2001ApJ...553..796R -
Astrophys. J., 553, 796-800 (2001/June-1)
Magnetically accreting isolated old neutron stars.
RUTLEDGE R.E.
Abstract (from CDS):
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∝v1/3). 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 kTeff=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.
Abstract Copyright:
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Journal keyword(s):
Stars: Pulsars: General - Stars: Magnetic Fields - Stars: Neutron - X-Rays: Stars
Simbad objects:
1
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