About explanations for X-ray bursts with double peaks and precursors

Abstract

Current explanations for X-ray bursts with double peaks and precursors are discussed. Order of magnitude considerations reveal problems with the basic assumptions of proposed models with expanding photospheres. It is found that the low temperature in the outer layers has only a limited influence on the spectrum of the emergent X radiation. The formation of double peaks and precursors from originally single-peaked profiles caused by hyperbolic photon diffusion through marginally optically thick layers is reviewed. It is pointed out that the physics connected with expanding photospheres requires the application of fully relativistic and causal diffusion equations introduced earlier.