74 research outputs found
Short term pulse frequency fluctuations of OAO 1657-415 from RXTE observations
We present new X-ray observations of the high mass X-ray binary (HMXRB)
pulsar OAO 1657-415, obtained during one orbital period (10.44 days) with the
Rossi X-Ray Timing Explorer (RXTE). Using the binary orbital parameters,
obtained from Burst and Transient Source Experiment (BATSE) observations, we
resolve the fluctuations in the pulse frequency at time scales on the order of
one day for the first time. Recent BATSE results showed that OAO 1657-415 has
spin-up/down trends in its pulse frequency time series, without any correlation
with the X-luminosity at energies 20 keV (Baykal 1997). In the present RXTE
observations the source is found to be in an extended phase of spin-down. We
also find a gradual increase in the X-ray luminosity which is correlated with a
marginal spin-up episode. The marginal correlation between the gradual spin-up
(or decrease in spin-down rate) and increase in X-ray luminosity suggests that
the OAO 1657-415 is observed during a stable accretion episode where the
prograde accretion disk is formed.Comment: MNRAS (2000), vol 313, 63
X-ray Flux and Pulse Frequency Changes of Three High Mass X-ray Binary Pulsars: Vela X-1, GX 301-2 and OAO 1657-415
Using archival BATSE (Burst and Transient Source Experiment) 20-60 keV band
X-ray flux and pulse frequency time series, we look for correlations between
torque, luminosity and specific angular momentum for three high mass X-ray
binary pulsars Vela X-1, GX 301-2 and OAO 1657-415. Our results show that there
is no correlation between pulse frequency derivative and flux which may be an
indication of the absence of stable prograde accretion disk. From the strong
correlation of specific angular momentum and torque, we conclude that the
accretion geometry changes continuously as suggested by the hydrodynamic
simulations(Blondin et al. 1990).Comment: 14 pages, 9 figures, accepted for publication in Astronomy and
Astrophysic
The Timing Noise of PSR 0823+26, PSR 1706-16, PSR 1749-28, PSR 2021+51 and The Anomalous Braking Indices
We have investigated the stability of the pulse frequency second derivatives
() of PSR 0823+26, PSR 1706-16, PSR 1749-28, PSR 2021+51 which show
significant quadratic trends in their pulse frequency histories in order to
determine whether the observed second derivatives are secular or they arise as
part of noise processes. We have used TOA data extending to more than three
decades which are the longest time spans ever taken into account in pulse
timing analyses. We investigated the stability of pulse frequency second
derivative in the framework of low resolution noise power spectra (Deeter 1984)
estimated from the residuals of pulse frequency and TOA data. We have found
that the terms of these sources arise from the red torque noise in
the fluctuations of pulse frequency derivatives which may originate from the
external torques from the magnetosphere of pulsar
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
Discovery of the Orbit of the Transient X ray Pulsar SAX J2103.5+4545
Using X-ray data from the Rossi X-Ray Timing Explorer (RXTE), we carried out
pulse timing analysis of the transient X-ray pulsar SAX J2103.5+4545. An
outburst was detected by All Sky Monitor (ASM) October 25 1999 and reached a
peak X-ray brightness of 27 mCrab October 28. Between November 19 and December
27, the RXTE/PCA carried out pointed observations which provided us with pulse
arrival times. These yield an eccentric orbit (e= 0.4 \pm 0.2) with an orbital
period of 12.68 \pm 0.25 days and light travel time across the projected
semimajor axis of 72 \pm 6 sec. The pulse period was measured to be 358.62171
\pm 0.00088 s and the spin-up rate (2.50 \pm 0.15) \times 10^{-13} Hz s^{-1}.
The ASM data for the February to September 1997 outburst in which BeppoSAX
discovered SAX J2103.5+4545 (Hulleman, in't Zand and Heise 1998) are modulated
at time scales close to the orbital period. Folded light curves of the 1997 ASM
data and the 1999 PCA data are similar and show that the intensity increases at
periastron passages.Comment: To appear in The Astrophysical Journal (Letters
The Steady Spin Down Rate of 4U 1907+09
Using X-ray data from the Rossi X-Ray Timing Explorer (RXTE), we report the
pulse timing results of the accretion powered high mass X-ray binary (HMXRB)
pulsar 4U 1907+09 covering a time span of almost two years. We measured three
new pulse periods in addition to the previously measured four pulse periods. We
are able to connect pulse arrival times in phase for more than a year. The
source has been spinning down almost at a constant rate with a spin down rate
of
\dot \nu = (-3.54 \pm 0.02) \times 10^{-14} Hz s ^{-1} for more than
15 years. Residuals of pulse arrival times yield a very low level of random
walk noise strengths
\sim 2 \times 10^{-20} rad ^{2} sec ^{-3} on a time scale of 383 days, which
is four decades lower than that of the HMXRB pulsar Vela X-1. The noise
strength is only a factor of 5 greater than that of the low mass X-ray binary
pulsar (LMXRB) 4U 1626-67. The low level of the timing noise and the very
stable spin down rate of 4U 1907+09 makes this source unique among the HMXRBs,
providing another example, in addition to 4U 1626-67, of long term quiet spin
down from an accreting source. These examples show that the extended quiet spin
down episodes observed in the anomalous X-ray pulsars (AXPs) pulsars 1RXS
J170849.0-400910 and 1E 2259+586 do not necessarly imply that these sources are
not accreting pulsars.Comment: Submitted to MNRA
X-ray Flux Related Timing and Spectral Features of 2S 1417-62
RXTE observations of the X-ray transient pulsar 2S 1417-62 between 1999
November and 2000 August with a total exposure of ksec were
analyzed. Observations include a main outburst followed by a series of mini
outbursts. Changes in pulse morphology and pulse fraction were found to be
related to the changes in X-ray flux. Particularly low X-ray flux regions were
found to have significantly lower pulse fractions with different pulse
morphologies. The 3-60 keV PCA-HEXTE main outburst spectrum was modeled with an
absorbed power law model with high energy cut-off and a Gaussian Iron line
complex feature. Using the same spectral model, individual 3-20 keV PCA spectra
were found to be softer and less absorbed in low X-ray flux regions between
outbursts. Spectral studies showed that hydrogen column density was correlated,
and the power law index was anti-correlated with the 3-20 keV X-ray flux. X-ray
flux related spectral and timing features in 2S 1417-62 except for low X-ray
flux regions were interpreted as a sign of disc accretion with a similar
accretion geometry with a varying mass accretion rate (), whereas
spectral and timing features of the low X-ray flux regions were interpreted as
a sign of possible temporary accretion geometry change prior to the next
periastron where increases again to restore the original accretion
geometry.Comment: 14 pages, 6 figures, accepted for publication in MNRA
Low Frequency Flickering of TT Arietis:Hard and Soft X-ray Emission Region
Using archival ASCA observations of TT Arietis, X-ray energy spectra and
power spectra of the intensity time series are presented for the first time.
The energy spectra are well-fitted by a two continuum plasma emission model
with temperatures around 1 keV and 10 keV. A coherent feature at about 0.643
mHz appeared in the power spectra during the observation.Comment: 9 pages in PostScript including figures, accepted for publication in
Astrophysics and Space Science, available at
http://astroa.physics.metu.edu.tr/preprints.htm
Dense matter with eXTP
In this White Paper we present the potential of the Enhanced X-ray Timing and
Polarimetry (eXTP) mission for determining the nature of dense matter; neutron
star cores host an extreme density regime which cannot be replicated in a
terrestrial laboratory. The tightest statistical constraints on the dense
matter equation of state will come from pulse profile modelling of
accretion-powered pulsars, burst oscillation sources, and rotation-powered
pulsars. Additional constraints will derive from spin measurements, burst
spectra, and properties of the accretion flows in the vicinity of the neutron
star. Under development by an international Consortium led by the Institute of
High Energy Physics of the Chinese Academy of Science, the eXTP mission is
expected to be launched in the mid 2020s.Comment: Accepted for publication on Sci. China Phys. Mech. Astron. (2019
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