* Astronomy

Title: GRB 110205A: Anatomy of a long gamma-ray burst
Authors: B. Gendre (1), J.L. Atteia (2), M. Boër (3), F. Colas (4), A. Klotz (2), F. Kugel (5), M. Laas-Bourez (6), C. Rinner (5), J. Strajnic (7), G. Stratta (1), F. Vachier (4) ((1) ASDC, (2) Universite de Toulouse/IRAP, (3) OHP/CNRS, (4) IMCCE, (5) Observatory Chante-Perdrix, (6) UWA/ICRAR, (7) Lycee de l'Arc)

The Swift burst GRB 110205A was a very bright burst visible in the Northern hemisphere. GRB 110205A was intrinsically long and very energetic and it occurred in a low-density interstellar medium environment, leading to delayed afterglow emission and a clear temporal separation of the main emitting components: prompt emission, reverse shock, and forward shock. Our observations show several remarkable features of GRB 110205A : the detection of prompt optical emission strongly correlated with the BAT light curve, with no temporal lag between the two ; the detection of an X-ray excess above the extrapolation of the Band function measured in gamma-rays during the prompt phase ; and a large optical flare after the end of the prompt phase, that we interpret as a signature of the reverse shock. Beyond the pedagogical value offered by the excellent multi-wavelength coverage of a GRB with temporally separated radiating components, we discuss several questions raised by our observations: the nature of the prompt optical emission and the spectral evolution of the prompt emission at high-energies (from 0.5 keV to 150 keV) ; the origin of an x-ray flare at the beginning of the forward shock; and the modelling of the afterglow, including the reverse shock, in the framework of the classical fireball model.

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