2001ApJ...553..796R

Previous work on the emission from isolated old neutron stars (IONSs) accreting from the interstellar medium (ISM) has focused on gravitational capture–i.e., Bondi accretion. We propose a new class of sources that accrete via magnetic interaction with the ISM. While for the Bondi mechanism the accretion rate M{dot}_Bondi decreases with increasing neutron star velocity, in magnetic accretors (MAGACs) M{dot}_MAGAC increases with increasing neutron star velocity (M{dot}_Bondi∝v^–3 vs. M{dot}_MAGAC∝v^1/3). MAGACs will be produced among high-velocity (≳100 km.s^–1), high magnetic field (B>10¹⁴ G) radio pulsars–the ``magnetars''–after they have evolved first through magnetic dipole spin-down, followed by a ``propeller'' phase (during which the object sheds angular momentum on a timescale ≲10¹⁰ yr). The properties of MAGACs may be summarized thus: dipole magnetic fields of B≳10¹⁴ G; minimum velocities relative to the ISM of 25-100 km.s^–1 or higher, depending on B, well below the median in the observed radio pulsar population; spin periods of greater than days to years; accretion luminosities of 10²⁸-10³¹ ergs.s^–1; and effective temperatures kT_eff=0.3-2.5 keV if they accrete onto the magnetic polar cap. We find no examples of MAGACs among previously observed source classes (anomalous X-ray pulsars, soft gamma-ray repeaters, or known IONs). However, MAGACs may be more prevalent in flux-limited X-ray catalogs than their gravitationally accreting counterparts.