Infrared imaging and polarimetric observations of the pulsar wind nebula in SNR G21.5-0.9

TL;DR

This paper presents infrared and polarimetric observations of the pulsar wind nebula in SNR G21.5-0.9, revealing a limb-brightened iron emission ring and highly polarized emission from the compact nebula, with spectral analysis indicating spectrum flattening between IR and X-ray bands.

Contribution

First infrared imaging and polarimetric study of the pulsar wind nebula in SNR G21.5-0.9, revealing new structural and spectral features.

Findings

Detection of limb-brightened iron emission ring around the nebula

High polarization degree (~47%) of the compact nebula emission

Infrared spectrum suggests flattening between IR and X-ray bands

Abstract

We present infrared observations of the supernova remnant G21.5-0.9 with the Very Large Telescope, the Canada-France-Hawaii Telescope and the Spitzer Space Telescope. Using the VLT/ISAAC camera equipped with a narrow-band [FeII] 1.64um filter the entire pulsar wind nebula in SNR G21.5-0.9 was imaged. This led to detection of iron line-emitting material in the shape of a broken ring-like structure following the nebula's edge. The detected emission is limb-brightened. We also detect the compact nebula surrounding PSR J1833-1034, both through imaging with the CFHT/AOB-KIR instrument (K' band) and the IRAC camera (all bands) and also through polarimetric observations performed with VLT/ISAAC (Ks band). The emission from the compact nebula is highly polarised with an average value of the linear polarisation fraction $P_{L}^{avg} \simeq 0.47$, and the swing of the electric vector across the nebula can be observed. The infrared spectrum of the compact nebula can be described as a power law of index $\alpha_{IR} = 0.7 \pm 0.3$, and suggests that the spectrum flattens between the infrared and X-ray bands.