GRANAT / SIGMA Observation of the Early Afterglow from GRB 920723 in Soft Gamma - Rays
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چکیده
We present a GRANAT/SIGMA observation of the soft gamma-ray afterglow immediately after GRB 920723. The main burst is very bright. After ∼ 6 s, the burst light curve makes a smooth transition into an afterglow where flux decays as t −0.7. The power-law decay lasts for at least 1000 s; beyond this time, the afterglow emission is lost in the background fluctuations. At least ∼20% of main burst energy is emitted in the afterglow. At approximately ∼ 6 s after the trigger, we also observe an abrupt change in the burst spectrum. At t < 6 s, the ratio of 8–20 and 75–200 keV fluxes corresponds to the power law spectral index α = 0.0 − 0.3. At t = 6 s, the value of α increases to α ≈ 1 and stays at this level afterwards. The observed afterglow characteristics are discussed in connection with the relativistic fireball model of gamma-ray bursts.
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تاریخ انتشار 1999