X-Ray Polarization in SN 1006 Southwest Shows Spatial Variations and Differences in the Radio Band

Abstract

We report the detection of a spatial variation of X-ray polarization in the southwestern (SW) shell of supernova remnant SN 1006 (SN 1006 SW) using the Imaging X-ray Polarimetry Explorer (IXPE). The shell has an average X-ray polarization degree (PD) of 21.6% ± 4.5% and polarization angle of −48 ^∘ ± 5 ^∘ 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% ± 8% in the south and a significantly lower PD ≲ 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 to ≲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 preexisting ambient magnetic fields.

Keywords

• Supernova remnants
• Polarimetry
• Cosmic rays
• Shocks
• Magnetic fields