Jitter radiation as an alternative mechanism for the nonthermal X-ray emission of Cassiopeia A

TL;DR

This paper proposes jitter radiation as an alternative to synchrotron emission for explaining nonthermal X-ray emission in Cassiopeia A, accounting for turbulence effects and fitting observational data better.

Contribution

It introduces a jitter radiation model that includes turbulence effects and demonstrates its superiority over standard models in fitting X-ray spectra of Cassiopeia A.

Findings

Jitter radiation fits X-ray spectra better than standard models.

It measures turbulence spectral index $ u_B$ and minimum scale $ ext{lambda}_{ m{min}}$.

Best-fit turbulence index $ u_B$ is between 2 and 2.4.

Abstract

Synchrotron radiation from relativistic electrons is usually invoked as the responsible for the nonthermal emission observed in Supernova Remnants (SNRs). Diffusive shock acceleration (DSA) is the most popular mechanism to explain the process of particles acceleration and within its framework a crucial role is played by the turbulent magnetic-field. However, the standard models commonly used to fit X-ray synchrotron emission do not take into account the effects of turbulence in the shape of the resulting photon spectra. An alternative mechanism that properly includes such effects is the jitter radiation, that provides for an additional power-law beyond the classical synchrotron cutoff. We fitted a jitter spectral model to Chandra, NuSTAR, SWIFT/BAT and INTEGRAL/ISGRI spectra of Cassiopeia A and found that it describes the X-ray soft-to-hard range better than any of the standard cutoff models. The jitter radiation allows us to measure the index of the magnetic turbulence spectrum $\nu_B$ and the minimum scale of the turbulence $\lambda_{\rm{min}}$ across several regions of Cas A, with best-fit values $\nu_B \sim 2-2.4$ and $\lambda_{\rm{min}} \lesssim 100$ km.