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).
