Computation of synthetic spectra from simulations of relativistic shocks

TL;DR

This paper introduces an efficient method for computing synthetic photon spectra from relativistic shock simulations, leveraging the photon formation length to improve accuracy and computational performance.

Contribution

The paper presents a novel algorithm based on photon formation length that accurately computes spectra from PIC simulation data, filtering out artifacts caused by limited resolution.

Findings

The method effectively identifies intrinsic spectral features.

It reduces computational costs compared to traditional Lienard-Wiechart approaches.

It can analyze spectra from turbulent electromagnetic fields or discrete trajectories.

Abstract

Particle-in-cell (PIC) simulations of relativistic shocks are in principle capable of predicting the spectra of photons that are radiated incoherently by the accelerated particles. The most direct method evaluates the spectrum using the fields given by the Lienard-Wiechart potentials. However, for relativistic particles this procedure is computationally expensive. Here we present an alternative method, that uses the concept of the photon formation length. The algorithm is suitable for evaluating spectra both from particles moving in a specific realization of a turbulent electromagnetic field, or from trajectories given as a finite, discrete time series by a PIC simulation. The main advantage of the method is that it identifies the intrinsic spectral features, and filters out those that are artifacts of the limited time resolution and finite duration of input trajectories.