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

TL;DR

This paper presents advanced relativistic Particle-In-Cell simulations to study particle acceleration and magnetic field generation in shocks related to gamma-ray bursts, revealing insights into jitter radiation mechanisms affecting observed spectra.

Contribution

It introduces new PIC simulation results demonstrating the role of plasma instabilities and small-scale magnetic fields in particle acceleration and radiation in relativistic shocks.

Findings

Weibel instability generates small-scale magnetic fields in shocks.

Jitter radiation differs from synchrotron radiation in spectral properties.

Simulations show electron 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.