70 research outputs found
Luminosity-dependent spectral and timing properties of the accreting pulsar GX 304-1 measured with INTEGRAL
Context: Be/X-ray binaries show outbursts with peak luminosities up to a few
times erg/s, during which they can be observed and studied in
detail. Most (if not all) Be/X-ray binaries harbour accreting pulsars, whose
X-ray spectra in many cases contain cyclotron resonant scattering features
related to the magnetic field of the sources. Spectral variations as a function
of luminosity and of the rotational phase of the neutron star are observed in
many accreting pulsars. Aims: We explore X-ray spectral and timing properties
of the Be/X-ray binary GX 304-1 during an outburst episode. Specifically, we
investigate the behavior of the cyclotron resonant scattering feature, the
continuum spectral parameters, the pulse period, and the energy- and
luminosity-resolved pulse profiles. We combine the luminosity-resolved spectral
and timing analysis to probe the accretion geometry and the beaming patterns of
the rotating neutron star. Methods: We analyze the INTEGRAL data from the two
JEM-X modules, ISGRI and SPI, covering the January-February 2012 outburst,
divided in six observations. We obtain pulse profiles in two energy bands,
phase-averaged and phase-resolved spectra for each observation. Results: We
confirm the positive luminosity-dependence of the cyclotron line energy in GX
304-1, and report a dependence of the photon index on luminosity. Using a
pulse-phase connection technique, we find a pulse period solution valid for the
entire outburst. Our pulse-phase resolved analysis shows, that the centroid
energy of the cyclotron line is varying only slightly with pulse phase, while
other spectral parameters show more pronounced variations. Our results are
consistent with a scenario in which, as the pulsar rotates, we are exploring
only a small portion of its beam pattern.Comment: 12 pages, 12 figures, Accepted for publication in A&
Discovery and modelling of a flattening of the positive cyclotron line/luminosity relation in GX 304−1 with RXTE
The Rossi X-ray Timing Explorer (RXTE) observed four outbursts of the accreting X-ray binary transient source, GX 304−1 in 2010 and 2011. We present results of detailed 3–100 keV spectral analysis of 69 separate observations, and report a positive correlation between cyclotron line parameters, as well as other spectral parameters, with power-law flux. The cyclotron line energy, width and depth versus flux, and thus luminosity, correlations show a flattening of the relationships with increasing luminosity, which are well described by quasi-spherical or disc accretion that yield the surface magnetic field to be ∼5 × 10^(12) Gauss. Since HEXTE (High Energy X-ray Timing Experiment) cluster A was fixed aligned with the Proportional Counter Array field of view and cluster B was fixed viewing a background region 1°.5 off of the source direction during these observations near the end of the RXTE mission, the cluster A background was estimated from cluster B events using
HEXTEBACKEST.
This made possible the detection of the ∼55 keV cyclotron line and an accurate measurement of the continuum. Correlations of all spectral parameters with the primary 2–10 keV power-law flux reveal it to be the primary driver of the spectral shape. The accretion is found to be in the collisionless shock braking regime
XMM-EPIC observation of MCG-6-30-15: Direct evidence for the extraction of energy from aspinning black hole?
We present XMM-Newton European Photon Imaging Camera (EPIC) observations of
the bright Seyfert 1 galaxy MCG-6-30-15, focusing on the broad Fe K
line at ~6keV and the associated reflection continuum, which is believed to
originate from the inner accretion disk. We find these reflection features to
be extremely broad and red-shifted, indicating its origin from the very most
central regions of the accretion disk. It seems likely that we have caught this
source in the ``deep minimum'' state first observed by Iwasawa et al. (1996).
The implied central concentration of X-ray illumination is difficult to
understand in any pure accretion disk model. We suggest that we are witnessing
the extraction and dissipation of rotational energy from a spinning black hole
by magnetic fields connecting the black hole or plunging region to the disk.Comment: 6 pages and one postscript figure. Accepted for publication in MNRAS
letter
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