The radio emission from radiative filaments of Cygnus Loop

TL;DR

This study used VLA observations to analyze radio emissions from filaments in the Cygnus Loop supernova remnant, revealing thermal radiation characteristics in radiative filaments contrary to typical non-thermal SNR emissions.

Contribution

It provides the first radio spectral analysis of radiative filaments in Cygnus Loop, showing they emit predominantly thermal bremsstrahlung radiation.

Findings

Radiative filaments detected at 1 and 5 GHz show thermal spectral slopes.

Non-radiative optical filaments were not detected in radio frequencies.

Radiative filaments emit more like HII regions than typical SNRs.

Abstract

The Galactic supernova remnant (SNR) Cygnus Loop emerges as an ideal laboratory for analyzing the different radiation mechanisms, as well as the particle acceleration mechanisms at different types of shocks. In order to determine radio spectral indices of non-radiative and radiative filaments in Cygnus Loop, we observed previously optically analyzed filaments with the Karl G. Jansky Very Large Array (VLA). At 1 and 5 GHz, we detected only radiative filaments in the field of view. Non-radiative optical filaments are also present, but were not detected in radio. Contrary to the expected non-thermal spectral slopes characteristic of SNRs, we instead observed spectral slopes characteristic of the thermal radiation mechanism from the radiative filaments in Cygnus Loop. These evolutionary older parts of Cygnus Loop radiate at radio frequencies predominantly via the thermal bremsstrahlung mechanism, and in that sense their emission more closely resembles the radio emission of HII regions rather than the radio emission of SNRs.