Unusual Emission Variations Near the Eclipse of A Black Widow PSR J1720$-$0533

TL;DR

This study presents detailed radio observations of PSR J1720$-$0533 during its eclipse, revealing quasi-periodic emission variations, polarization changes, and potential plasma lensing effects, advancing understanding of pulsar eclipse phenomena.

Contribution

It provides the first detailed measurements of flux, DM, and polarization variations during the eclipse of PSR J1720$-$0533, highlighting plasma lensing and scattering effects.

Findings

Quasi-periodic pulse emission variations with a 22 s period during ingress.

Linear polarization disappears before the eclipse, prior to DM changes.

Pulse scattering may significantly influence the eclipse process.

Abstract

We report on an {unusually} bright observation of PSR J1720$-$0533 using the Five-hundred-meter Aperture Spherical radio Telescope (FAST). The pulsar is in a black widow system that {was discovered by the Commensal Radio Astronomy FAST Survey (CRAFTS). By coincidence, a bright scintillation maximum was simultaneous with the eclipse in our observation which allowed for precise measurements of flux density variations, as well as dispersion measure (DM) and polarization.} We found that there are quasi-periodic pulse emission variations with a modulation period of $\sim$ {22\,s} during the ingress of the eclipse, which could be caused by plasma lensing. {No such periodic modulation was found during the egress of the eclipse. } {The linear polarization of the pulsar disappears before the eclipse, even before there is a visually obvious change in DM. We also found that the pulse scattering maybe play an important role in the eclipse of PSR J1720$-$0533.}