出版社：SISSA, Scuola Internazionale Superiore di Studi Avanzati
摘要：Galactic black hole transients (GBHTs) spend most of their time in the low/hard spectral state
during the outburst decay. This state exhibits a hard X-ray spectrum, with X-ray flux correlating
with the radio and sometimes the optical/infrared flux. The radio and some part of the infrared
emission comes from a compact jet. Understanding the interplay between X-ray emission and
jet properties is very important in understanding the accretion geometry in the hard state. As the
luminosity declines, the spectra of the GBHTs get harder. However, for a few sources at very low
luminosity levels a softening of the spectrum has been observed. In this work, our motivation
is to discuss the evolution of GBHTs at the very lowest luminosity levels using RXTE data and
compare with evolution of the radio and the optical/infrared fluxes. We discuss the possible
reasons for softening and whether the softening is related to the jet emission.
