Spectral Lags of Gamma-Ray Bursts From Ginga and BATSE
Abstract
The analysis of spectral lag between energy bands, which combines temporal and spectral analyses, can add strict constraints to gamma-ray burst (GRB) models. In previous studies, the lag analysis focused on the lags between channel 1 (25-57 keV) and channel 3 (115-320 keV) from the Burst and Transient Source Experiment (BATSE). In this paper, we analyzed the cross-correlation average lags (including confidence regions) between energy bands for two GRB samples: 19 events detected by Ginga, and 109 bright events detected by BATSE. We paid special attention to the BATSE GRBs with known redshifts, because there has been a reported connection between lag and luminosity. The use of Ginga extends our knowledge of spectral lags to lower energy (~2 keV). We found that lags between energy bands are small. The lag between the peak of ~40 keV photons and ~200 keV photons is ~0.08 sec. The upper limit of the lag between \~7 keV photons and ~70 keV photons is ~0.5 sec. Thus, there are not large shifts at low energy. We found that about 20% of GRBs have detectable lags between energy bands both from Ginga and BATSE samples. Our results imply that, in the context of the internal shock model, the burst radiation process must vary as the reverse shock moves through the shell.Keywords
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