A new wideband radio polarization observation of the Supernova Remnant G315.4$-$2.3

Abstract

The supernova remnant (SNR) G315.4$-$2.3 (MSH 14$-$63 or RCW 86) exhibits strong emission across the electromagnetic spectrum. Radio polarization observations probe magnetic fields and will help to understand the evolution of the SNR. We aim to investigate the radio spectrum and magnetic field properties of the SNR. We observed G315.4$-$2.3 using the Australia Telescope Compact Array (ATCA), covering the frequency range of 1.1-3.1 GHz. We performed rotation measure (RM) synthesis on the $Q$ and $U$ frequency cubes to obtain polarized intensity and RM. The regular component of the line-of-sight magnetic field was estimated from RM. The fractional polarization versus wavelength squared was used to constrain the properties of the turbulent magnetic field. We obtained image cubes of Stokes $I$, $Q$, and $U$, along with images of polarized intensity $P$, RM, and fractional polarization $p$. The radio spectra are very similar for different areas of the SNR. The foreground RM was estimated to be 55 rad m$^{-2}$, and the internal RM of most SNR areas is less than about 50 rad m$^{-2}$. The regular magnetic field along the line of sight was estimated to be about 1.4 $μ$G in the southwest, much smaller than the total magnetic field. For most parts of the southwest and northeast, $p$ is less than 8% and is nearly constant with $λ^2$. We estimated the ratio of turbulent to regular magnetic field to be larger than about 3. The scale of the turbulent magnetic field for some area in the northwest might be smaller than about 0.4 pc. The radio characteristics, including spectrum and turbulent magnetic field, are very similar in the northeast and southwest, even though the evolution is quite different for these two regions based on the current models. These should be taken into account for future modeling of the evolution of the SNR.