Radio pulsars are thought to spin-down primarily due to torque from magnetic dipole radiation ( MDR ) emitted by the time-varying stellar magnetic field as the star rotates .
This assumption yields a ‘ characteristic age ’ for a pulsar which has generally been assumed to be comparable to the actual age .
Recent observational limits on the proper motion of pulsar B1757–24 , however , revealed that the actual age ( > 39 kyr ) of this pulsar is much greater than its MDR characteristic age ( 16 kyr ) – calling into question the assumption of pure MDR spin-down for this and other pulsars .
To explore the possible cause of this discrepancy , we consider a scenario in which the pulsar acquired an accretion disk from supernova ejecta , and the subsequent spin-down occurred under the combined action of MDR and accretion torques .
A simplified model of the accretion torque involving a constant mass inflow rate at the pulsar magnetosphere can explain the age and period derivative of the pulsar for reasonable values of the pulsar magnetic field and inflow rate .
We discuss testable predictions of this model .