Astronomy

Pulsar Glitches

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Science  07 Jul 2000:
Vol. 289, Issue 5476, pp. 13
DOI: 10.1126/science.289.5476.13c

Only five anomalous x-ray pulsars (AXPs) have been discovered in the universe. These pulsars are thought to be neutron stars spinning with periods of 5 to 12 seconds. The pulsations may be related to an extremely strong magnetic field or to emissions from an accretion disk (either in an intact binary system or from the remnants after a neutron star has swallowed its companion). Although none of the five AXPs appear to be binary systems, evidence for the magnetic field source has been lacking.

Kaspi et al. have observed a glitch (a transient acceleration) in the 11-second spin period of AXP IRXS J170849.0-400910 with the Rossi x-ray timing explorer (RXTE). This glitch is similar to those seen in radio pulsars, which may be rapidly spinning neutron stars with strong magnetic fields. These glitches could be created by breaking of the magnetic dipole; this would apply a torque to the crust, which usually is decoupled from superfluid vortices in the star's interior. During a glitch, however, the vortices would couple briefly with the crust and transfer angular momentum to the surface, thereby increasing its observed spin. Thus, the observation of glitches supports a strong magnetic field interaction in these anomalous neutron stars. — LR

Astrophys. J., in press [astro-ph/0005326].

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