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D. Marsden (NASA/GSFC), R.E. Lingenfelter (CASS/UCSD), R.E. Rothschild (CASS/UCSD)
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 produces 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. We find that a simplified model of the accretion torque involving a constant mass accretion rate can explain the age and period derivative of the pulsar for reasonable values of the pulsar magnetic field and accretion rate.
D.M. acknowledges the support of a National Research Council Research Associateship hosted by the NASA/Goddard Space Flight Center, and R.E.L and R.E.R. acknowledge support from NASA.
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