Gamma ray bursts and neutron star accretion of a solid body

The sequence of events that would probably take place if a comet or asteroid were to make a direct impact with a neutron star is described. We have in mind an explanation of the 1979 March 5 gamma burst where a 0.1 s bursts of hard X-rays was followed by a protracted 8 s pulsation. We assume a local 100 pc origin, a cold magnetized neutron star, impacted by a comet or asteroid of 1018 g with finite strength (or binding energy) s10 in units of 1010 dynes cm-2. Then tidal breakup occurs at a radius approx.2 x 109s10/sup -1/3/ cm, and the subsequent flow is compressive and elongates the body. Impact with a neutron star without a magnetic field leads to a small efficiency (< or approx. =10-3) of high temperature radiation because of rapid reconversion of thermal energy to kinetic energy by radiation-stress induced expansion. Only a strong magnetic field can restrain this expansion. Impact of the gravitationally distorted body on a dipole field leads to diamagnetic penetration to approx.50 R/sub ns/, R/sub ns/ the neutron star radius, where a weak shock compresses the body to rhoroughly-equal10rho0 (rho0 the original density) and heat it to a temperature approx.50 eV by the time it reaches Rroughly-equal27 R/sub ns/. The subsequent flow is adiabatic, with compression in magnetic longitude and expansion in magnetic latitude so that the body impacts the surface with a density approx.106 g cm-3, as a thin (several millimeters) diamagnetic slice in longitude, several kilometers wide in latitude, during a time of a millisecond. The neutron star surface interaction causes a local explosion and expansion of matter onto a fan of flux tubes. The restricted area, the fall back at the conjugate field points, and storage of matter at high L or flux surface radii result in a spectrum and flux that offers a reasonable explanation of the March 5 event