X-ray polarization in SN 1006 southwest shows spatial variations and differences with the radio band

TL;DR

This study uses IXPE to reveal spatial variations in X-ray polarization in SN 1006's southwest shell, showing environment-dependent magnetic turbulence and differences between X-ray and radio polarization, advancing understanding of magnetic field structures in supernova remnants.

Contribution

First detection of spatially varying X-ray polarization in SN 1006 SW, linking magnetic turbulence to environment and contrasting X-ray and radio magnetic field structures.

Findings

X-ray polarization degree varies along the shell, peaking at 40%.

Magnetic turbulence scale constrained to less than 0.1 pc.

X-ray and radio polarization trace different magnetic field regions.

Abstract

We report the detection of a spatial variation of X-ray polarization in the southwestern shell of SN 1006 (SN 1006 SW) using IXPE. The shell has an average X-ray polarization degree (PD) of $21.6\%\pm 4.5\%$ and polarization angle (PA) of $-48^\circ \pm 5^\circ$ in the 2--4 keV energy band, similar to those in the northeastern shell. The PD varies along SN 1006 SW, with a peak PD$= 40\%\pm 8\%$ in the south and a significantly lower PD $\lesssim 27\%$ (99\% upper limit) in the west where the shell has been proposed to be interacting with an interstellar cloud. The correlation between the PD, which reflects the magnetic orderliness, and the preshock density provides observational evidence that magnetic turbulence and amplification are environment-dependent. The high PD detected in the southern region of the shell constrains the magnetic turbulence scale of $\lesssim 0.1$~pc. Moreover, by comparing the IXPE X-ray and MeerKAT radio polarization measurements for SN 1006 SW, we found that magnetic fields traced by X-ray polarization are nearly radially distributed, whereas those traced by radio polarization tend to follow a direction parallel to the Galactic plane. This suggests that the X-ray polarization probes freshly amplified magnetic fields from small-scale structures in the immediate postshock region, while the radio traces more extended regions influenced by the pre-existing ambient magnetic fields.