Radiation from an asteroid--neutron star collision

We calculate a zero impact parameter collision of a 5 x 1017 gasteroid with a 1.51 M/sub sun/ neutron star using a two-dimensional Lagrangian-Eulerian hydrodynamics code. The radiation transfer is followed with a Planckian LTE diffusion model, and allowed to couple to the matter through bremsstrahlung and Compton processes. The effects self-gravity on the asteroid, relativity, and magnetic fields are not included. The kinetic energy of impact is converted into radiant energy within 1 ms of impact. However, the neutron star is rapidly (<1 ms) covered by a low-density optically thick cloud that radiates within an order of magnitude of the Eddington limit at an effective temperature of only a few keV. Thus, such models, without the inclusion of confinement effects such as magnetic fields, are insufficient to explain cosmic γ-ray bursts or the 1979 March 5 event