Spectral study of GX339‐4 in the low intensity state observed with GINGA

Abstract

Energy spectra of the black hole candidate GX339‐4 in the low intensity state were observed on four occasions through 1989 to 1991 with the Large Area Counters onboard the GINGA satellite. The spectra showed significant deviations from a power‐law, with an iron Kα emission line at ∼6.4 keV and broad iron K‐edge structure above ∼7 keV. The energy spectra above 4 keV were successfully explained with a reflection model, in which a part of the incident x‐rays with a power‐law spectrum is Compton reflected by optically thick matter. The line equivalent width with respect to the reflection component decreases as the source flux increases, consistent with an increase in the ionization state of the material so that resonant absorption followed by Auger ionization depletes the line.