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

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 2005 September and 2015 December, which result in an anomalously large braking index of n = 23 300 +/- 1800. Using a Gaussian process regression framework, we develop continuous models for the evolution of the pulsar spin-down rate (nu) over dot and profile shape. We find that the pulse profile variations are similar regardless of radio observing frequency and polarization. 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 data set. However, we found that the disappearance of a bright emission component in the leading edge of archival profiles between 1981 and 1988 was not associated with a substantial change in (nu) over dot. 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.

Automated summary

We conducted a comprehensive study on PSR J0738-4042, analyzing rotational and emission properties using observations from various observatories over a span of 50 years. We developed continuous models using Gaussian process regression to track spin-down rate and pulse profile evolution, finding similarities in profile variations across different observing frequencies and polarizations. No new spin-down or profile events were observed, but the disappearance of a bright emission component was noted without a substantial change in spin-down rate. Possible explanations include interactions with asteroids or magnetospheric state-switching.