17 research outputs found
On the nature of the variability power decay towards soft spectral states in X-ray binaries. Case study in Cyg X-1
A characteristic feature of the Fourier Power Density Spectrum (PDS) observed
from black hole X-ray binaries in low/hard and intermediate spectral states is
a broad band-limited noise, characterized by a constant below some frequency (a
``break'' frequency) and a power law above this frequency. It has been shown
that the variability of this type can be produced by the inward diffusion of
the local driving perturbations in a bounded configuration (accretion disk or
corona). In the framework of this model, the perturbation diffusion time t_0 is
related to the phenomenological break frequency, while the PDS power-law slope
above the ``break'' is determined by the viscosity distribution over the
configuration. he perturbation diffusion scenario explains the decay of the
power of X-ray variability observed in a number of compact sources (containing
black hole and neutron star) during an evolution of theses sources from
low/hard to high/soft states. We compare the model predictions with the subset
of data from Cyg X-1 collected by the Rossi X-ray Time Explorer (RXTE). Our
extensive analysis of the Cyg X-1 PDSs demonstrates that the observed
integrated power P_x decreases approximately as a square root of the
characteristic frequency of the driving oscillations \nu_{dr}. The RXTE
observations of Cyg X-1 allow us to infer P_{dr} and t_0 as a function of
\nu_{dr}. Using the inferred dependences of the integrated power of the driving
oscillations P_{dr} and t_0 on \nu_{dr} we demonstrate that the power predicted
by the model also decays as P_{x,diff} proportional to \nu_{dr}^{-0.5} that is
similar to the observed P_{x} behavior.Comment: 15 page, 5 figures, accepted for publication in the Astrophysical
Journa
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
Infrared identification of 4U1323-619 revisited
We re-examine the infrared counterpart of the dipping low-mass x-ray binary
4U1323-619. New X-ray data available from the XMM and Chandra observatories
combined with archival IR observations from the ESO 3.6m New Technology
Telescope allow us to define a new possible counterpart. We present here its
photometric properties and compare them with a simple analytical model of an
accretion disc illuminated by the hot central corona known to be present in the
binary system.Comment: 4 pages, 1 table, 1 figure, accepted to MNRAS Letter