The Rotational Evolution of the Fastest Spinning Normal Pulsar PSR J0537-6910: Braking by Magnetic Dipole Radiation and Pulsar Wind

Abstract

We study the spin evolution of the young X-ray pulsar PSR J0537-6910 in the Large Magellanic Cloud, the fastest-spinning isolated pulsar known to date with a rotation period of 16 ms, which provides a unique laboratory for probing the early angular momentum evolution of a neutron star. Motivated by the observed discrepancy that most pulsars exhibit less than three braking indices in contrast to what is predicted by a magnetospheric dipolar slow-down law, we propose a hybrid Magnetic Dipole Radiation and Wind (MDRW) model that incorporates both magnetic dipole radiation (MDR) and particle wind contributions. By assuming $n=2$, we derive analytical solutions for the spin evolution equations under different ages (1–4 kyr). We show that the initial spin period range (10.5–14.3 ms) predicted by the MDRW model significantly exceeds the values derived from the classical MDR framework (7.0–14.4 ms), which is in agreement with physical expectations for neutron star birth scenarios. Furthermore, the MDRW model reveals an equal partitioning of rotational energy loss between magnetic dipole radiation and particle wind components ($d=f=0.5$) when $n=2$, highlighting the interplay of the various mechanisms in the spin-down of young pulsars. This also provides a new approach to estimating the period evolution of pulsars.