Reduced spin-down rate of PSR J0738-4042 explained as due to an asteroid disruption event

TL;DR

This paper proposes that the observed change in the spin-down rate of pulsar PSR J0738-4042 is caused by the disruption and accretion of an asteroid, providing a self-consistent model that explains the variability.

Contribution

The study introduces a novel explanation for pulsar spin-down rate changes based on asteroid disruption and accretion, linking observational data with a physical model.

Findings

The asteroid disruption can account for the observed spin-down rate change.

The magnetospheric radius is consistent with the disruption scenario.

The model quantitatively matches the observed variability.

Abstract

Long term observations by Brook et al. reveal that the derivative of rotational frequency of PSR J0738-4042 changed abruptly in 2005. Originally, the spin-down rate was relatively stable, with the rotational frequency derivative of $-1.14 \times 10^{-14}~\rm s^{-2}$. After September 2005, the derivative began to rise up. About 1000 days later, it arrived at another relatively stable value of about $-0.98 \times 10^{-14}~\rm s^{-2}$, indicating that the pulsar is spinning-down relatively slowly. To explain the observed spin-down rate change, we resort to an asteroid disrupted by PSR J0738-4042. In our model, the orbital angular momentum of the asteroid is assumed to be parallel to that of the rotating pulsar, so that the pronounced reduction in the spin-down rate can be naturally explained as due to the transfer of the angular momentum from the disrupted material to the central pulsar. The derived magnetospheric radius is about $4.0 \times 10^{9}$ cm, which is smaller than the tidal disruption radius ($4.9 \times 10^{10}$ cm). Our model is self-consistent. It is shown that the variability of the spin-down rate of PSR J0738-4042 can be quantitatively accounted for by the accretion from the asteroid disrupted by the central pulsar.