Gamma-ray Burst 080319B: Evidence for Relativistic Turbulence, Not Internal Shocks

TL;DR

This paper presents evidence that the prompt emission of GRB 080319B is better explained by a relativistic turbulence model rather than internal shocks, based on detailed optical and gamma-ray data analysis.

Contribution

It introduces a turbulent source model with random Lorentz factors to explain the prompt emission, challenging the internal shock paradigm for gamma-ray bursts.

Findings

Optical radiation from synchrotron emission by relativistic electrons.

Gamma-ray emission from inverse Compton scattering of synchrotron photons.

Gamma-ray emission was highly variable; optical emission was less variable.

Abstract

We show that the excellent optical and gamma-ray data available for GRB 080319B rule out the internal shock model for the prompt emission. The data instead point to a model in which the observed radiation was produced close to the deceleration radius ($\sim10^{17}$ cm) by a turbulent source with random Lorentz factors $\sim10$ in the comoving frame. The optical radiation was produced by synchrotron emission from relativistic electrons, and the gamma-rays by inverse Compton scattering of the synchrotron photons. The gamma-ray emission originated both in eddies and in an inter-eddy medium, whereas the optical radiation was mostly from the latter. Therefore, the gamma-ray emission was highly variable whereas the optical was much less variable. The model explains all the observed features in the prompt optical and gamma-ray data of GRB 080319B. We are unable to determine with confidence whether the energy of the explosion was carried outward primarily by particles (kinetic energy) or magnetic fields. Consequently, we cannot tell whether the turbulent medium was located in the reverse shock (we can rule out the forward shock) or in a Poynting-dominated jet.