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Astron. Astrophys. Suppl. Ser. 138, 541-542

Images, light curves and spectra of GRB afterglow

J. Granot1 - T. Piran1,2 - R. Sari3

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

Received December 29, 1998; accepted June 9, 1999


We calculate the light curve and spectra near the peak and the self absorption break, for an adiabatic blast wave described by the Blandford-McKee solution, considering the emission from the whole region behind the shock front. The expected light curve and spectra are flat near the peak. This rules out the interpretation of the sharp peak observed in the optical afterglow of GRB 970508 as the expected peak of the light curve. The observed image of an afterglow is calculated for a broad range of frequencies. We show that for frequencies below the self absorption frequency the image is rather homogeneous, as opposed to the bright ring at the outer edge and dim center, which appear at higher frequencies. We fit the observed spectra of GRB 970508 to the detailed theory and obtain estimates of its physical parameters.

Key words: gamma-rays: bursts -- gamma-rays: theory -- magnetic fields -- hydrodynamics -- shock waves

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