146 research outputs found
Registration of the First Thermonuclear X-ray Burst from AX J1754.2-2754
During the analysis of the INTEGRAL observatory archival data we found a
powerful X-ray burst, registered by JEM-X and IBIS/ISGRI telescopes on April
16, 2005 from a weak and poorly known source AX J1754.2-2754. Analysis of the
burst profiles and spectrum shows, that it was a type I burst, which result
from thermonuclear explosion on the surface of nutron star. It means that we
can consider AX J1754.2-2754 as an X-ray burster. Certain features of burst
profile at its initial stage witness of a radiation presure driven strong
expansion and a corresponding cooling of the nutron star photosphere. Assuming,
that the luminosity of the source at this phase was close to the Eddington
limit, we estimated the distance to the burst source d=6.6+/-0.3 kpc (for
hidrogen atmosphere of the neutron star) and d=9.2+/-0.4 kpc (for helium
atmosphere).Comment: 12 pages, 6 figure
IXPE Mirror Module Assemblies
Expected to launch in 2021 Spring, the Imaging X-ray Polarimetry Explorer (IXPE) is a NASA Astrophysics Small Explorer Mission with significant contributions from the Italian space agency (ASI). The IXPE observatory features three identical x-ray telescopes, each comprised of a 4-m-focal-length mirror module assembly (MMA, provided by NASA Marshall Space Flight Center) that focuses x rays onto a polarization-sensitive, imaging detector (contributed by ASI-funded institutions). This paper summarizes the MMAs design, fabrication, alignment and assembly, expected performance, and calibration plans
The ART-XC telescope on board the SRG observatory
ART-XC (Astronomical Roentgen Telescope - X-ray Concentrator) is the hard
X-ray instrument with grazing incidence imaging optics on board the
Spektr-Roentgen-Gamma (SRG) observatory. The SRG observatory is the flagship
astrophysical mission of the Russian Federal Space Program, which was
successively launched into orbit around the second Lagrangian point (L2) of the
Earth-Sun system with a Proton rocket from the Baikonur cosmodrome on 13 July
2019. The ART-XC telescope will provide the first ever true imaging all-sky
survey performed with grazing incidence optics in the 4-30 keV energy band and
will obtain the deepest and sharpest map of the sky in the energy range of 4-12
keV. Observations performed during the early calibration and performance
verification phase as well as during the on-going all-sky survey that started
on 12 Dec. 2019 have demonstrated that the in-flight characteristics of the
ART-XC telescope are very close to expectations based on the results of ground
calibrations. Upon completion of its 4-year all-sky survey, ART-XC is expected
to detect ~5000 sources (~3000 active galactic nuclei, including heavily
obscured ones, several hundred clusters of galaxies, ~1000 cataclysmic
variables and other Galactic sources), and to provide a high-quality map of the
Galactic background emission in the 4-12 keV energy band. ART-XC is also well
suited for discovering transient X-ray sources. In this paper, we describe the
telescope, results of its ground calibrations, major aspects of the mission,
the in-flight performance of ART-XC and first scientific results.Comment: 19 pages, 30 figures, accepted for publication in Astronomy and
Astrophysic
SRG/ART-XC and NuSTAR observations of the X-ray pulsar GRO J1008-57 in the lowest luminosity state
We report results of the first broadband observation of the transient X-ray
pulsar GRO J1008-57 performed in the quiescent state. Observations were
conducted quasi-simultaneously with the Mikhail Pavlinsky ART-XC telescope on
board SRG and NuSTAR right before the beginning of a Type I outburst. GRO
J1008-57 was detected in the state with the lowest observed luminosity around
several erg s and consequently accreting from the cold
disk. Timing analysis allowed to significantly detect pulsations during this
state for the first time. The observed pulsed fraction of about 20\% is,
however, almost three times lower than in brighter states when the accretion
proceeds through the standard disk. We traced the evolution of the broadband
spectrum of the source on a scale of three orders of magnitude in luminosity
and found that at the lowest luminosities the spectrum transforms into the
double-hump structure similarly to other X-ray pulsars accreting at low
luminosities (X Persei, GX 304-1, A0535+262) reinforcing conclusion that this
spectral shape is typical for these objects.Comment: 8 pages, 5 figures, accepted to Ap
Luminosity Function of High-Mass X-ray Binaries and Anisotropy in the Distribution of Active Galactic Nuclei toward the Large Magellanic Cloud
In 2003-2012, the INTEGRAL observatory has performed long-term observations
of the Large Magellanic Cloud (LMC). At present, this is one of the deepest
hard X-ray (20-60 keV) surveys of extragalactic fields in which more than 20
sources of different natures have been detected. We present the results of a
statistical analysis of the population of high-mass X-ray binaries in the LMC
and active galactic nuclei (AGNs) observed in its direction. The hard X-ray
luminosity function of high-mass X-ray binaries is shown to be described by a
power law with a slope alpha~1.8, that in agreement with the luminosity
function measurements both in the LMC itself, but made in the soft X-ray energy
band, and in other galaxies. At the same time, the number of detected AGNs
toward the LMC turns out to be considerably smaller than the number of AGNs
registered in other directions, in particular, toward the source 3C 273. The
latter confirms the previously made assumption that the distribution of matter
in the local Universe is nonuniform.Comment: 5 pages, 5 figures, will be published in Astronomy Letters, 2012,
Vol. 38, No. 8, p. 492--49
Polarized x-rays constrain the disk-jet geometry in the black hole x-ray binary Cygnus X-1
A black hole x-ray binary (XRB) system forms when gas is stripped from a normal star and accretes onto a black hole, which heats the gas sufficiently to emit x-rays. We report a polarimetric observation of the XRB Cygnus X-1 using the Imaging X-ray Polarimetry Explorer. The electric field position angle aligns with the outflowing jet, indicating that the jet is launched from the inner x-ray–emitting region. The polarization degree is 4.01 ± 0.20% at 2 to 8 kiloelectronvolts, implying that the accretion disk is viewed closer to edge-on than the binary orbit. These observations reveal that hot x-ray–emitting plasma is spatially extended in a plane perpendicular to, not parallel to, the jet axis
Search for pre-burst emission from binary neutron star mergers with Spectrum-Roentgen-Gamma
Close binary systems consisting of two neutron stars (BNS) emit gravitational
waves, that allow them to merge on timescales shorter than Hubble time. It is
widely believed, that NS-NS mergers in such systems power short gamma-ray
bursts (GRB). Several mechanisms which could lead to electromagnetic energy
release prior to a merger have been proposed. We estimate the ability to
observe the possible pre-burst emission with telescopes of
Spectrum-Roentgen-Gamma. We also investigate first such event, GRB210919A,
which fell into the field of view of the SRG telescopes less than two days
before the burst.Comment: Accepted for publication in Astronomy Letter
Monte Carlo simulations of soft proton flares: testing the physics with XMM-Newton
Low energy protons (<100-300 keV) in the Van Allen belt and the outer regions
can enter the field of view of X-ray focusing telescopes, interact with the
Wolter-I optics, and reach the focal plane. The use of special filters protects
the XMM-Newton focal plane below an altitude of 70000 km, but above this limit
the effect of soft protons is still present in the form of sudden flares in the
count rate of the EPIC instruments, causing the loss of large amounts of
observing time. We try to characterize the input proton population and the
physics interaction by simulating, using the BoGEMMS framework, the proton
interaction with a simplified model of the X-ray mirror module and the focal
plane, and comparing the result with a real observation. The analysis of ten
orbits of observations of the EPIC/pn instrument show that the detection of
flares in regions far outside the radiation belt is largely influenced by the
different orientation of the Earth's magnetosphere respect with XMM-Newton's
orbit, confirming the solar origin of the soft proton population. The Equator-S
proton spectrum at 70000 km altitude is used for the proton population entering
the optics, where a combined multiple and Firsov scattering is used as physics
interaction. If the thick filter is used, the soft protons in the 30-70 keV
energy range are the main contributors to the simulated spectrum below 10 keV.
We are able to reproduce the proton vignetting observed in real data-sets, with
a 50\% decrease from the inner to the outer region, but a maximum flux of 0.01
counts cm-2 s-1 keV-1 is obtained below 10 keV, about 5 times lower than the
EPIC/MOS detection and 100 times lower than the EPIC/pn one. Given the high
variability of the flare intensity, we conclude that an average spectrum, based
on the analysis of a full season of soft proton events is required to compare
Monte Carlo simulations with real events
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