_\mu : \nu_\tau$ flux is $1 : 1 : 1$ at the
Earth. The atmospheric neutrino analysis was optimized for lower energies. A
total of 12 events were observed with energies above 5 TeV. The observed number
of events is consistent with the expected background, within the uncertainties. | astro-ph_HE |
Magnetically-driven crustquakes in neutron stars: Crustquake events may be connected with both rapid spin-up `glitches' within
the regular slowdown of neutron stars, and high-energy magnetar flares. We
argue that magnetic field decay builds up stresses in a neutron star's crust,
as the elastic shear force resists the Lorentz force's desire to rearrange the
global magnetic-field equilibrium. We derive a criterion for crust-breaking
induced by a changing magnetic-field configuration, and use this to investigate
strain patterns in a neutron star's crust for a variety of different
magnetic-field models. Universally, we find that the crust is most liable to
break if the magnetic field has a strong toroidal component, in which case the
epicentre of the crustquake is around the equator. We calculate the energy
released in a crustquake as a function of the fracture depth, finding that it
is independent of field strength. Crust-breaking is, however, associated with a
characteristic local field strength of $2.4\times 10^{14}$ G for a breaking
strain of $0.001$, or $2.4\times 10^{15}$ G at a breaking strain of $0.1$. We
find that even the most luminous magnetar giant flare could have been powered
by crustal energy release alone. | astro-ph_HE |
Understanding the Unusual X-Ray Emission Properties of the Massive,
Close Binary WR 20a: A High Energy Window into the Stellar Wind Initiation
Region: The problem of explaining the X-ray emission properties of the massive, close
binary WR 20a is discussed. Located near the cluster core of Westerlund 2, WR
20a is composed of two nearly identical Wolf- Rayet stars of 82 and 83 solar
masses orbiting with a period of only 3.7 days. Although Chandra observations
were taken during the secondary optical eclipse, the X-ray light curve shows no
signs of a flux decrement. In fact, WR 20a appears slightly more X-ray luminous
and softer during the optical eclipse, opposite to what has been observed in
other binary systems. To aid in our interpretation of the data, we compare with
the results of hydrodynamical simulations using the adaptive mesh refinement
code Mezcal that includes radiative cooling and a radiative acceleration force
term. It is shown that the X-ray emission can be successfully explained in
models where the wind-wind collision interface in this system occurs while the
outflowing material is still being accelerated. Consequently, WR 20a serves as
a critical test-case for how radiatively-driven stellar winds initiate and
interact. Our models not only procure a robust description of current Chandra
data, which cover the orbital phases between 0.3 to 0.6, but provide detailed
predictions over the entire orbit. | astro-ph_HE |
GeV observations of the extended pulsar wind nebulae constrain the
pulsar interpretations of the cosmic-ray positron excess: It has long been suggested that nearby pulsars within $\sim 1 \,{\rm kpc}$
are the leading candidate of the 10-500 GeV cosmic-ray positron excess measured
by PAMELA and other experiments. The recent measurement of surface brightness
profile of TeV nebulae surrounding Geminga and PSR~B0656+14 by the
High-Altitude Water Cherenkov Observatory (HAWC) suggests inefficient diffusion
of particles from the sources, giving rise to a debate on the pulsar
interpretation of the cosmic-ray positron excess. Here we argue that GeV
observations provide more direct constraints on the positron density in the TeV
nebulae in the energy range of 10-500 GeV and hence on the origin of the
observed positron excess. Motivated by this, we search for GeV emission from
the TeV nebulae with the \textsl{Fermi} Large Area Telescope (LAT). No
spatially-extended GeV emission is detected from these two TeV nebulae in the
framework of two-zone diffusion spatial templates, suggesting a relatively low
density of GeV electrons/positrons in the TeV nebulae. A joint modelling of the
data from HAWC and \textsl{Fermi}-LAT disfavors Geminga and PSR~B0656+14 as the
dominant source of the positron excess at $\sim 50-500$ GeV for the usual
Kolmogorov-type diffusion, while for an energy-independent diffusion, a
dominant part of the positron excess contributed by them cannot be ruled out by
the current data. | astro-ph_HE |
Electron-positron flows around magnetars: The twisted magnetospheres of magnetars must sustain a persistent flow of
electron-positron plasma. The flow dynamics is controlled by the radiation
field around the hot neutron star. The problem of plasma motion in the
self-consistent radiation field is solved using the method of virtual beams.
The plasma and radiation exchange momentum via resonant scattering and
self-organize into the "radiatively locked" outflow with a well-defined,
decreasing Lorentz factor. There is an extended zone around the magnetar where
the plasma flow is ultra-relativistic; its Lorentz factor is self-regulated so
that it can marginally scatter thermal photons. The flow becomes slow and
opaque in an outer equatorial zone, where the decelerated plasma accumulates
and annihilates; this region serves as a reflector for the thermal photons
emitted by the neutron star. The e+- flow carries electric current, which is
sustained by a moderate induced electric field. The electric field maintains a
separation between the electron and positron velocities, against the will of
the radiation field. The two-stream instability is then inevitable, and the
induced turbulence can generate low-frequency emission. In particular, radio
emission may escape around the magnetic dipole axis of the star. Most of the
flow energy is converted to hard X-ray emission, which is examined in the
accompanying paper. | astro-ph_HE |
A Consistent Modeling of Neutrino-driven Wind with Accretion Flow onto a
Protoneutron Star and its Implications for $^{56}$Ni Production: Details of the explosion mechanism of core-collapse supernovae (CCSNe) are
not yet fully understood. There is now an increasing number of successful
examples of reproducing explosions in the first-principles simulations, which
have shown a slow increase of explosion energy. However, it was recently
pointed out that the growth rates of the explosion energy of these simulations
are insufficient to produce enough $^{56}$Ni mass to account for observations.
We refer to this issue as the `nickel mass problem' (Ni problem, hereafter) in
this paper. The neutrino-driven wind is suggested as one of the most promising
candidates for the solution to the Ni problem in previous literature, but a
multi-dimensional simulation for this is computationally too expensive to allow
long-term investigations. In this paper, we first built a consistent model of
the neutrino-driven wind with an accretion flow onto a protoneutron star (PNS),
by connecting a steady-state solution of the neutrino-driven wind and a
phenomenological mass accretion model. Comparing the results of our model with
the results of first-principles simulations, we find that the total ejectable
amount of the neutrino-driven wind is roughly determined within $\sim$ 1 sec
from the onset of the explosion and the supplementable amount at a late phase
($t_e \gtrsim 1$ sec) remains $M_\mathrm{ej} \lesssim 0.01M_\odot$ at most. Our
conclusion is that it is difficult to solve the Ni problem, by continuous
injection of $^{56}$Ni by the neutrino-driven wind. We suggest that the total
amount of synthesized $^{56}$Ni can be estimated robustly if simulations are
followed up to $\sim 2$ seconds. | astro-ph_HE |
Ejection of Double knots from the radio core of PKS 1510--089 during the
strong gamma-ray flares in 2015: PKS 1510--089 is a bright and active $\gamma$-ray source that showed strong
and complex $\gamma$-ray flares in mid-2015 during which the Major Atmospheric
Gamma Imaging Cherenkov telescopes detected variable very high energy (VHE;
photon energies $>$100 GeV) emission. We present long-term multi-frequency
radio, optical, and $\gamma$-ray light curves of PKS 1510--089 from 2013 to
2018, and results of an analysis of the jet kinematics and linear polarization
using 43 GHz Very Long Baseline Array data observed between late 2015 and
mid-2017. We find that a strong radio flare trails the $\gamma$-ray flares in
2015, showing an optically thick spectrum at the beginning and becoming
optically thin over time. Two laterally separated knots of emission are
observed to emerge from the radio core nearly simultaneously during the
$\gamma$-ray flares. We detect an edge-brightened linear polarization near the
core in the active jet state in 2016, similar to the quiescent jet state in
2008--2013. These observations indicate that the $\gamma$-ray flares may
originate from compression of the knots by a standing shock in the core and the
jet might consist of multiple complex layers showing time-dependent behavior,
rather than of a simple structure of a fast jet spine and a slow jet sheath. | astro-ph_HE |
Multi-messenger searches via IceCube's high-energy neutrinos and
gravitational-wave detections of LIGO/Virgo: We summarize initial results for high-energy neutrino counterpart searches
coinciding with gravitational-wave events in LIGO/Virgo's GWTC-2 catalog using
IceCube's neutrino triggers. We did not find any statistically significant
high-energy neutrino counterpart and derived upper limits on the
time-integrated neutrino emission on Earth as well as the isotropic equivalent
energy emitted in high-energy neutrinos for each event. | astro-ph_HE |
Analysis of a State Changing Supersoft X-ray Source in M31: We report on observations of a luminous supersoft X-ray source (SSS) in M31,
r1-25, that has exhibited spectral changes to harder X-ray states. We document
these spectral changes. In addition, we show that they have important
implications for modeling the source. Quasisoft states in a source that has
been observed as an SSS represent a newly- discovered phenomenon. We show how
such state changers could prove to be examples of unusual black hole or neutron
star accretors. Future observations of this and other state changers can
provide the information needed to determine the nature(s) of these intriguing
new sources. | astro-ph_HE |
Primordial Black Holes having Gravitomagnetic Monopole: A primordial black hole (PBH) is thought to be made of the regular matter or
ordinary mass ($M$) only, and hence could have already been decayed due to the
Hawking radiation if its initial ordinary mass were $\lesssim 5 \times 10^{11}$
kg. Here, we study the role of gravitomagnetic monopole for the evaporation of
PBHs, and propose that the lower energy PBHs (equivalent to ordinary mass $M <<
5\times 10^{11}$ kg) could still exist in our present Universe, if it has
gravitomagnetic monopole. If a PBH was initially made of both regular matter
and gravitomagnetic monopole, the regular matter could decay away due to the
Hawking radiation. The remnant gravitomagnetic monopole might not entirely
decay, which could still be found as a PBH in the form of the pseudo
`mass-energy'. If a PBH with $M \gtrsim 5 \times 10^{11}$ kg is detected, one
may not be able to conclude if it has gravitomagnetic monopole. But, a
plausible detection of a relatively low energy (equivalent to $2.176 \times
10^{-8}$ kg $< M \lesssim 5\times10^{11}$ kg) PBH in future may imply the
existence of a gravitomagnetic monopole PBH, which may or may not contain the
ordinary mass. | astro-ph_HE |
Discovery and Follow-up of ASASSN-23bd (AT 2023clx): The Lowest Redshift
and Least Luminous Tidal Disruption Event To Date: We report the All-Sky Automated Survey for SuperNovae discovery of the tidal
disruption event (TDE) ASASSN-23bd (AT 2023clx) in NGC 3799, a LINER galaxy
with no evidence of strong AGN activity over the past decade. With a redshift
of $z = 0.01107$ and a peak UV/optical luminosity of $(5.4\pm0.4)\times10^{42}$
erg s$^{-1}$, ASASSN-23bd is the lowest-redshift and least-luminous TDE
discovered to date. Spectroscopically, ASASSN-23bd shows H$\alpha$ and He I
emission throughout its spectral time series, and the UV spectrum shows
nitrogen lines without the strong carbon and magnesium lines typically seen for
AGN. Fits to the rising ASAS-SN light curve show that ASASSN-23bd started to
brighten on MJD 59988$^{+1}_{-1}$, $\sim$9 days before discovery, with a nearly
linear rise in flux, peaking in the $g$ band on MJD $60000^{+3}_{-3}$. Scaling
relations and TDE light curve modelling find a black hole mass of $\sim$10$^6$
$M_\odot$, which is on the lower end of supermassive black hole masses.
ASASSN-23bd is a dim X-ray source, with an upper limit of
$L_{0.3-10\,\mathrm{keV}} < 1.0\times10^{40}$ erg s$^{-1}$ from stacking all
\emph{Swift} observations prior to MJD 60061, but with soft ($\sim 0.1$ keV)
thermal emission with a luminosity of $L_{0.3-2
\,\mathrm{keV}}\sim4\times10^{39}$ erg s$^{-1}$ in \emph{XMM-Newton}
observations on MJD 60095. The rapid $(t < 15$ days) light curve rise, low
UV/optical luminosity, and a luminosity decline over 40 days of $\Delta
L_{40}\approx-0.7$ make ASASSN-23bd one of the dimmest TDEs to date and a
member of the growing ``Low Luminosity and Fast'' class of TDEs. | astro-ph_HE |
Estimating the maximum gravitational mass of nonrotating neutron stars
from the GW170817/GRB 170817A/AT2017gfo observation: Assuming that the differential rotation of the massive neutron star (NS)
formed in the double NS (DNS) mergers has been effectively terminated by the
magnetic braking and a uniform rotation has been subsequently established
(i.e., a supramassive NS is formed), we analytically derive in this work an
approximated expression for the critical total gravitational mass ($M_{\rm
tot,c}$) to form supramassive NS (SMNS) in the DNS mergers, benefited from some
equation of state (EoS) insensitive relationships. The maximum gravitational
mass of the nonrotating NSs ($M_{\rm TOV}$) as well as the dimensionless
angular momentum of the remnant ($j$) play the dominant roles in modifying
$M_{\rm tot,c}$, while the radius and mass differences of the premerger NSs do
not. The GW170817/GRB 170817A/AT2017gfo observations have provided so far the
best opportunity to quantitatively evaluate $M_{\rm TOV}$. Supposing the
central engine for GRB 170817A is a black hole quickly formed in the collapse
of an SMNS, we find $M_{\rm TOV}=2.13^{+0.09}_{-0.08}M_\odot$ (68.3%
credibility interval, including also the uncertainties of the EoS insensitive
relationships), which is consistent with the constraints set by current NS mass
measurements. | astro-ph_HE |
The coalescence rates of double black holes: We present the summary of the recent investigations of double black hole
binaries in context of their formation and merger rates. In particular we
discuss the spectrum of black hole masses, the formation scenarios in the local
Universe and the estimates of detection rates for gravitational radiation
detectors like LIGO and VIRGO. Our study is based on observed properties of
known Galactic and extra-galactic stellar mass black holes and evolutionary
predictions. We argue that the binary black holes are the most promising source
of gravitational radiation. | astro-ph_HE |
Patterns in the multi-wavelength behavior of candidate neutrino blazars: Motivated by the identification of the blazar TXS 0506+056 as the first
promising high-energy neutrino counterpart candidate, we search for additional
neutrino blazars candidates among the Fermi-LAT detected blazars.
We investigate the multi-wavelength behavior from radio to GeV gamma rays of
blazars found to be in spatial coincidence with single high-energy neutrinos
and lower-energy neutrino flare candidates. In addition, we compare the average
gamma-ray emission of the potential neutrino-emitting sources to the entire
sample of gamma-ray blazars. We find that neutrino-emitting blazar candidates
are statistically compatible with both hypothesis of a linear correlation and
of no correlation between neutrino and gamma-ray energy flux. | astro-ph_HE |
Analysis of the duration$-$hardness ratio plane of gamma-ray bursts with
skewed distributions: It was recently shown that the $T_{90}-H_{32}$ distributions of gamma-ray
bursts from CGRO/BATSE and Fermi/GBM are well described by a mixture of only
two skewed components, making the presumed third, intermediate class
unnecesary. The Swift/BAT, Konus-Wind, RHESSI and Suzaku/WAM data sets are
found to be consistent with a two-class description as well. | astro-ph_HE |
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