Binary Sub-Millisecond Pulsar and Rotating Core Collapse Model for SN1987A

Abstract

The recent discovery of a binary sub-millisecond pulsar in SN1987A strongly suggests that the rotation was important in the core collapse of the progenitor of SN1987A. The observed period of the pulsar 0.5079680 ms is close to the maximum rotation of the neutron star. The periodic modulation of the pulse period with 8 hours suggests the existence of the companion with an almost circular orbit. The mass of the companion is either ~ 1.4 Me (face-on) or ~ 10Me (edge-on) with the semi-major axis of ~2 x lOll cm. In either case, if the companion has existed before the supernova explosion, it is hard to understand why the companion has a circular orbit. The formation of the companion after the bounce of the core is proposed. If the angular momentum of the pre-supernova core is greater than ~ 6 x 10 cgs, the core fragments and a binary proto neutron star is formed. As the separation of two neutron stars decreases in several seconds, the larger mass neutron star begins to accrete the matter of the smaller mass neutron star. The sub-millisecond period of the pulsar is· the consequence of the accretion of matter with the angular momentum ~ 10 cgs. Due to the fidal disruption at the end of the accretion, the system consists of a central neutron star and a rotating thin disk. Similar to the formation of planets in the solar nebula, a Jupiter-like secondary of mass ~ 10Me with a circular orbit ·may be formed within a year at separation of ~ lOll cm. A possible detection of the gravitational radiation from the sub-millisecond pulsar and a possible origin of gamma ray bursters are also demonstrated.