Batse Soft Gamma-ray Observations of Groj0422+32

We report results of a comprehensive study of the soft gamma-ray (30 keV to 1.7 MeV) emission of GROJ0422+32 during its first known outburst in 1992. These results were derived from the BATSE earth-occultation database with the JPL data analysis package, EBOP (Enhanced BATSE Occultation Package). Results presented here focus primarily on the long-term temporal and spectral variability of the source emission associated with the outburst, which complement those reported earlier by BATSE (Harmon et al. 1993, Ling et al. 2000), OSSE (Grove et al. 1998), COMPTEL (Van Dijk et al. 1995) and SIGMA (Sunyaev et al. 1993; Roques et al. 1994). The light curves with 1-day resolution in six broad energy-bands (e.g. 35-100 keV, 100-200 keV, 200-300 keV, 300-400 keV, 400-700 keV and 700-1000 keV) show the high-energy flux (>200 keV) led the low-energy flux (<200 keV) by ∼ 5 days in reaching the primary peak, but lagged the latter by ∼ 7 days in starting the declining phase. We confirm the ”secondary maximum” of the lowenergy (<200 keV) flux at ∼TJD 8970-8981, ∼ 120 days after the first maximum, reported earlier by the BATSE team (Harmon et al. 1993). Our data show that the ”secondary maximum” was also prominent in the 200-300 keV band, but became less pronounced at higher energies. During this 200-day period, the spectrum evolved from a power-law with photon index of 1.75 on TJD 8839, to a shape that can be described by a Comptonized model or an exponential power law below 300 keV, with a variable power-law tail above 300 keV. The spectrum remained roughly in this two-component shape until ∼ 9 November (TJD 8935) when the 35-429 keV luminosity dropped to below ∼ 20% of its peak value observed on TJD-8848. It then returned to the initial power-law shape with an index of ∼ 2 and stayed in this shape until the end