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Astron. Astrophys. Suppl. Ser.
Volume 138, Number 3, September 1999
Gamma-Ray Bursts in the Afterglow Era Contents Rome, November 3-6, 1998
Page(s) 537 - 538
Published online 15 September 1999
DOI: 10.1051/aas:1999342

Astron. Astrophys. Suppl. Ser. 138, 537-538

The early afterglow

R. Sari1 and T. Piran 2

1 - Theoretical Astrophysics, California Institute of Technology, Pasadena, CA 91125, U.S.A.
2 - Racah Institute of Physics, The Hebrew University, Jerusalem 91904, Israel , and Department of Physics, Columbia University, New York, NY 10027, U.S.A.

Received December 29; accepted December 29, 1998


We calculate the expected spectrum and light curves of the early afterglow. For short GRBs the peak of the afterglow will be delayed, typically, by few dozens of seconds after the burst. The X-ray and $\gamma$-ray characteristics of this delayed emission provide a way to discriminate between late internal shocks emission (part of the GRB) and the early afterglow signal. Detection of this delayed emission will prove the internal shock scenario as producing the GRB, and will pinpoint the initial Lorentz factor $\gamma_0$. In the optical band, the dominant emission arises from the reverse shock. This shock, carries a comparable amount of energy to the forward shock. It radiates this energy at much lower frequencies, producing a short optical flash of 15th magnitude or brighter.

Copyright The European Southern Observatory (ESO)

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