INTEGRAL/IBIS and optical observations of the Crab nebula/pulsar polarisation

TL;DR

This study extends previous gamma-ray polarisation observations of the Crab Nebula using nearly ten years of INTEGRAL/IBIS data, providing improved measurements of polarisation characteristics and comparing them with optical polarisation data.

Contribution

It offers a more detailed analysis of gamma-ray polarisation over a longer period and compares gamma-ray and optical polarisation, enhancing understanding of the nebula's emission mechanisms.

Findings

Refined polarisation fraction and angle measurements.

Spectral energy distribution of polarised gamma-ray component.

Comparison with optical polarisation data.

Abstract

Previous INTEGRAL/IBIS observations have shown that the gamma-ray radiation of the Crab Nebula is highly polarised and remarkably aligned along the axis of rotation of the pulsar (Forot et al. 2008). Their study was based on the first four years of operation of the satellite. Here we present an analysis based upon nearly ten years of operation. This new analysis allows a better characterisation of the polarisation fraction and position angle, as well as a measure of spectral energy distribution of the polarised component. These results are then compared to the known optical polarisation of the pulsar and nearby synchrotron knot. In the future we shall compare the gamma-ray polarisation with the phase-resolved optical polarisation using instruments such as GASP (Kyne et al. 2010).