The complex light-curve of the afterglow of GRB071010A

TL;DR

This paper presents a detailed multi-wavelength observational analysis of GRB071010A, revealing an initial afterglow onset, a rebrightening episode likely due to energy injection, and an achromatic break, with polarimetry providing constraints on magnetic field structure.

Contribution

It provides one of the few detailed optical/NIR and X-ray light curves showing an achromatic break and rebrightening in a GRB afterglow, with polarimetry constraints.

Findings

Initial afterglow onset at about 7 minutes

Rebrightening at about 0.6 days consistent with energy injection

Achromatic break observed around 1 day

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 0.4d. 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 fireball model, which is then followed by a smooth decay interrupted by a sharp rebrightening at about 0.6d. 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 1d. 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 1d, just after the rebrightening and almost coincident with the steepening. This provided a fairly tight upper limit of 0.9% for the polarized-flux fraction.