LOFAR detection of faint radio emission from the supernova remnant SRGeJ0023+3625=G116.6-26.1: probing the Milky Way synchrotron halo

TL;DR

This paper reports the detection of faint radio emission from a supernova remnant in the Milky Way halo using LOFAR, providing insights into the halo's thermal and non-thermal components.

Contribution

First detection of radio emission from the SNR G116.6-26.1 with LOFAR, suggesting it as an evolved halo SNR and a probe of the Milky Way's halo components.

Findings

Radio shell coincides with X-ray boundary of the SNR.

Surface brightness is very low, below typical SNRs in the $\

Emission consistent with adiabatic compression model.

Abstract

A supernova remnant (SNR) candidate SRGe~J0023+3625 = G116.6-26.1 was recently discovered in the \textit{SRG}/eROSITA all-sky X-ray survey. This large ($\sim 4$ deg in diameter) SNR candidate lacks prominent counterparts in other bands. Here we report detection of radio emission from G116.6-26.1 in the LOFAR Two-metre Sky Survey (LoTTS-DR2). Radio images show a shell-like structure coincident with the X-ray boundary of the SNR. The measured surface brightness of radio emission from this SNR is very low. Extrapolation of the observed surface brightness to 1~GHz places G116.6-26.1 well below other objects in the $\Sigma-D$ diagram. We argue that the detected radio flux might be consistent with the minimal level expected in the van der Laan adiabatic compression model, provided that the volume emissivity of the halo gas in the LOFAR band is $\sim 10^{-42}\,{\rm Wm^{-3}Hz^{-1} sr^{-1}}$. If true, this SNR can be considered as a prototypical example of an evolved SNR in the Milky Way halo. In the X-ray and radio bands, such SNRs can be used as probes of thermal and non-thermal components constituting the Milky Way halo.