Rotational and radio emission properties of PSR J0738-4042 over half a century

TL;DR

This study provides a detailed analysis of PSR J0738-4042's rotational and emission behaviors over 50 years, revealing stable profile variations and challenging existing models, suggesting possible asteroid interactions or magnetospheric state changes.

Contribution

It offers the first long-term, comprehensive modeling of the pulsar's spin-down and profile evolution, incorporating Gaussian process regression and analyzing archival data.

Findings

No new correlated spin-down or profile events detected.

Disappearance of a bright emission component was not linked to spin-down changes.

Profile variations are consistent across frequencies and polarizations.

Abstract

We present a comprehensive study of the rotational and emission properties of PSR J0738$-$4042 using a combination of observations taken by the Deep Space Network, Hartebeesthoek, Parkes (Murriyang) and Molonglo observatories between 1972 and 2023. Our timing of the pulsar is motivated by previously reported profile/spin-down events that occurred in September 2005 and December 2015, which result in an anomalously large braking index of $n = 23300 \pm 1800$. Using a Gaussian process regression framework, we develop continuous models for the evolution of the pulsar spin-down rate ($\dot{\nu}$) and profile shape. We find that the pulse profile variations are similar regardless of radio observing frequency and polarisation. Small-scale differences can be ascribed to changes in the interstellar medium along the line of sight and frequency-dependent changes in magnetospheric radio emission height. No new correlated spin-down or profile events were identified in our extended dataset. However, we found that the disappearance of a bright emission component in the leading edge of archival profiles between 1981-1988 was not associated with a substantial change in $\dot{\nu}$. This marks a notable departure from the previous profile/spin-down events in this pulsar. We discuss the challenges these observations pose for physical models and conclude that interactions between the pulsar and in-falling asteroids or a form of magnetospheric state-switching with a long periodicity are plausible explanations.