1SUPERGIANT FAST X-RAY TRANSIENTS: A NEW CLASS OF HIGH MASS X-RAY BINARIES UNVEILED BY INTEGRAL

INTEGRAL monitoring of the Galactic Plane is revealing a growing number of recurrent X-ray transients, charac-terised by short outbursts with very fast rise times ( ∼ tens of minutes) and typical durations of a few hours. Here we show that several of these transients are associated with OB supergiants and hence define a new class of massive X-ray binaries which we call Supergiant Fast X-ray Tran-sients. Many other transient X-ray sources display sim-ilar X-ray characteristics, suggesting that they belong to the same class. Since they are difficult to detect and their number is growing fast and steadily, they could represent a major class of X-ray binaries