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arXiv · 1005.5243

X-ray variation statistics and wind clumping in Vela X-1

Felix Fürst·Ingo Kreykenbohm·Katja Pottschmidt·Jörn Wilms·Manfred Hanke·Richard E. Rothschild·Peter Kretschmar·Norbert S. Schulz·David P. Huenemoerder·Dmitry Klochkov·Rüdiger Staubert
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Abstract

We investigate the structure of the wind in the neutron star X-ray binary system Vela X-1 by analyzing its flaring behavior. Vela X-1 shows constant flaring, with some flares reaching fluxes of more than 3.0 Crab between 20-60 keV for several 100 seconds, while the average flux is around 250 mCrab. We analyzed all archival INTEGRAL data, calculating the brightness distribution in the 20-60 keV band, which, as we show, closely follows a log-normal distribution. Orbital resolved analysis shows that the structure is strongly variable, explainable by shocks and a fluctuating accretion wake. Analysis of RXTE ASM data suggests a strong orbital change of N_H. Accreted clump masses derived from the INTEGRAL data are on the order of 5 x 10^19 -10^21 g. We show that the lightcurve can be described with a model of multiplicative random numbers. In the course of the simulation we calculate the power spectral density of the system in the 20-100 keV energy band and show that it follows a red-noise power law. We suggest that a mixture of a clumpy wind, shocks, and turbulence can explain the measured mass distribution. As the recently discovered class of supergiant fast X-ray transients (SFXT) seems to show the same parameters for the wind, the link between persistent HMXB like Vela X-1 and SFXT is further strengthened.

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Felix Fürst, Ingo Kreykenbohm, Katja Pottschmidt, Jörn Wilms, Manfred Hanke, Richard E. Rothschild, Peter Kretschmar, Norbert S. Schulz, David P. Huenemoerder, Dmitry Klochkov, Rüdiger Staubert. 2010-05-28. X-ray variation statistics and wind clumping in Vela X-1. https://doi.org/10.1051/0004-6361/200913981

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