Unveiling Supergiant Fast X‐Ray Transient Sources with<i>INTEGRAL</i>

Abstract

Supergiant high-mass X-ray binaries (SGXBs) are believed to be rare objects, as stars in the supergiant phase have a very short lifetime and to date only about a dozen of them have been discovered. They are known to be persistent and bright X-ray sources. INTEGRAL is changing this classical picture, as its observations are revealing the presence of a new subclass of SGXBs that have been labeled supergiant fast X-ray transients (SFXTs), since they are strongly characterized by fast X-ray outbursts lasting less than a day, typically a few hours. We report on IBIS detections of newly discovered fast X-ray outbursts from 10 sources, four of which have been recently optically identified as supergiant high-mass X-ray binaries. For one of them in particular, IGR J112155952, we observe fast X-ray transient behavior for the first time. The remaining six sources ( IGR J164794514, IGR J164184532, IGR J16195 4945=AX J1619294945, XTE J1743363, AX J1749.12733, and IGR J174072808) are still unclassified; however, they can be considered candidate SFXTs because of their similarity to the known SFXTs.