The clumpy absorber in the high-mass X-ray binary Vela X-1

Abstract

Bright and eclipsing, the high-mass X-ray binary Vela X-1 offers a unique opportunity to study accretion onto a neutron star from clumpy winds of O/B stars and to disentangle the complex accretion geometry of these systems. In Chandra-HETGS spectroscopy at orbital phase ~0.25, when our line of sight towards the source does not pass through the large-scale accretion structure such as the accretion wake, we observe changes in overall spectral shape on timescales of a few kiloseconds. This spectral variability is, at least in part, caused by changes in overall absorption and we show that such strongly variable absorption cannot be caused by unperturbed clumpy winds of O/B stars. We detect line features from high and low ionization species of silicon, magnesium and neon whose strengths and presence depend on the overall level of absorption. They imply a co-existence of cool and hot gas phases in the system that we interpret as a highly variable, structured accretion flow close to the compact object such as has been recently seen in simulations of wind accretion in high-mass X-ray binaries.

17 pages, 14 figures; A&A accepted

References in corpus (17)

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Cited by in corpus (6)

• Chandra reveals a possible ultra-fast outflow in the super-Eddington Be/X-ray binary Swift J0243.6+6124
• Chandra X-ray spectroscopy of the focused wind in the Cygnus X-1 system III. Dipping in the low/hard state
• A Comprehensive Chandra Study of the Disk Wind in the Black Hole Candidate 4U 1630-472
• High-resolution X-ray spectroscopy of the stellar wind in Vela X-1 during a flare
• Spectral evidence of an accretion disk in wind-fed X-ray pulsar Vela X-1 during an unusual spin-up period
• Variability in high-mass X-ray binaries