Detection of Linear Polarization in the Radio Remnant of Supernova 1987A

TL;DR

This study reports the first detection of linear polarization in the radio emission of Supernova 1987A, revealing magnetic field structures and cosmic ray acceleration sites through multi-frequency imaging observations.

Contribution

It provides the first polarization measurements of Supernova 1987A's remnant, offering insights into magnetic field orientation and cosmic ray acceleration regions.

Findings

Radial magnetic field across the inner ring.

Peak magnetic field strength at eastern high-emissivity sites.

Polarization fraction of ~3% at 22 and 44 GHz.

Abstract

Supernova 1987A in the Large Magellanic Cloud has proven a unique laboratory to investigate particle acceleration in young supernova remnants. Here we report the first detection of linear polarization of the supernova's synchrotron emission from imaging observations at frequencies spanning from 20 to 50 GHz, carried out with the Australia Telescope Compact Array between October 2015 and May 2016. The direction of the radio polarization, corrected for Faraday rotation, points to a primarily radial magnetic field across the inner ring, encompassing both the reverse and forward shocks. The magnetic field strength peaks over the high-emissivity eastern sites, where efficient cosmic ray acceleration likely takes place under quasi-parallel shocks at high Mach numbers. The mean fraction of polarized emission in the brightest sites is $2.7\pm0.2\%$ at 22 GHz and $3.5\pm0.7\%$ at 44 GHz. In the inner remnant, non-radial components of the polarized emission appear to be more prevalent. However, the low significance detection in the central regions limits interpretation.