Complex light-curve of the afterglow of GRB071010A

Abstract

We present and discuss the results of an extensive observational campaign devoted to GRB071010A, a long-duration gamma-ray burst detected by the Swift satellite. This event was followed for almost a month in the optical/near-infrared (NIR) with various telescopes starting from about 2min after the high-energy event. Swift -XRT observations started only later at about 0.4 d. The light-curve evolution allows us to single out an initial rising phase with a maximum at about 7min, possibly the afterglow onset in the context of the standard reball model, which is then followed by a smooth decay interrupted by a sharp rebrightening at about 0.6 d. The rebrightening was visible in both the optical/NIR and X-rays and can be interpreted as an episode of discrete energy injection, although various alternatives are possible. A steepening of the afterglow light curve is recorded at about 1 d. The entire evolution of the optical/NIR afterglow is consistent with being achromatic.