Black Hole Accretion in Transient X-Ray Binaries

Abstract

Recent work on the modes of accretion onto black holes (BHs) in Soft X-Ray Transients (SXTs) is reviewed, with an emphasis on uncertainties affecting models of accretion during quiescence (inner hot flow, outer thin disk). Various interpretations of the quiescent X-ray luminosity difference between systems containing neutron stars (NSs) and systems containing BH candidates are also summarized. A new scenario, which does not require BH candidates to possess an event horizon, is presented here. This scenario may be ruled out in the future, from detailed X-ray spectroscopic diagnostics or from the absence of type I X-ray bursts in systems containing BH candidates.