出版社：SISSA, Scuola Internazionale Superiore di Studi Avanzati
摘要：Recent observations of two black hole candidates (GX 339-4 and J1753.5-0127) in the low-hard
state (LX/LEdd ≃ 0.003 − 0.05) suggest the presence of a cool accretion disk very close to the
innermost stable orbit of the black hole. This runs counter to models of the low-hard state in
which the cool disk is truncated at a much larger radius. We study the interaction between a
moderately truncated disk and a hot inner flow. Ion-bombardment heats the surface of the disk in
the overlap region between a two-temperature advection-dominated accretion flow and a standard
accretion disk, producing a hot (kTe ≃ 70keV) layer on the surface of the cool disk. The hard
X-ray flux from this layer heats the inner parts of the underlying cool disk, producing a soft X-ray
excess. Together with interstellar absorption these effects mimic the thermal spectrum from a disk
extending to the last stable orbit. The results show that soft excesses in the low-hard state are a
natural feature of truncated disk models.
