The recent discovery of a new class of recurrent and fast X-ray transient sources, the Supergiant Fast X-ray Transients, poses interesting questions on the possible mechanisms responsible for their transient X-ray emission. The association with blue supergiants, the spectral properties similar to those of accreting pulsars and the detection, in a few cases, of X-ray pulsations, confirm that these transients are High Mass X-ray Binaries. Their transient behaviour is quite surprising since neutron stars accreting from the winds of supergiant companions were seen as persistent sources. I review the different mechanisms proposed to explain their transient outbursts and the link to the persistent sources.
37th COSPAR Scientific Assembly
- Pub Date:
- Invited talk at the 37th COSPAR Scientific Assembly, held on 13-20 July 2008, in Montreal, Canada. Symposium E, session 11. Accepted for publication in Advances in Space Research. The text and the title have been modified according to the referee's suggestions