A new wideband radio polarization observation of the supernova remnant G315.4–2.3

¹ School of Physics and Astronomy, Yunnan University, Kunming 650500, PR China
² SKA Observatory, SKA-Low Science Operations Centre, 26 Dick Perry Avenue, Kensington, WA 6151, Australia
³ Department of Astronomy and Astrophysics, University of California, Santa Cruz, 1156 High Street, Santa Cruz, CA 95064, USA
⁴ Dunlap Institute for Astronomy and Astrophysics, University of Toronto, 50 St. George Street, Toronto, ON M5S 3H4, Canada
⁵ David A. Dunlap Department of Astronomy and Astrophysics, University of Toronto, 50 St. George Street, Toronto, ON M5S 3H4, Canada
⁶ Center for Astrophysics | Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138, USA
⁷ Dominion Radio Astrophysical Observatory, Herzberg Astronomy & Astrophysics, National Research Council Canada, PO Box 248, Penticton, BC V2A 6J9, Canada

^★ Corresponding authors: This email address is being protected from spambots. You need JavaScript enabled to view it. ; This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 5 December 2025
Accepted: 1 March 2026

Abstract

Context. 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 help us understand the evolution of the SNR.

Aims. We investigated the radio spectrum and magnetic field properties of the SNR.

Methods. We observed G315.4-2.3 using the Australia Telescope Compact Array (ATCA), covering the frequency range 1.1-3.1 GHz. We then performed rotation measure (RM) synthesis on the frequency cubes of Q and U to obtain the 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.

Results. We obtained image cubes of Stokes 1, Q, and U over the frequency range 1.319-3.023 GHz after excluding channels affected by radio frequency interference, images of polarized intensity P and RM, and images of fractional polarization p. The rms noise is 0.6 mJy beam⁻¹ for the band-averaged I and is 90 μJy beam⁻¹ for P. All images have been smoothed to a common resolution of 62″ × 33″. The comparison with single-dish observations indicates that our images have retained the larger-scale emission. We obtained a spectral index of α = −0.60 ± 0.03 for the SNR. The radio spectra are very similar for different areas of the SNR. The foreground RM was estimated to be approximately 55 rad m⁻², and the internal RM of most SNR areas is small, less than about 50 rad m⁻². The regular magnetic field along the line of sight was estimated to be about 1.4 μG 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 λ². We estimated the ratio of turbulent to regular magnetic field to be higher than about 3. The scale of the turbulent magnetic field for some areas in the northeast might be smaller than about 0.4 pc.

Conclusions. The radio characteristics, including the 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.