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.

Figures (10)

• Figure 1: $uv$ coverage of the 16 frequency channels centered at 3.023 GHz from all the pointings of G315.4$-$2.3.
• Figure 2: Total intensity ($I$) image and contours of G315.4$-$2.3 at 2.2 GHz from averaging all the frequency channels. The contour levels are at $2^{0.5n}\times5\sigma_I$, $n=0,1,2,\ldots$, and $\sigma_I=0.6$ mJy beam$^{-1}$ is the rms noise. The resolution is $62^{^{\prime\prime}}\times33^{^{\prime\prime}}$. The red dashed lines mark the four regions, for which the spectral indices were derived and shown in Fig. \ref{['fig:g315_4regions_SpecIndex']}.
• Figure 3: Integrated flux density versus frequency for SNR G315.4$-$2.3. Blue points were measured from the 80 $I$ images and red points were from Table \ref{['tab:G315_flux']}.
• Figure 4: The same as Fig. \ref{['fig:g315_SpecIndex']}, but for the four regions marked in Fig. \ref{['fig:total intensity']} and showing only the new measurements from ATCA.
• Figure 5: Image of $|F(\phi_{\rm peak})|$, corresponding to polarized intensity $P$, superimposed with $I$ contours of G315.4$-$2.3. The contour levels are the same as Fig. \ref{['fig:total intensity']}. The bars indicate the orientation of magnetic fields with lengths proportional to $P$.