71,389 research outputs found
Relativistic Disk Reflection in the Neutron Star X-ray Binary XTE J1709-267 with NuSTAR
We perform the first reflection study of the soft X-ray transient and Type 1
burst source XTE J1709-267 using NuSTAR observations during its 2016 June
outburst. There was an increase in flux near the end of the observations, which
corresponds to an increase from 0.04 L to 0.06
L assuming a distance of 8.5 kpc. We have separately examined
spectra from the low and high flux intervals, which were soft and show evidence
of a broad Fe K line. Fits to these intervals with relativistic disk reflection
models have revealed an inner disk radius of (where
) for the low flux spectrum and
for the high flux spectrum at the 90\% confidence level. The disk is likely
truncated by a boundary layer surrounding the neutron star or the
magnetosphere. Based on the measured luminosity and using the accretion
efficiency for a disk around a neutron star, we estimate that the theoretically
expected size for the boundary layer would be from the
neutron star's surface, which can be increased by spin or viscosity effects.
Another plausible scenario is that the disk could be truncated by the
magnetosphere. We place a conservative upper limit on the strength of the
magnetic field at the poles, assuming and , of
G, though X-ray pulsations have not been detected
from this source.Comment: Accepted for publication in ApJ, 5 pages, 4 figures, 1 table. arXiv
admin note: text overlap with arXiv:1701.0177
A short note on the presence of spurious states in finite basis approximations
The genesis of spurious solutions in finite basis approximations to operators
which possess a continuum and a point spectrum is discussed and a simple
solution for identifying these solutions is suggested
Hybrid Stars
Recently there have been important developments in the determination of
neutron star masses which put severe constraints on the composition and
equation of state (EOS) of the neutron star matter. Here we study the effect of
quark and nuclear matter mixed phase on mass radius relationship of neutron
stars employing recent models from two classes of EOS's and discuss their
implications.Comment: 3 pages LaTeX including 2 figures, macros included, Talk presented at
the IX International Symposium on Particles, Strings and Cosmology
(PASCOS'03), TIFR, Mumbai, India, January 3-8,2003. To appear in their
proceeding
Ultraviolet/X-ray variability and the extended X-ray emission of the radio-loud broad absorption line quasar PG 1004+130
We present the results of recent Chandra, XMM-Newton, and Hubble Space
Telescope observations of the radio-loud (RL), broad absorption line (BAL)
quasar PG 1004+130. We compare our new observations to archival X-ray and UV
data, creating the most comprehensive, high signal-to-noise, multi-epoch,
spectral monitoring campaign of a RL BAL quasar to date. We probe for
variability of the X-ray absorption, the UV BAL, and the X-ray jet, on
month-year timescales. The X-ray absorber has a low column density of
cm when it is assumed to be fully
covering the X-ray emitting region, and its properties do not vary
significantly between the 4 observations. This suggests the observed absorption
is not related to the typical "shielding gas" commonly invoked in BAL quasar
models, but is likely due to material further from the central black hole. In
contrast, the CIV BAL shows strong variability. The equivalent width (EW) in
2014 is EW=11.240.56 \AA, showing a fractional increase of =1.160.11 from the 2003 observation, 3183 days earlier
in the rest-frame. This places PG 1004+130 among the most highly variable BAL
quasars. By combining Chandra observations we create an exposure 2.5 times
deeper than studied previously, with which to investigate the nature of the
X-ray jet and extended diffuse X-ray emission. An X-ray knot, likely with a
synchrotron origin, is detected in the radio jet ~8 arcsec (30 kpc) from the
central X-ray source with a spatial extent of ~4 arcsec (15 kpc). No similar
X-ray counterpart to the counterjet is detected. Asymmetric, non-thermal
diffuse X-ray emission, likely due to inverse Compton scattering of Cosmic
Microwave Background photons, is also detected.Comment: 15 pages, 7 figures, 3 tables. Accepted for publication in Ap
A NuSTAR observation of disk reflection from close to the neutron star in 4U 1608-52
Studying the reflection of X-rays off the inner edge of the accretion disk in
a neutron star low-mass X-ray binary, allows us to investigate the accretion
geometry and to constrain the radius of the neutron star. We report on a NuSTAR
observation of 4U 1608-52 obtained during a faint outburst in 2014 when the
neutron star, which has a known spin frequency of 620 Hz, was accreting at
~1-2% of the Eddington limit. The 3-79 keV continuum emission was dominated by
a Gamma~2 power law, with a ~1-2% contribution from a kTbb~0.3-0.6 keV black
body component. The high-quality NuSTAR spectrum reveals the hallmarks of disk
reflection; a broad iron line peaking near 7~keV and a Compton back-scattering
hump around ~20-30 keV. Modeling the disk reflection spectrum points to a
binary inclination of i~30-40 degrees and a small `coronal' height of h<8.5
GM/c2. Furthermore, our spectral analysis suggests that the inner disk radius
extended to Rin~7-10 GM/c2, close to the innermost stable circular obit. This
constrains the neutron star radius to R<21 km and the redshift from the stellar
surface to z>0.12, for a mass of M=1.5 Msun and a spin parameter of a=0.29.Comment: 5 pages, 4 figures, 1 table, MNRAS Letters in pres
Recommended from our members
Continued evaluation of potential for geologic storage of carbon dioxide in the southeastern United States
Southern States Energy Board
Duke Energy
Santee Cooper Power
Southern CompanyBureau of Economic Geolog
X-ray and UV correlation in the quiescent emission of Cen X-4, evidence of accretion and reprocessing
We conducted the first long-term (60 days), multiwavelength (optical,
ultraviolet, and X-ray) simultaneous monitoring of Cen X-4 with daily Swift
observations, with the goal of understanding variability in the low mass X-ray
binary Cen X-4 during quiescence. We found Cen X-4 to be highly variable in all
energy bands on timescales from days to months, with the strongest quiescent
variability a factor of 22 drop in the X-ray count rate in only 4 days. The
X-ray, UV and optical (V band) emission are correlated on timescales down to
less than 110 s. The shape of the correlation is a power law with index gamma
about 0.2-0.6. The X-ray spectrum is well fitted by a hydrogen NS atmosphere
(kT=59-80 eV) and a power law (with spectral index Gamma=1.4-2.0), with the
spectral shape remaining constant as the flux varies. Both components vary in
tandem, with each responsible for about 50% of the total X-ray flux, implying
that they are physically linked. We conclude that the X-rays are likely
generated by matter accreting down to the NS surface. Moreover, based on the
short timescale of the correlation, we also unambiguously demonstrate that the
UV emission can not be due to either thermal emission from the stream impact
point, or a standard optically thick, geometrically thin disc. The spectral
energy distribution shows a small UV emitting region, too hot to arise from the
accretion disk, that we identified as a hot spot on the companion star.
Therefore, the UV emission is most likely produced by reprocessing from the
companion star, indeed the vertical size of the disc is small and can only
reprocess a marginal fraction of the X-ray emission. We also found the
accretion disc in quiescence to likely be UV faint, with a minimal contribution
to the whole UV flux.Comment: 5 pages, 4 figures, submitted to Proc. Int. Conf. Physics at the
Magnetospheric Boundary, Geneva, Switzerland (25-28 June, 2013
Daily, multiwavelength Swift monitoring of the neutron star low-mass X-ray binary Cen X-4: evidence for accretion and reprocessing during quiescence
We conducted the first long-term (60 days), multiwavelength (optical,
ultraviolet, and X-ray) simultaneous monitoring of Cen X-4 with daily Swift
observations from June to August 2012, with the goal of understanding
variability in the low mass X-ray binary Cen X-4 during quiescence. We found
Cen X-4 to be highly variable in all energy bands on timescales from days to
months, with the strongest quiescent variability a factor of 22 drop in the
X-ray count rate in only 4 days. The X-ray, UV and optical (V band) emission
are correlated on timescales down to less than 110 s. The shape of the
correlation is a power law with index gamma about 0.2-0.6. The X-ray spectrum
is well fitted by a hydrogen NS atmosphere (kT=59-80 eV) and a power law (with
spectral index Gamma=1.4-2.0), with the spectral shape remaining constant as
the flux varies. Both components vary in tandem, with each responsible for
about 50% of the total X-ray flux, implying that they are physically linked. We
conclude that the X-rays are likely generated by matter accreting down to the
NS surface. Moreover, based on the short timescale of the correlation, we also
unambiguously demonstrate that the UV emission can not be due to either thermal
emission from the stream impact point, or a standard optically thick,
geometrically thin disc. The spectral energy distribution shows a small UV
emitting region, too hot to arise from the accretion disk, that we identified
as a hot spot on the companion star. Therefore, the UV emission is most likely
produced by reprocessing from the companion star, indeed the vertical size of
the disc is small and can only reprocess a marginal fraction of the X-ray
emission. We also found the accretion disc in quiescence to likely be UV faint,
with a minimal contribution to the whole UV flux.Comment: 19 pages, 6 figures, 4 table
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