Faraday rotation of the supernova remnant G296.5+10.0: Evidence for a Magnetized Progenitor Wind

TL;DR

This study uses radio spectropolarimetry and RM synthesis to map the magnetic field structure of supernova remnant G296.5+10.0, providing evidence for a magnetized stellar wind from its progenitor star influencing its morphology.

Contribution

It presents the first detailed RM map of G296.5+10.0 and proposes that the remnant's magnetic field pattern results from a magnetized progenitor wind, a novel explanation for its observed RM and morphology.

Findings

RM pattern shows a clear azimuthal magnetic field structure.

The magnetic field likely originates from a magnetized stellar wind of the progenitor.

The observed bilateral symmetry may be due to expansion into a magnetized wind.

Abstract

We present spectropolarimetric radio images of the supernova remnant (SNR) G296.5+10.0 at frequencies near 1.4 GHz, observed with the Australia Telescope Compact Array. By applying rotation measure (RM) synthesis to the data, a pixel-by-pixel map of Faraday rotation has been produced for the entire remnant. We find G296.5+10.0 to have a highly ordered RM structure, with mainly positive RMs (mean RM of +28 rad/m**2) on the eastern side and negative RMs (mean RM of -14 rad/m**2) on the western side, indicating a magnetic field which is directed away from us on one side and toward us on the other. We consider several possible mechanisms for creating the observed RM pattern. Neither Faraday rotation in foreground interstellar gas nor in a homogeneous ambient medium swept up by the SNR shell can easily explain the magnitude and sign of the observed RM pattern. Instead, we propose that the observed RMs are the imprint of an azimuthal magnetic field in the stellar wind of the progenitor star. Specifically, we calculate that a swept-up magnetized wind from a red supergiant can produce RMs of the observed magnitude, while the azimuthal pattern of the magnetic field at large distances from the star naturally produces the anti-symmetric RM pattern observed. Expansion into such a wind can possibly also account for the striking bilateral symmetry of the SNR's radio and X-ray morphologies.