Re-detection and a Possible Time Variation of Soft X-ray Polarisation from the Crab

TL;DR

This study re-detected soft X-ray polarization from the Crab nebula after 40 years using a CubeSat, revealing a potential link between pulsar glitches and polarization changes, which could inform models of high-energy astrophysical phenomena.

Contribution

It presents the first re-detection of soft X-ray polarization from the Crab nebula in decades and suggests a possible connection between pulsar glitches and polarization variation.

Findings

Polarization fraction decreased after the 2019 pulsar glitch.

The nebular polarization remained constant within uncertainties.

The phenomenon lasted about 100 days.

Abstract

The Crab nebula is so far the only celestial object with a statistically significant detection in soft x-ray polarimetry, a window that has not been explored in astronomy since the 1970s. However, soft x-ray polarimetry is expected to be a sensitive probe of magnetic fields in high energy astrophysical objects including rotation-powered pulsars and pulsar wind nebulae. Here we report the re-detection of soft x-ray polarisation after 40 years from the Crab nebula and pulsar with PolarLight, a miniature polarimeter utilising a novel technique onboard a CubeSat. The polarisation fraction of the Crab in the on-pulse phases was observed to decrease after a glitch of the Crab pulsar on July 23, 2019, while that of the pure nebular emission remained constant within uncertainty. The phenomenon may have lasted about 100 days. If the association between the glitch and polarisation change can be confirmed with future observations, it will place strong constraints on the physical mechanism of the high energy emission and glitch of pulsars.