X-ray polarimetry of the Crab nebula with PolarLight: polarization recovery after the glitch and a secular position angle variation

TL;DR

This study uses X-ray polarimetry to observe the Crab nebula, revealing polarization recovery after a pulsar glitch and indicating a long-term evolution of polarization angle over decades.

Contribution

It provides the first follow-up polarization measurements post-glitch and identifies a secular change in polarization angle over 42 years.

Findings

Polarization recovered roughly 100 days after the glitch

Measured polarization angle differs by 18 degrees from 42 years ago

Indicates long-term secular evolution of polarization angle

Abstract

We report follow-up observations of the Crab nebula with the PolarLight X-ray polarimeter, which revealed a possible variation in polarization associated with a pulsar glitch in 2019. The new observations confirm that the polarization has recovered roughly 100 days after the glitch. With the new observations, we find that the polarization angle (PA) measured with PolarLight from the total nebular emission has a difference of 18.0 +- 4.6 (deg) from that measured 42 years ago with OSO-8, indicating a secular evolution of polarization with either the Crab nebula or pulsar. The long-term variation in PA could be a result of multiple glitches in the history, magnetic reconnection or movement of synchrotron emitting structures in the nebula, or secular evolution of the pulsar magnetic geometry.