Sudden Spin Slowing in 2005 of Pulsar PSR J0738-4042 Probably due to Asteroid Impacts

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

Authors:

Yu et al

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 −1.14×10−14 s−2. After September 2005, the derivative began to rise up. About 1000 days later, it arrived at another relatively stable value of about −0.98×10−14 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 4.0×109 cm, which is smaller than the tidal disruption radius (4.9×1010 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.