Picture of the Month
INTEGRAL observes fast X-ray transients with supergiant companions
INTEGRAL monitoring of the Galactic Plane has revealed a number of recurrent transients wich are characterized by short outbursts (a few hours) with very fast rise times (tens of minutes). Several of these transients have an OB supergiant star as companion. About a dozen of these systems were known before the launch of INTEGRAL and they were assumed to be really scarce.
However, INTEGRAL observations show that most of the new sources are highly absorbed which makes them very hard to detect at (softer) X-ray energies. The detection of several of these sources at hard X-ray energies suggests the presence of a much larger class of sources: Supergiant X-ray Binaries. Apart from the sensitivity at hard X-ray energies the long observations and monitoring of the Galactic Plane by INTEGRAL contributes to the likelihood of catching these systems in an outburst.
The X-ray characteristics originate from mass transfer which is affected substantially by the strong stellar winds (with high density variations) surrounding supergiants onto the compact object.
A paper by Negueruela et al. describing the results is in press (astro-ph/0511088).
The figure shows an artist's impression of the stellar wind and mass transfer around a supergiant with a light curve observed with IBIS onboard INTEGRAL overlayed.
Credits: I. Negueruela (University of Alicante, Spain) and artist's impression C. Carreau (ESA).
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