HETE-2 localization and observation of the gamma-ray burst GRB 020813

A bright, long gamma-ray burst (GRB) was detected and localized by the instruments on board the High Energy Transient Explorer 2 satellite (HETE-2) at 02:44:19.17 UTC (9859.17s UT) on 2002 August 13. The location was reported to the GRB Coordinates Network (GCN) about 4min after the burst. In the prompt emission, the burst had a duration of approximately 125s, and more than four peaks. We analyzed the time-resolved 2–400keV energy spectra of the prompt emission of GRB 020813 using the Wide Field X-Ray Monitor (WXM) and the French Gamma Telescope (FREGATE) in detail. We found that the early part of the burst (17–52s after the burst trigger) shows a depletion of low-energy photons below about 50keV. It is difficult to explain the depletion by either synchrotron self-absorption or Comptonization. One possibility is that the low-energy depletion may be understood as a mixture of “jitter” radiation with the usual synchrotron radiation component.

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