* Astronomy

Title: The unusual X-ray light-curve of GRB 080307: the onset of the afterglow?
Authors: K.L. Page (1), R. Willingale (1), P.T. O'Brien (1), N.R. Tanvir (1), J.P. Osborne (1), B. Zhang (2), S.T. Holland (3,4), A.J. Levan (5), A. Melandri (6), R.L.C. Starling (1), D. Bersier (6), D.N. Burrows (7), J.E. Geach (8), P. Maxted (9) ((1) University of Leicester, (2) University of Nevada, (3) GSFC, (4) USRA, (5) University of Warwick, (6) Liverpool John Moores University, (7) PSU, (8) Durham University, (9) Keele University)

Swift-detected GRB 080307 showed an unusual smooth rise in its X-ray light-curve around 100 seconds after the burst, at the start of which the emission briefly softened. This `hump' has a longer duration than is normal for a flare at early times and does not demonstrate a typical flare profile. Using a two component power-law-to-exponential model, the rising emission can be modelled as the onset of the afterglow, something which is very rarely seen in Swift-X-ray light-curves. We cannot, however, rule out that the hump is a particularly slow early-time flare, or that it is caused by upscattered reverse shock electrons.

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