Radiative Mechanisms in GRB prompt emission

Motivated by the Fermi gamma-ray space telescope results, in recent years immense efforts were given to understanding the mechanism that leads to the prompt emission observed. The failure of the optically thin emission models (synchrotron and synchrotron self Compton) increased interest in alternative models. Optically thick models, while having several advantages, also face difficulty in capturing several key observables. Theoretical efforts are focused in two main directions: (1) mechanisms that act to broaden the Planck spectrum; and (2) combining the optically thin and optically thick models to a hybrid model that could explain the key observables.Comment: 9 pages, 2 figures, 1 table; Invited review, to appear in the proceedings of the Gamma-Ray Burst Symposium 2012- IAA-CSIC - Marbella, editors: Castro-Tirado, A. J., Gorosabel, J. and Park, I.

Compactly supported Hamiltonian loops with non zero Calabi invariant

We give examples of compactly supported Hamiltonian loops with non zero Calabi invariant on certain open symplectic manifolds.Comment: 12 page

Constraining Magnetization of Gamma-Ray Bursts Outflows using Prompt Emission Fluence

I consider here acceleration and heating of relativistic outflow by local magnetic energy dissipation process in Poynting flux dominated outflow. Adopting the standard assumption that the reconnection rate scales with the Alfven speed, I show here that the fraction of energy dissipated as thermal photons cannot exceed (13 $\hat \gamma -14)^{-1} = 30$% (for adiabatic index $\hat \gamma = 4/3$) of the kinetic energy at the photosphere. Even in the most radiatively efficient scenario, the energy released as non-thermal photons during the prompt phase is at most equal to the kinetic energy of the outflow. These results imply that calorimetry of the kinetic energy that can be done during the afterglow phase, could be used to constrain the magnetization of gamma-ray bursts (GRB) outflows. I discuss the recent observational status, and its implications on constraining the magnetization in GRB outflows.Comment: (Very) extensive discussions about current observational constraints, implications and limitations. Accepted for publication in the Astrophysical Journa