423 research outputs found
Variations in the Cyclotron Resonant Scattering Features during 2011 outburst of 4U 0115+63
We study the variations in the Cyclotron Resonant Scattering Feature (CRSF)
during 2011 outburst of the high mass X-ray binary 4U 0115+63 using
observations performed with Suzaku, RXTE, Swift and INTEGRAL satellites. The
wide-band spectral data with low energy coverage allowed us to characterize the
broadband continuum and detect the CRSFs. We find that the broadband continuum
is adequately described by a combination of a low temperature (kT ~ 0.8 keV)
blackbody and a power-law with high energy cutoff (Ecut ~ 5.4 keV) without the
need for a broad Gaussian at ~ 10 keV as used in some earlier studies. Though
winds from the companion can affect the emission from the neutron star at low
energies (< 3 keV), the blackbody component shows a significant presence in our
continuum model. We report evidence for the possible presence of two
independent sets of CRSFs with fundamentals at ~ 11 keV and ~ 15 keV. These two
sets of CRSFs could arise from spatially distinct emitting regions. We also
find evidence for variations in the line equivalent widths, with the 11 keV
CRSF weakening and the 15 keV line strengthening with decreasing luminosity.
Finally, we propose that the reason for the earlier observed anti-correlation
of line energy with luminosity could be due to modelling of these two
independent line sets (~ 11 keV and ~ 15 keV) as a single CRSF.Comment: 12 pages, 8 figures (4 in colour), 6 tables. Accepted for publication
in MNRAS. Typos corrected, Figure 8 changed and some changes to draf
Voltage and Frequency Dependence of Electroluminescence in Some ZnS Mixed CaS and CaS Mixed ZnS Phosphors
Broadband X-ray emission and the reality of the broad iron line from the Neutron Star - White Dwarf X-ray binary 4U 1820-30
Broad relativistic iron lines from neutron star X-ray binaries are important
probes of the inner accretion disk. The X-ray reflection features can be
weakened due to strong magnetic fields or very low iron abundances such as is
possible in X-ray binaries with low mass, first generation stars as companions.
Here we investigate the reality of the broad iron line detected earlier from
the neutron star low mass X-ray binary 4U~1820--30 with a degenerate helium
dwarf companion. We perform a comprehensive, systematic broadband spectral
study of the atoll source using \suzaku{} and simultaneous \nustar{} \&
\swift{} observations. We have used different continuum models involving
accretion disk emission, thermal blackbody and thermal Comptonization of either
disk or blackbody photons. The \suzaku{} data show positive and negative
residuals in the region of iron K band. These features are well described by
two absorption edges at 7.67\pm0.14\kev and 6.93\pm0.07\kev or partial
covering photoionized absorption or by blurred reflection. Though, the
simultaneous \swift{} and \nustar{} data do not clearly reveal the emission or
absorption features, the data are consistent with the presence of either
absorption or emission features. Thus, the absorption based models provide an
alternative to the broad iron line or reflection model. The absorption features
may arise in winds from the inner accretion disk. The broadband spectra appear
to disfavour continuum models in which the blackbody emission from the neutron
star surface provides the seed photons for thermal Comptonization. Our results
suggest emission from a thin accretion disk (kT_{disk} \sim 1\kev),
Comptonization of disk photons in a boundary layer most likely covering a large
fraction of the neutron star surface and innermost parts of the accretion disk,
and blackbody emission (kT_{bb} \sim 2\kev) from the polar regions.Comment: 12 pages, 8 figures, 5 tables. Accepted for publication in MNRA
The Hard X-ray emission of the blazar PKS 2155--304
The synchrotron peak of the X-ray bright High Energy Peaked Blazar (HBL) PKS
2155304 occurs in the UV-EUV region and hence its X-ray emission (0.6--10
keV) lies mostly in the falling part of the synchrotron hump. We aim to study
the X-ray emission of PKS 2155304 during different intensity states in
20092014 using XMMNewton satellite. We studied the spectral curvature of
all of the observations to provide crucial information on the energy
distribution of the non-thermal particles. Most of the observations show
curvature or deviation from a single power-law and can be well modeled by a log
parabola model. In some of the observations, we find spectral flattening after
6 keV. In order to find the possible origin of the X-ray excess, we built the
Multi-band Spectral Energy distribution (SED). We find that the X-ray excess in
PKS 2155--304 is difficult to fit in the one zone model but, could be easily
reconciled in the spine/layer jet structure. The hard X-ray excess can be
explained by the inverse Comptonization of the synchrotron photons (from the
layer) by the spine electrons.Comment: 14 pages, 7 Figures, Accepted for publication in Ap
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