X-ray bursts - Some recent developments

Abstract

In this paper we review recent developments in the areas of burst recurrence, and mass-radius relations of neutron stars. We reach the surprising conclusion that the time-averaged X-ray luminosity emitted in type 1 bursts is approximately independent of the persistent X-ray luminosity over a large range (factor of ~30) of the latter. We conclude that (i) either the persistent X-ray flux is not a good measure of the mass-accretion rate (i.e., the large differences in the persistent flux are due to large differences in anisotropy of the persistent emission without affecting the anisotropy of the burst emission; that seems rather stranger) or (ii) that the rate at which accreted matter is consumed in thermonuclear flashes is approximately independent of the rate at which it is accreted, and that is also rather puzzling. We also discuss how the mass and radius of neutron stars in burst sources can be determined from the bursts, and the associated uncertainties that are presently limiting factors in these determinations.