Discovery of a shock-compressed magnetic field in the north-western rim of the young supernova remnant RX J1713.7-3946 with X-ray polarimetry

TL;DR

This study uses X-ray polarimetry to reveal that the magnetic field in the shock regions of the supernova remnant RX J1713.7-3946 is oriented tangentially, providing new insights into magnetic field structure and particle acceleration.

Contribution

First spatially-resolved X-ray polarimetric measurement showing tangential magnetic fields in the SNR RX J1713.7-3946's shock regions, advancing understanding of magnetic field orientation in young supernova remnants.

Findings

Magnetic field in the SNR is oriented tangentially at particle acceleration sites.

Average polarization degree is 12.5%, with localized patches up to 41.5%.

Results support a shock-compressed magnetic field and favor a leptonic origin of gamma-ray emission.

Abstract

Supernova remnants (SNRs) provide insights into cosmic-ray acceleration and magnetic field dynamics at shock fronts. Recent X-ray polarimetric measurements by the Imaging X-ray Polarimetry Explorer (IXPE) have revealed radial magnetic fields near particle acceleration sites in young SNRs, including Cassiopeia A, Tycho, and SN 1006. We present here the spatially-resolved IXPE X-ray polarimetric observation of the northwestern rim of SNR RX J1713.7-3946. For the first time, our analysis shows that the magnetic field in particle acceleration sites of this SNR is oriented tangentially with respect to the shock front. Because of the lack of precise Faraday-rotation measurements in the radio band, this was not possible before. The average measured polarization degree (PD) of the synchtrotron emission is 12.5 {\pm} 3.3%, lower than the one measured by IXPE in SN 1006, comparable to the Tycho one, but notably higher than the one in Cassiopeia A. On sub-parsec scales, localized patches within RX J1713.7-3946 display PD up to 41.5 {\pm} 9.5%. These results are compatible with a shock-compressed magnetic field. However, in order to explain the observed PD, either the presence of a radial net magnetic field upstream of the shock, or partial reisotropization of the turbulence downstream by radial magneto-hydrodynamical instabilities, can be invoked. From comparison of PD and magnetic field distribution with {\gamma}-rays and 12 CO data, our results provide new inputs in favor of a leptonic origin of the {\gamma}-ray emission.