Neutron star disk formation from supernova fall-back and possible observational consequences

Abstract

We have examined a simple model for gravitational fall-back of supernova ejecta to estimate the effect of delayed fall-back on pulsar activity from the central neutron star. Direct dimensional arguments suggest that a Kepler disk will be created with a mass of the order of 10⁻⁵ M⊙ for the probable initial magnetic fields and rotation rates. It has already been argued that such a disk would be required for pulsar action. The disk expected to be formed by fall-back is, at first, too distant to favour pulsar action. We therefore predict a neutron star disk that may be detectable when the nebula around SN1987A clears, although the same model also suggests that the pulsar action might not at first be taking place. Because this disk should be composed of the same sort of shocked and highly processed matter that presently maintains the supernova light curve through radioactive heating, the disk should be hot and luminous, thereby providing a point power-law optical source in the nebula. Thus, observational possibilities include: (1) observation of thermal radiation from the disk, (2) observation of X-rays from a transient episode of accretion on to the neutron star, and (3) a delayed turn-on of the pulsar.