Accounting for the XRT early steep decay in models of the prompt GRB emission

Abstract

The Swift-XRT observations of the early X-ray afterglow of GRBs show that it usually begins with a steep decay phase. A possible origin of this early steep decay is the high latitude emission that subsists when the on-axis emission of the last dissipating regions in the relativistic outflow has been switched-off. We wish to establish which of various models of the prompt emission are compatible with this interpretation. We successively consider internal shocks, photospheric emission, and magnetic reconnection and obtain the typical decay timescale at the end of the prompt phase in each case. Only internal shocks naturally predict a decay timescale comparable to the burst duration, as required to explain XRT observations in terms of high latitude emission. The decay timescale of the high latitude emission is much too short in photospheric models and the observed decay must then correspond to an effective and generic behavior of the central engine. Reconnection models require some ad hoc assumptions to agree with the data, which will have to be validated when a better description of the reconnection process becomes available.

4 pages, 2 figures

References in corpus (8)

• The Internal-Collision-Induced Magnetic Reconnection and Turbulence (ICMART) Model of Gamma-Ray Bursts
• Prompt GRB emission from gradual energy dissipation
• Temporal Evolution Of Thermal Emission From Relativistically Expanding Plasma
• A comprehensive analysis of Swift/XRT data: I. Apparent spectral evolution of GRB X-ray tails
• X-ray Hardness Evolution in GRB Afterglows and Flares: Late Time GRB Activity Without N_H Variations
• A new model for infrared and submillimetre counts
• Did Swift measure GRB prompt emission radii?
• The full curvature effect expected in early X-ray afterglow emission of gamma-ray bursts

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