A comparative analysis of disruptive type-I X-ray bursts with non-monotonic decays

Abstract

Previously, only 5 type-I X-ray bursts with variability in the burst decay were known. During a systematic search through the archive of automatically observed triggers of the Swift X-ray observatory, 3 additional bursts were found that show strong variability ($\sim$70\% amplitude), making a total of 8 bursts that show this behaviour. 4 bursts that were observed with Swift (one of which was already known to show variability) are discussed in detail and compared with 4 previously known bursts. We find many similarities. They are likely all ultra compact X-ray binaries, the bursts are all intermediate duration bursts and probably have superexpansion. We speculate that the fluctuations and eclipse-like features are caused by a resettling accretion disk that was disrupted by the effects of super-Eddington fluxes, including an expanding shell and a strong radiation pressure.