Nonthermal Signatures of Radiative Supernova Remnants

TL;DR

This paper predicts observable nonthermal emission signatures from supernova remnants during their radiative stage, providing a new method to identify this phase through radio to gamma-ray brightening, which can be detected with current and future telescopes.

Contribution

It introduces a novel observational signal of SNR radiative stage via nonthermal emission from cosmic ray interactions, supported by semi-analytic and hydrodynamic models.

Findings

Nonthermal signatures increase by nearly two orders of magnitude at radiative onset.

Radio and gamma-ray brightening are predicted as detectable signals.

Next-generation telescopes can resolve these nonthermal signatures.

Abstract

The end of supernova remnant (SNR) evolution is characterized by a so-called "radiative" stage, in which efficient cooling of the hot bubble inside the forward shock slows expansion, leading to eventual shock breakup. Understanding SNR evolution at this stage is vital for predicting feedback in galaxies, since SNRs are expected to deposit their energy and momentum into the interstellar medium at the ends of their lives. A key prediction of SNR evolutionary models is the formation at the onset of the radiative stage of a cold, dense shell behind the forward shock. However, searches for these shells via their neutral hydrogen emission have had limited success. We instead introduce an independent observational signal of shell formation arising from the interaction between nonthermal particles accelerated by the SNR forward shock (cosmic rays) and the dense shell. Using a semi-analytic model of particle acceleration based on state-of-the-art simulations coupled with a high-resolution hydrodynamic model of SNR evolution, we predict the nonthermal emission that arises from this interaction. We demonstrate that the onset of the radiative stage leads to nonthermal signatures from radio to $\gamma$-rays, including radio and $\gamma$-ray brightening by nearly two orders of magnitude. Such a signature may be detectable with current instruments, and will be resolvable with the next generation of gamma-ray telescopes (namely, the Cherenkov Telescope Array).