On GRB Physics Revealed by FERMI/LAT

TL;DR

This paper analyzes Fermi/LAT observations of gamma-ray bursts to understand their emission mechanisms, emission sites, Lorentz factors, and magnetic fields, suggesting multi-zone emission and inverse Compton processes for high-energy photons.

Contribution

It provides new insights into GRB emission regions, Lorentz factors, and magnetic field amplification based on Fermi/LAT data, challenging previous assumptions.

Findings

High-energy emission likely from inverse Compton process

GRB emission occurs in multiple zones at different radii

Magnetic fields in afterglow shocks are strongly amplified to mG levels

Abstract

We discuss the implications of Fermi/LAT observations on several aspects of gamma-ray burst (GRB) physics, including the radiation process, the emission sites, the bulk Lorentz factor, and the pre-shock magnetic field: (1) MeV-range emission favors synchrotron process but the highest energy (>10GeV) emission may not be synchrotron origin, more likely inverse Compton origin; (2) GRB should have multi-zone emission region, with MeV emission produced at smaller radii while optical and >100MeV emission at larger radii; (3) the bulk Lorentz factor can be a few 100's, much lower than 10^3, in multi-zone model; (4) the upstream magnetic field of afterglow shock is strongly amplified to be at least in mG scale.