Anti-Magnetars: An Exotic New Class of High Energy Pulsars

Eric Gotthelf

(Columbia University)

Central compact objects (CCOs) in supernova remnants (SNRs) are apparently isolated neutron stars, with steady flux, predominantly thermal X-ray emission, lacking an optical or radio counterpart, and without evidence of a pulsar wind nebula. Three are found to be pulsars, with periods of 0.105, 0.112, and 0.424 s. Until now, no spin-down was detected from a CCO, which we interpret as indicating a weak dipole magnetic field. In two cases, the upper limits on the magnetic field inferred from spin period measurements are 3.3e11 G and 9.8e11 G. Recently, we obtained the first definite detection of the spin-down of a CCO, from the 0.105 s pulsar in Kes 79, measuring B = 3.1e10 G, smaller than that of any other young neutron star. Important implications are that the birth periods of the CCO pulsars are not significantly different from their present values, and that their spin-down luminosities are, and have always been, insufficient to generate significant non-thermal magnetospheric emission or synchrotron nebulae. The "characteristic age" has no meaning for CCOs, being millions of years for pulsars that are in SNRs that are only thousands of years old. This suggests that some isolated radio pulsars with weak magnetic fields that have characteristic ages of millions of years may actually be former CCOs that are only moderately aged. Most of the properties of the CCOs can thus be explained by an "anti-magnetar" model, including the possibility that their weak magnetic fields are causally related to their slow rotation periods at birth through the turbulent dynamo that generates the magnetic field. While CCOs are inconspicuous relative to ordinary young pulsars and magnetars, the fact that they are found in SNRs in comparable numbers to other classes of neutron stars implies that they must represent a significant fraction of neutron star births.