The Possibility of a Detonative Shell Flash on a Neutron Star and a Gamma-Ray Burst

Recent observations of gamma-ray bursts (e.g., X-ray precursor, X-ray tail, and cyclotron lines observed by Ginga) strongly suggest that the gamma-ray burst source is associated with a magnetized neutron star. Here we present results of numerical simulations of shell flashes of a mass-accreting neutron star. Models with a mass accretion rate dM/dt greater than 10 exp -13 solar mass/yr do not trigger a detonative wave. A model with dM/dt greater than 10 exp -15 solar mass/yr is marginal, and its recurrence time is around 10 exp 6 yr, so that the detonative wave model is statistically inconsistent. An alternative mechanism of energy conversion would be an Alfven wave generated in a convective region of a deflagration wave. In this case, the Alfven wave is generated by a vibration of the magnetic field in the convective region where the thermal pressure is larger than the magnetic pressure. The amplitude of the Alfven wave is determined by the convective heat transport efficiency, and its strength is weaker but its duration is longer than the case of a detonation shock wave.