X-ray Polarization Detection of the Pulsar Wind Nebula in G21.5-0.9 with IXPE

TL;DR

This study reports the first detection of X-ray polarization in the pulsar wind nebula G21.5-0.9 using IXPE, revealing a highly polarized central structure and providing insights into turbulence and particle acceleration mechanisms.

Contribution

It presents the first X-ray polarization measurement of G21.5-0.9's PWN, demonstrating a stable polarization pattern and highlighting differences with radio polarization maps, advancing understanding of PWN turbulence.

Findings

Detected ~10% polarization degree at ~33° orientation.

Found no significant energy-dependent polarization variation.

Revealed a polarized central torus indicating low turbulence.

Abstract

We present the X-ray polarization observation of G21.5-0.9, a young Galactic supernova remnant (SNR), conducted with the Imaging X-ray Polarimetry Explorer (IXPE) in October 2023, with a total livetime of approximately 837 ks. Using different analysis methods, such as a space-integrated study of the entire region of the PWN and a space-resolved polarization map, we detect significant polarization from the pulsar wind nebula (PWN) at the center of the SNR, with an average polarization degree of ~10% oriented at ~33{\deg} (north through east). No significant energy-dependent variation in polarization is observed across the IXPE band (2-8 keV). The polarization map, corrected for the effect of polarization leakage, reveals a consistent pattern in both degree and angle, with little change across the nebula. Our findings indicate the presence of a highly polarized central torus, suggesting low levels of turbulence at particle acceleration sites. Unlike Vela, but similar to the Crab Nebula, we observe substantial differences between radio and X-ray polarization maps. This suggests a clear separation in energy of the emitting particle populations and hints at an important, yet poorly understood, role of instabilities in the turbulence dynamics of PWNe.