Gamma Ray Burst Prompt Emission Variability in Synchrotron and Synchrotron Self-Compton Lightcurves

TL;DR

This study compares synchrotron and synchrotron self-Compton (SSC) emission models for gamma-ray bursts, concluding that SSC cannot fully explain the observed gamma-ray variability in GRB 080319B.

Contribution

The paper introduces a combined formalism and simulation approach to analyze the variability of synchrotron and SSC components in GRB emissions, challenging the SSC model's adequacy.

Findings

SSC variability is only moderately amplified compared to synchrotron.

The SSC model cannot fully account for the gamma-ray emission properties of GRB 080319B.

Both formalism and simulation approaches yield consistent results.

Abstract

Gamma Ray Burst prompt emission is believed to originate from electrons accelerated in a highly relativistic outflow. "Internal shocks" due to collisions between shells ejected by the central engine is a leading candidate for electron acceleration. While synchrotron radiation is generally invoked to interpret prompt gamma-ray emission within the internal shock model, synchrotron self-Compton (SSC) is also considered as a possible candidate of radiation mechanism. In this case, one would expect a synchrotron emission component at low energies, and the naked-eye GRB 080319B has been considered as such an example. In the view that the gamma-ray lightcurve of GRB 080319B is much more variable than its optical counterpart, in this paper we study the relative variability between the synchrotron and SSC components. We develop a "top-down" formalism by using observed quantities to infer physical parameters, and subsequently to study the temporal structure of synchrotron and SSC components of a GRB. We complement the formalism with a "bottom-up" approach where the synchrotron and SSC lightcurves are calculated through a Monte-Carlo simulations of the internal shock model. Both approaches lead to the same conclusion. Small variations in the synchrotron lightcurve can be only moderately amplified in the SSC lightcurve. The SSC model therefore cannot adequately interpret the gamma-ray emission properties of GRB 080319B.