On the Physics of Type I X-Ray Bursts on Accreting Neutron Stars at High Accretion Rates

Abstract

We investigate the effect of the hot CNO cycle breakout reaction O-15(alpha, gamma)Ne-19 on the occurrence of type I X-ray bursts on accreting neutron stars. For f(rp) less than or similar to 0.1 where f(rp) is a dimensionless factor by which we multiply the O-15(alpha, gamma)Ne-19 reaction rate of Caughlan & Fowler, our model predicts that bursts should occur only for accretion rates below a critical value approximate to 0.3M(Edd). This agrees with observations. For larger values of f(rp), including the standard choice, the model switches to a new regime in which bursts occur all the way up to M rp. Since the latter regime disagrees with observations, we suggest that the true O-15(alpha, gamma)Ne-19 reaction rate is. M Edd lower than usually assumed.