The Dipole Magnetic Field and Spin-down Evolutions of the High Braking Index Pulsar PSR J1640–4631

Abstract

Abstract In this work, we interpreted the high braking index of PSR J1640−4631 with a combination of the magneto-dipole radiation and dipole magnetic field decay models. By introducing a mean rotation energy conversion coefficient , the ratio of the total high-energy photon energy to the total rotation energy loss in the whole life of the pulsar, and combining the pulsar’s high-energy and timing observations with a reliable nuclear equation of state, we estimate the pulsar’s initial spin period, ms, corresponding to the moment of inertia g cm2. Assuming that PSR J1640−4631 has experienced a long-term exponential decay of the dipole magnetic field, we calculate the true age , the effective magnetic field decay timescale , and the initial surface dipole magnetic field at the pole of the pulsar to be 2900−3100 yr, yr, and G, respectively. The measured braking index of for PSR J1640−4631 is attributed to its long-term dipole magnetic field decay and a low magnetic field decay rate, G yr−1. Our model can be applied to both the high braking index ( ) and low braking index ( ) pulsars, tested by the future polarization, timing, and high-energy observations of PSR J1640−4631.