470 research outputs found
Underdetermined-order recursive least-squares adaptive filtering: The concept and algorithms
Published versio
Timing and X-ray Spectral Features of Swift J1626.6-5156
In this paper, we extend timing analysis of Baykal et al. (2010) of \src
using RXTE-PCA observations between MJD 53724 and MJD 55113 together with a
Chandra-ACIS observation on MJD 54897 with a 20 ks exposure. We also present
X-ray spectral analysis of these RXTE and Chandra observations. We find that
the spin-up rate of the source is correlated with the X-ray flux. Using this
correlation, we estimate the distance and surface magnetic field of the source
as kpc and Gauss respectively. From the spectral
analysis, we found that power law index increases and Hydrogen column density
decreases with decreasing flux.Comment: Revised version; 12 pages, 4 figures, accepted for publication in
MNRA
A new family of blind adaptive equalization algorithms
Published versio
Sliding window adaptive fast QR and QR-lattice algorithms
Published versio
Superfluid Friction and Late-time Thermal Evolution of Neutron Stars
The recent temperature measurements of the two older isolated neutron stars
PSR 1929+10 and PSR 0950+08 (ages of and yr,
respectively) indicate that these objects are heated. A promising candidate
heat source is friction between the neutron star crust and the superfluid it is
thought to contain. We study the effects of superfluid friction on the
long-term thermal and rotational evolution of a neutron star. Differential
rotation velocities between the superfluid and the crust (averaged over the
inner crust moment of inertia) of rad s for PSR
1929+10 and rad s for PSR 0950+08 would account for their
observed temperatures. These differential velocities could be sustained by
pinning of superfluid vortices to the inner crust lattice with strengths of
1 MeV per nucleus. Pinned vortices can creep outward through thermal
fluctuations or quantum tunneling. For thermally-activated creep, the coupling
between the superfluid and crust is highly sensitive to temperature. If pinning
maintains large differential rotation ( rad s), a feedback
instability could occur in stars younger than yr causing
oscillations of the temperature and spin-down rate over a period of . For stars older than yr, however, vortex creep occurs
through quantum tunneling, and the creep velocity is too insensitive to
temperature for a thermal-rotational instability to occur. These older stars
could be heated through a steady process of superfluid friction.Comment: 26 pages, 1 figure, submitted to Ap
Viscous timescale in high mass X-ray binaries
Context: Low mass X-ray binaries were found to have very low frequency breaks
in their power density spectra below which the power density spectra are nearly
in white noise structure and at higher frequencies they approximately follow
the law.
Aims: In 2005, Gilfanov and Arefiev studied X-ray variability of persistent
LMXBs in the Hz frequency range and
To determine whether high mass X-ray binary power density spectra have
similar properties and the findings for low mass X-ray binaries are also valid
for high mass binaries, we analyzed the time series of high mass X-ray binary
sources produced by All Sky Monitor of Rossi X-ray Timing Explorer.
Method: We obtained the power density spectra of the high mass X-ray binaries
using the cosine transform of autocorrelation function.
Results: We identified break frequencies for seven sources, namely OAO
1657-415, SS 433, Vela X-1, SMC X-1, 4U 1700-377, GX 301-2, and LMC X-1. The
normalized break frequencies with respect to the orbital frequency
() for sources OAO 1657-415, SS 433, SMC X-1 and LMC X-1
are consistent with those of Roche lobe overflow systems. The other high mass
X-ray binary systems, Vela X-1, GX 301-2, and 4U 1700-377, however, have larger
break frequency ratios, , which are indicative of short
viscous times. These are all wind-accreting sources and the stellar winds in
the systems allow the formation of only short radius discs.
Consequently, we qualitatively distinguished the Roche lobe overflow binaries
from the wind accreting system by comparing their normalized break frequencies.Comment: 9 pages, 5 figures, accepted by A&
Post-Glitch RXTE-PCA Observations of the Vela Pulsar
We report the results of analysis of observations of the Vela Pulsar by PCA
on RXTE. Our data consists of two parts. The first part contains observations
at 1, 4, and 9 days after the glitch in 1996 and has 27000 sec. total exposure
time. The second part of observations were performed three months after this
glitch and have a total exposure time of 93000 sec. We found pulsations in both
sets. The observed spectrum is a power-law with no apparent change in flux or
count rate. The theoretical expectations of increase in flux due to internal
heating after a glitch are smaller than the uncertainty of the observations.Comment: 6 pages, 5 figures in 9 ps/eps files. Accepted for publication in A&A
Main Journa
Cylindrically Symmetric Vacuum Solutions in Higher Dimensional Brans-Dicke Theory
Higher dimensional, static, cylindrically symmetric vacuum solutions with and
without a cosmological constant in the Brans-Dicke theory are presented. We
show that, for a negative cosmological constant and for specific values of the
parameters, a particular subclass of these solutions include higher dimensional
topological black hole-type solutions with a flat horizon topology. We briefly
extend our discussion to stationary vacuum and vacuum solutions.Comment: V3: Published Versio
Residual echo signal in critically sampled subband acoustic echo cancellers based on IIR and FIR filter banks
Published versio
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