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[80.04] Broadband Spectral Analysis of a Gamma-Ray Burst with a Possible Thermal Component

Y. Kaneko, R.D. Preece, M.S. Briggs (University of Alabama in Huntsville / NSSTC)

In the early phase of fireball shock model of gamma-ray burst (GRB) prompt emission, a thermal spectral component should be expected due to the expanding, optically-thick fireball. Several GRBs that display exceptionally hard spectral behavior at lower energies have been reported in the past, some of which can be adequately fitted with the thermal blackbody model at the beginning of the bursts. The thermal component, if real, could provide strong constraints on the expanding fireball and thus, on the prompt emission mechanism and the source environment. At least one such burst (GRB970111) was observed with both BATSE and Bepposax WFC, providing a broad energy coverage of 2 - 2000 keV. The recent work by Ghirlanda et al. (2003) using BATSE data alone as well as the preliminary result of our BATSE-BeppoSAX joint analysis suggest existence of blackbody component with temperature ~ 40 - 70 keV in the first ~ 5 seconds of this burst. In this work, we present detailed broadband spectral analysis results of the possible thermal component of GRB970111, and associated characteristics of the relativistically expanding fireball.

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Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.