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

Thumbnail Image

Files

aa13981-09.pdf (337.85 KB)

Links to Files

https://www.aanda.org/articles/aa/full_html/2010/11/aa13981-09/aa13981-09.html

Permanent Link

https://doi.org/10.1051/0004-6361/200913981
 http://hdl.handle.net/11603/29887

Collections

UMBC Center for Space Sciences and Technology (CSST) / Center for Research and Exploration in Space Sciences & Technology II (CRSST II)
UMBC Faculty Collection
UMBC Physics Department

Author/Creator

Author/Creator ORCID

https://orcid.org/0000-0002-4656-6881

Date

2010-09-09

Type of Work

journal articles
Text

Department

Program

Citation of Original Publication

Fürst, F., I. Kreykenbohm, K. Pottschmidt, J. Wilms, M. Hanke, R. E. Rothschild, P. Kretschmar, et al. “X-Ray Variation Statistics and Wind Clumping in Vela X-1.” Astronomy & Astrophysics 519 (September 1, 2010): A37. https://doi.org/10.1051/0004-6361/200913981.

Rights

This item is likely protected under Title 17 of the U.S. Copyright Law. Unless on a Creative Commons license, for uses protected by Copyright Law, contact the copyright holder or the author.
Attribution 4.0 International (CC BY 4.0)

Subjects

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 s, 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 NH. Accreted clump masses derived from the INTEGRAL data are on the order of 5 x 10¹⁹ - 10²¹ 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.