Study of eclipses for Redback pulsar J1227$-$4853

TL;DR

This study investigates the eclipse properties of the redback millisecond pulsar J1227-4853 across multiple frequencies, revealing eclipse durations, electron densities, and flux variations, suggesting cyclotron absorption and plasma blobs as causes.

Contribution

It provides detailed measurements of eclipse durations, electron densities, and flux fading, proposing a new explanation involving plasma blobs from mass loss at L2 point.

Findings

Eclipses last about 37% of the orbit at 607 MHz.

Electron column density at eclipse boundaries is approximately 24.4 x 10^{16} cm^{-2}.

Flux fading near inferior conjunction suggests plasma blob absorption.

Abstract

We present a multi-frequency study of eclipse properties of a transitional redback millisecond pulsar J1227$-$4853 discovered in 2014 with the GMRT. Emission from this pulsar is eclipsed at 607 MHz for about 37% of its orbit around the superior conjunction. We observe eclipse ingress and egress transition which last 12% and 15% of its orbit respectively, resulting in only 36% of the orbit being unaffected by eclipsing material. We report an excess dispersion measure (DM) at eclipse boundaries of 0.079(3) pc cm$^{-3}$ and the corresponding electron column density (N$_e$) is 24.4(8) x 10$^{16}$ cm$^{-2}$. Simultaneous timing and imaging studies suggests that the eclipses in J1227$-$4853 are not caused by temporal smearing due to excess dispersion and scattering but could be caused by removal of pulsar flux due to cyclotron absorption of the pulsed signal by intra-binary material constraining the companion's magnetic field. Additionally, near inferior conjunction at orbital phase 0.71 and 0.82 the pulsed emission is significantly delayed which is associated with a fading of the pulsed and continuum flux densities. At orbital phase $\sim$0.82, we measure a change in DM of 0.035(3) pc cm$^{-3}$ and N$_e$ of 10.8(8) x 10$^{16}$ cm$^{-2}$ associated with a dimming of up to $\sim$30% of the peak flux density. Such flux fading around a fixed orbital phase is not reported for other eclipsing binaries. Moreover, this event around inferior conjunction could be caused by absorption of pulsed signal by fragmented blobs of plasma generated from mass loss through the L2 Lagrangian point.