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

Understand

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.