  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.
