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The GRB early optical flashes from internal shocks: application to GRB990123, GRB041219a and GRB060111b

Research paper by D. M. Wei

Indexed on: 08 Oct '06Published on: 08 Oct '06Published in: Astrophysics



Abstract

With the successful launch of the Swift Gamma-Ray Burst Explorer, people expected the prompt optical flash like GRB990123 would be easily detected. However the fact that early optical flash have not been detected for a number of GRBs indicates the reverse shock must be suppressed. Here we explore the possibility that the optical flash may arise from the internal shock. We find that, under certain circumstance, the optical flash of GRB990123 and GRB060111b can really be explained by the internal shock. For GRB041219a, the prompt optical emission was correlated with the gamma-ray emission, we explain this feature also in the internal shock scenario, the optical emission is the low energy extension of the gamma-ray emission, and we can restrict its redshift $z\sim 0.2$. As for GRB050904, we have shown in previous paper that the optical flash was produced by synchrotron radiation and the X-ray flare was produced by the synchrotron-self-Compton mechanism. Therefore we conclude that the early optical flash of GRBs can usually come from the internal shock. Meanwhile since the condition to produce the optical flash is not easily satisfied, so the optical flash like GRB990123 should not be common in GRBs. In addition, we also discussed the synchrotron-self-Compton effect in the internal shock model, and find that for different values of parameters, there would be soft gamma-ray (100 KeV), hard gamma-ray (10 MeV) and GeV flare accompanying the optical flash. For GRB like GRB990123, a GeV flare with fluence about 10^{-8} erg cm^{-2} s^{-1} is expected, which may be detected by the GLAST satellite.