A Sequence of Declining Outbursts from GX 339–4

The flux and spectrum of the black hole candidate GX 339-4 has been monitored by the Burst and Transient Source Experiment (BATSE) on the Compton Gamma-Ray Observatory since the observatory became operational in 1991 May. Between the summer of 1991 and the fall of 1996, eight outbursts from GX 339-4 were observed. The history of these outbursts is one of declining fluence or total energy release, as well as a shortening of the time between outbursts. A rough linear correlation exists between the fluence emitted during an outburst and the time elapsed between the end of the previous outburst and the beginning of the current one. The peak flux is also roughly linearly correlated with outburst fluence. The light curves of the earlier, more intense, outbursts (except for the second one) can be modeled by a fast exponential (time constant ~10 days) followed by a slower exponential (~100 days) on the rise and a fast exponential decay (~5 days) on the fall. The later, weaker, outbursts are modeled with a single, rising time constant (~20 days) and a longer decay on the fall (~50 days). An exponential model gives a marginally better fit than a power law to the rise/decay profiles. GX 339-4 is a unique source in having more frequent outbursts than other low-mass X-ray binary black hole candidates. These observations can be used to constrain models of the behavior of the accretion disk surrounding the compact object.