Relativistic Particle-In-Cell Simulation Studies of Prompt and Early Afterglows from GRBs

TL;DR

This paper uses relativistic Particle-In-Cell simulations to study particle acceleration and magnetic field generation in shocks of gamma-ray bursts, revealing jitter radiation as a key emission mechanism.

Contribution

It demonstrates that the Weibel instability generates small-scale magnetic fields leading to jitter radiation, offering new insights into GRB emission spectra.

Findings

Weibel instability creates non-uniform magnetic fields in relativistic shocks.

Jitter radiation differs from traditional synchrotron emission.

Simulations show particle acceleration occurs within downstream jets.

Abstract

Nonthermal radiation observed from astrophysical systems containing relativistic jets and shocks e.g. gamma-ray bursts (GRBs) active galactic nuclei (AGNs) and microquasars commonly exhibit power-law emission spectra. Recent PIC simulations of relativistic electron-ion (or electron-positron) jets injected into a stationary medium show that particle acceleration occurs within the downstream jet. In collisionless relativistic shocks particle (electron, positron and ion) acceleration is due to plasma waves and their associated instabilities (e.g. the Weibel (filamentation) instability) created in the shock region. The simulations show that the Weibel instability is responsible for generating and amplifying highly non-uniform small-scale magnetic fields. These fields contribute to the electron's transverse deflection behind the jet head. The resulting ``jitter'' radiation from deflected electrons has different properties compared to synchrotron radiation which assumes a uniform magnetic field. Jitter radiation may be important for understanding the complex time evolution and/or spectra in gamma-ray bursts, relativistic jets in general and supernova remnants.