1209.4393 (Mohammad A. F. Basha)

Two distinct phases in the first 13 seconds of GRB110731a prompt emission    [PDF]

Mohammad A. F. Basha

In this work, the time-resolved BAT/GBM/LAT joint spectral analysis of GRB110731A during the prompt phase from GBM trigger and up to 13 seconds showed that, at the very early phase of prompt emission, the emission mechanism is the closest to the standard fireball model which over-predicts the thermal photospheric emission and used to contradict observations. Lightcurves at different energy bands revealed two distinguishable phases that may be from different regions, an early phase, which is not detected by LAT, is dominated by lower energies, which arises from the photospheric emissions without any emissions involved from dissipation mechanisms and characterized by low Lorentz factor and high radiation efficiency, this is followed by a later phase having more complex structure that remarkably follow the same track in all energy bands and is attributed to emissions from internal shocks. This burst is a good candidate to study both thermal and non-thermal emissions since the two phases can be clearly separated in lightcurve and spectrum. The rapid variation of Lorentz factor and the values of photospheric radii that are relatively farther away from the central engine in Phase 2 are more consistent with the mechanism of collisional heating in baryonic jets. Further information can be revealed by combining more wavelengths with the help of the other detectors.

View original: http://arxiv.org/abs/1209.4393