Abstract:
We present and discuss the results of an extensive observational campaign devoted to
GRB 071010A, 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 2 min 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 7 min, possibly the afterglow onset in the context of the standard
fireball 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. This could be one of the
few identified GRB afterglows with an achromatic break in the X-ray through the optical/NIR
bands. Polarimetry was also obtained at about 1 d, just after the rebrightening and almost
coincident with the steepening. This provided a fairly tight upper limit of 0.9 per cent for the
polarized-flux fraction.
