AAS 201st Meeting, January, 2003
Session 84. Gamma Ray Observations
Poster, Wednesday, January 8, 2003, 9:20am-6:30pm, Exhibit Hall AB

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[84.03] Calorimetry of GRB afterglows -- a Direct Measure of the Fireball Energy

E. Berger, S.R. Kulkarni (Caltech), D.A. Frail (NRAO)

Radio observations of GRB afterglows allow us to trace the evolution of the afterglow to late times (t>1 year). As such, these observations directly measure the transition to non-relativistic velocities and the subsequent evolution. In this regime, we can use the simple Sedov-Taylor formulation to perform a direct calorimetry of the fireball, which is independent of geometric effects (i.e. beaming). Moreover, the early radio observations provide a direct measure of the size of the fireball via Interstellar Scintillation. This measurement is then combined with the non-relativistic evolution to provide an even more robust estimate of the fireball energy. In this talk I will demonstrate the unique advantage that this method provides over other estimates (e.g. using broad-band modeling), and I will place the energy measurements in the context of past results.

The author(s) of this abstract have provided an email address for comments about the abstract: ejb@astro.caltech.edu

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