Supergiant 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, characterised 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 Transients (SFXTs). Many other transient X-ray sources display similar 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. 
Ignacio Negueruela (Alicante), David M. Smith (UC Santa Cruz), Pablo   Reig (Crete), Sylvain Chaty (CEA/Saclay & Paris 7), J...