Issues in Gamma - Ray Bursts : Polarimetry and Dark Grbs
نویسندگان
چکیده
— We review some open problems in the physics of afterglows, namely their polarization properties and the existence of dark/faint bursts. Polarization studies yield precious insights in the physical structure and dynamical evolution of GRB jets, revealing their magnetization properties and their energy profile. Polari-metric observations of GRB 020813 already allowed to exclude a homogeneous jet for this event. We then present observations of faint/dark bursts, showing that some of them may be obscured by dust, while others are possibly just intrinsically dim. In 1999 the first successful detection of optical polarization from a gamma-ray burst (GRB) afterglow was obtained [1, 2]. Since then, several polarimetric measurements of GRB afterglows have been performed (see [3] and [4] for a review). Albeit being an observationally challenging task, the scientific community has shown wide interest in this field. Indeed, polarization has a high diagnostic power over a broad range of physical processes, from the emission mechanisms to the fireball structure and the properties of the close and far environment of the burst. The search for polarizion was driven by the hypothesis that the afterglow emission is due to synchrotron emission [5, 6, 7]. Its discovery, by itself, is now regarded as a strong evidence for this emission mechanism. For unresolved sources, like distant GRB c Società Italiana di Fisica
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