Illustration of a Supergiant Fast X-ray Transient (SFXT) source
This artist's impression shows a high-mass binary system, composed of a supergiant luminous star (in blue) and a compact stellar object, such as a neutron star.
As discovered by ESA's INTEGRAL observatory, many of these supergiant systems produce strong and exceptionally fast-rising X-ray outbursts lasting a few hours only, hence their name 'supergiant fast X-ray transients'.
The outbursts may depend on the way stellar material is exchanged between the supergiant star and the compact object.
The light curve at the bottom-right was retrieved by INTEGRAL from the supergiant fast X-ray transient source IGR J17544-2619 on 17 September 2003.
The curve shows a very fast X-ray outburst from the compact object, lasting about two hours only, with very fast rise and slow decay. The counterpart of this source is a luminous supergiant, unambiguously identified by ESA's XMM-Newton and NASA's Chandra X-ray observatories.