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X-Ray Variation Statistics and Wind Clumping in Vela X-1
- Publication Year :
- 2010
- Publisher :
- United States: NASA Center for Aerospace Information (CASI), 2010.
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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. Accreted clump masses derived from the INTEGRAL data are on the order of 5 x 10(exp 19)-10(exp 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.
- Subjects :
- Astrophysics
Subjects
Details
- Language :
- English
- Database :
- NASA Technical Reports
- Notes :
- DLR 50 OR 0808, , ITN 215212, , NNG06EO90A
- Publication Type :
- Report
- Accession number :
- edsnas.20100024533
- Document Type :
- Report