197 research outputs found
ROSAT HRI catalogue of X-ray sources in the LMC region
All 543 pointed observations of the ROSAT High Resolution Imager (HRI) with
exposure times higher than 50 sec in a field of 10 deg x 10 deg covering the
Large Magellanic Cloud (LMC) were analyzed. A catalogue was produced containing
397 X-ray sources with their properties measured by the HRI. The list was
cross-correlated with the ROSAT Position Sensitive Propotional Counter (PSPC)
source catalogue presented by Haberl & Pietsch (1999), the SIMBAD data base,
and the TYCHO catalogue. 138 HRI sources are contained in the PSPC catalogue.
The spatial resolution of the HRI was higher than that of the PSPC and the
source position could be determined with errors mostly smaller than 15 arcsec
which are dominated by systematic attitude errors. 94 HRI sources were
identified with known objects based on their positional coincidence and X-ray
properties. The catalogue contains 39 foreground stars, 24 supernova remnants
(SNRs), five supersoft sources (SSSs), nine X-ray binaries (XBs), and nine AGN
well known from literature. Another eight sources were identified with known
candidates for these source classes. Additional 21 HRI sources are suggested in
the present work as candidates for SNR, X-ray binary in the LMC, or background
AGN because of their extent, hardness ratios, X-ray to optical flux ratio, or
flux variability.Comment: 22 pages, 8 figures, 4 table
The Bursting Behavior of 4U 1728-34: Parameters of a Neutron Star and Geometry of a NS-disk system
We analyze a set of Type I X-ray bursts from the low mass X-ray binary 4U
1728 -34, observed with Rossi X-ray Timing Explorer (RXTE). and we implement an
analytical model of X-ray spectral formation in the neutron star (NS)
atmosphere during a burst. We infer the dependence of the neutron star mass and
radius with respect to the assumed distance to the system using an analytical
model of X-ray burst spectral formation. The model behavior clearly indicates
that the burster atmosphere is helium-dominated. Our results strongly favor the
soft equation of state (EOS) of NS for 4U 1728-34. We find that distance to the
source should be within 4.5-5.0 kpc range. We obtain rather narrow constrains
for the NS radius in 8.7-9.7 km range and interval 1.2-1.6 solar masses for NS
mass for this particular distance range.
We uncover a temporal behavior of red-shift corrected burst flux for the
radial expansion episodes and we put forth a dynamical evolution scenario for
the NS--accretion disk geometry during which an expanded envelope affects the
accretion disk and increases the area of the neutron star exposed to the Earth
observer. Our scenario enables us to explain the timing characteristics and
peak flux variation observed during the burst expansion stage, which is now
believed to be common phenomenon. In the framework of this scenario we provide
a new method for the estimation of the inclination angle which leads to the
value of 50 degrees for 4U 1728-34 .Comment: 8 pages, 3 figures and one table, accepted for publication in the
Astrophysical Journal Letter
Detection of a cyclotron line in SXP 15.3 during its 2017 outburst
We report the results of AstroSat and NuSTAR observations of the Be/X-ray
binary pulsar SXP 15.3 in the Small Magellanic Cloud during its outburst in
late 2017, when the source reached a luminosity level of ~ 10^{38} erg s^{-1},
close to the Eddington limit. The unprecedented broadband coverage of the
source allowed us to perform timing and spectral analysis between 3 and 80 keV.
The pulse profile exhibits a significant energy dependence, and morphs from a
double peaked profile to a single broad pulse at energies >15 keV. This can be
explained by a spectral hardening during an intensity dip seen between the two
peaks of the pulse profile. We detect a Cyclotron Resonance Scattering Feature
(CRSF) at ~5 keV in the X-ray spectrum, independent of the choice of the
continuum model. This indicates a magnetic field strength of 6x10^{11} G for
the neutron star.Comment: 5 pages, 6 figures, accepted for publication in MNRAS Letter
An Optical Study of Two VY Sculptoris-Type Cataclysmic Binary Stars: V704 And and RX J2338+431
We report observations of the known cataclysmic variable star (CV) V704 And,
and also confirm that the optical counterpart of the ROSAT Galactic Plane
Survey source RX J2338+431 is a heretofore-neglected CV. Photometric and
spectroscopic observations from MDM Observatory show both systems to be
novalike variables that exhibit dips of 4-5 magnitudes from their mean
brightnesses, establishing them as members of the VY~Scl subclass. From
high-state emission-line radial velocities, we determine orbital periods of
0.151424(3) d (3.63 hr) for V704 And and 0.130400(1) d (3.13 hr) for RX
J2338+431. In V704 And, we find that the H-alpha emission-line measures cluster
into distinct regions on a plot of equivalent width versus full width at
half-maximum, which evidently correspond to high, intermediate, and low
photometric states. This allows us to assign spectra to photometric states when
contemporaneous photometry is not available, an apparently novel method that
may be useful in studies of other novalikes. Our low-state spectra of RX
J2338+431 show features of an M-type secondary star, from which we estimate a
distance of 890 +- 200 pc, in good agreement with the Gaia DR2 parallax.Comment: Accepted for Astronomical Journa
Probing the Interstellar Dust towards the Galactic Centre: Dust Scattering Halo around AX J1745.6-2901
AX J1745.6-2901 is an X-ray binary located at only 1.45 arcmin from Sgr A*,
showcasing a strong X-ray dust scattering halo. We combine Chandra and
XMM-Newton observations to study the halo around this X-ray binary. Our study
shows two major thick dust layers along the line of sight (LOS) towards AX
J1745.6-2901. The LOS position and of these two layers depend on the
dust grain models with different grain size distribution and abundances. But
for all the 19 dust grain models considered, dust Layer-1 is consistently found
to be within a fractional distance of 0.11 (mean value: 0.05) to AX
J1745.6-2901 and contains only (19-34)% (mean value: 26%) of the total LOS
dust. The remaining dust is contained in Layer-2, which is distributed from the
Earth up to a mean fractional distance of 0.64. A significant separation
between the two layers is found for all the dust grain models, with a mean
fractional distance of 0.31. Besides, an extended wing component is discovered
in the halo, which implies a higher fraction of dust grains with typical sizes
590 \AA\ than considered in current dust grain models. Assuming AX
J1745.6-2901 is 8 kpc away, dust Layer-2 would be located in the Galactic disk
several kpc away from the Galactic Centre (GC). The dust scattering halo biases
the observed spectrum of AX J1745.6-2901 severely in both spectral shape and
flux, and also introduces a strong dependence on the size of the instrumental
point spread function and the source extraction region. We build Xspec models
to account for this spectral bias, which allow us to recover the intrinsic
spectrum of AX J1745.6-2901 free from dust scattering opacity. If dust Layer-2
also intervenes along the LOS to Sgr A* and other nearby GC sources, a
significant spectral correction for the dust scattering opacity would be
necessary for all these GC sources.Comment: 20 pages, published by MNRAS; revised values in Table-1 and Table-B
Effects of Interstellar Dust Scattering on the X-ray Eclipses of the LMXB AX J1745.6-2901 in the Galactic Center
AX J1745.6-2901 is an eclipsing low mass X-ray binary (LMXB) in the Galactic
Centre (GC). It shows significant X-ray excess emission during the eclipse
phase, and its eclipse light curve shows an asymmetric shape. We use archival
XMM-Newton and Chandra observations to study the origin of these peculiar X-ray
eclipsing phenomena. We find that the shape of the observed X-ray eclipse light
curves depends on both photon energy and the shape of the source extraction
region, and also shows differences between the two instruments. By performing
detailed simulations for the time-dependent X-ray dust scattering halo, as well
as directly modelling the observed eclipse and non-eclipse halo profiles of AX
J1745.6-2901, we obtained solid evidence that its peculiar eclipse phenomena
are indeed caused by the X-ray dust scattering in multiple foreground dust
layers along the line-of-sight (LOS). The apparent dependence on the
instruments is caused by different instrumental point-spread-functions. Our
results can be used to assess the influence of dust scattering in other
eclipsing X-ray sources, and raise the importance of considering the timing
effects of dust scattering halo when studying the variability of other X-ray
sources in the GC, such as Sgr A*. Moreover, our study of halo eclipse
reinforces the existence of a dust layer local to AX J1745.6-2901 as reported
by Jin et al. (2017), as well as identifying another dust layer within a few
hundred parsecs to Earth, containing up to several tens of percent LOS dust,
which is likely to be associated with the molecular clouds in the Solar
neighbourhood. The remaining LOS dust is likely to be associated with the
molecular clouds located in the Galactic disk in-between.Comment: 25 pages, 18 figures, 5 tables, accepted by MNRA
Spectral and temporal properties of RX J0520.5-6932 (LXP 8.04) during a type-I outburst
We observed RX J0520.5-6932 in the X-rays and studied the optical light curve
of its counterpart to verify it as a Be/X-ray binary. We performed an
XMM-Newton anticipated target of opportunity observation in January 2013 during
an X-ray outburst of the source in order to search for pulsations and derive
its spectral properties. We monitored the source with Swift to follow the
evolution of the outburst and to look for further outbursts to verify the
regular pattern seen in the optical light curve with a period of ~24.4 d. The
XMM-Newton EPIC light curves show coherent X-ray pulsations with a period of
8.035331(15) s (1 sigma). The X-ray spectrum can be modelled by an absorbed
power law with photon index of ~0.8, an additional black-body component with
temperature of ~0.25 keV and an Fe K line. Phase-resolved X-ray spectroscopy
reveals that the spectrum varies with pulse phase. We confirm the
identification of the optical counterpart within the error circle of XMM-Newton
at an angular distance of ~0.8 arcsec, which is an O9Ve star with known Halpha
emission. By analyzing the combined data from three OGLE phases we derived an
optical period of 24.43 d.The X-ray pulsations and long-term variability, as
well as the properties of the optical counterpart, confirm that RX J0520.5-6932
is a Be/X-ray binary pulsar in the Large Magellanic Cloud. Based on the X-ray
monitoring of the source we conclude that the event in January 2013 was a
moderately bright type-I X-ray outburst, with a peak luminosity of 1.79e36
erg/s.Comment: 10 pages, 9 figures, accepted A&
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