X-ray variability of GX 339 - 4 in its very high state

Abstract

Results are presented on observations of GX 339 - 4 performed with the large-area counters aboard Ginga when this X-ray source was in its very high state. It its shown that the X-ray energy spectrum of GX 339 - 4 consists of a low-energy component, interpreted as being due to the disk blackbody radiation, and a high-energy tail (the Comptonized blackbody component). On time scales less than several minutes, the X-rays displayed rapid time variations, interpreted as being due to the Comptonized blackbody component. On time scales greater than hours, the disk blackbody component and the Comptonized blackbody component changed independently. These changes, however, took place within some restricted regions in the X-ray hardness-ratio-intensity diagrams: a hardness ratio increasing (with the X-ray flux) branch, a hardness ratio decreasing branch, and their crossing region.