75 research outputs found
Long-term pulse profile study of the Be/X-ray pulsar SAX J2103.5+4545
Aims. We present the first long-term pulse profile study of the X-ray pulsar
SAX J2103.5+4545. Our main goal is to study the pulse shape correlation either
with luminosity, time or energy.
Methods. This Be/X-ray binary system was observed from 1999 to 2004 by RXTE
PCA, and by INTEGRAL from 2002 to 2005, during the Performance and Verification
(PV) phase and the Galactic Plane Scan survey (GPS). X-ray pulse profiles were
obtained in different energy ranges. The long-term spectral variability of this
source is studied. The long-term flux, frequency and spin-up rate histories are
computed. A new set of orbital parameters are also determined.
Results. The pulse shape is complex and highly variable either with time or
luminosity. However, an energy dependence pattern was found. Single, double,
triple or even quadruple peaks pulse profile structure was obtained. It was
confirmed that SAX J2103.5+4545 becomes harder when the flux is higher. The new
orbital solution obtained is: P_orb= 12.66528+-0.00051 days, e = 0.401+-0.018,
w = 241.36+-2.18 and a_xsin i = 80.81+-0.67 lt-s.Comment: 9 pages, 11 figures, submitted to Astronomy & Astrophysic
Orbital Decay and Evidence of Disk Formation in the X-ray Binary Pulsar OAO 1657-415
OAO 1657-415 is an eclipsing X-ray binary wind-fed pulsar that has exhibited
smooth spin-up/spin-down episodes and has undergone several torque reversals
throughout its long history of observation. We present a frequency history
spanning nearly 19 years of observations from the Burst and Transient Source
Experiment (CGRO/BATSE) and from the Gamma-Ray Burst Monitor (Fermi/GBM). The
analysis suggests two modes of accretion: one resulting in steady spin-up
during which we believe a stable accretion disk is present and one that results
in what appears to be a random walk in spin frequency where an unstable
accretion disk forms alternating in direction ("flip flop"). Orbital elements
of the pulsar system are determined at several intervals throughout this
history. With these ephemerides, statistically significant orbital decay
() is established
suggesting a transition between wind-fed and disk-mediated accretion
4U 1626-67 as seen by Suzaku before and after the 2008 torque reversal
Aims. The accretion-powered pulsar 4U 1626-67 experienced a new torque
reversal at the beginning of 2008, after about 18 years of steadily spinning
down. The main goal of the present work is to study this recent torque reversal
that occurred in 2008 February.
Methods. We present a spectral analysis of this source using two pointed
observations performed by Suzaku in 2006 March and in 2010 September.
Results. We confirm with Suzaku the presence of a strong emission-line
complex centered on 1 keV, with the strongest line being the hydrogen-like Ne
Ly-alpha at 1.025(3) keV. We were able to resolve this complex with up to seven
emission lines. A dramatic increase of the intensity of the Ne Ly-alpha line
after the 2008 torque reversal occurred, with the equivalent width of this line
reaching almost the same value measured by ASCA in 1993. We also report on the
detection of a cyclotron line feature centered at ~37 keV. In spite of the fact
that an increase of the X-ray luminosity (0.5-100 keV) of a factor of ~2.8
occurred between these two observations, no significant change in the energy of
the cyclotron line feature was observed. However, the intensity of the ~1 keV
line complex increased by an overall factor of ~8.
Conclusions. Our results favor a scenario in which the neutron star in 4U
1626-67 accretes material from a geometrically thin disk during both the
spin-up and spin-down phases.Comment: 7 pages, 5 figures and 2 tables. Accepted in A&
Earth Occultation Imaging of the Low Energy Gamma-Ray Sky with GBM
The Earth Occultation Technique (EOT) has been applied to Fermi's Gamma-ray
Burst Monitor (GBM) to perform all-sky monitoring for a predetermined catalog
of hard X-ray/soft gamma-ray sources. In order to search for sources not in the
catalog, thus completing the catalog and reducing a source of systematic error
in EOT, an imaging method has been developed -- Imaging with a Differential
filter using the Earth Occultation Method (IDEOM). IDEOM is a tomographic
imaging method that takes advantage of the orbital precession of the Fermi
satellite. Using IDEOM, all-sky reconstructions have been generated for ~sim 4
years of GBM data in the 12-50 keV, 50-100 keV and 100-300 keV energy bands in
search of sources otherwise unmodeled by the GBM occultation analysis. IDEOM
analysis resulted in the detection of 57 sources in the 12-50 keV energy band,
23 sources in the 50-100 keV energy band, and 7 sources in the 100-300 keV
energy band. Seventeen sources were not present in the original GBM-EOT catalog
and have now been added. We also present the first joined averaged spectra for
four persistent sources detected by GBM using EOT and by the Large Area
Telescope (LAT) on Fermi: NGC 1275, 3C 273, Cen A, and the Crab
The pre-outburst flare of the A 0535+26 August/September 2005 outburst
We study the spectral and temporal behavior of the High Mass X-ray Binary A
0535+26 during a `pre-outburst flare' which took place ~5 d before the peak of
a normal (type I) outburst in August/September 2005. We compare the studied
behavior with that observed during the outburst. We analyse RXTE observations
that monitored A 0535+26 during the outburst. We complete spectral and timing
analyses of the data. We study the evolution of the pulse period, present
energy-dependent pulse profiles both at the initial pre-outburst flare and
close to outburst maximum, and measure how the cyclotron resonance-scattering
feature (hereafter CRSF) evolves. We present three main results: a constant
period P=103.3960(5)s is measured until periastron passage, followed by a
spin-up with a decreasing period derivative of Pdot=(-1.69+/-0.04)x10^(-8)s/s
at MJD 53618, and P remains constant again at the end of the main outburst. The
spin-up provides evidence for the existence of an accretion disk during the
normal outburst. We measure a CRSF energy of Ecyc~50kev during the pre-outburst
flare, and Ecyc~46kev during the main outburst. The pulse shape, which varies
significantly during both pre-outburst flare and main outburst, evolves
strongly with photon energy.Comment: 4 pages, 4 figures, accepted for publication in A&A Letters. To be
published in parallel to Postnov et al. 200
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