Zdenka, Randy Cooper and I just completed a study of He-rich bursts from 4U 1728-34, which can occur as frequently as once every 2 hours. This rate cannot be matched by even the most optimistic ignition models. Although in principle these bursts could be used as indicators of additional heat sources contributed from the core or crust (that was our initial hope), it now seems more likely that some other mechanism is responsible for their frequency, perhaps because accretion does not cover the entire neutron star. Zdenka's paper has now been accepted by ApJ, and is available at arXiv:1005.4729.

Labels: 2010, thermonuclear bursts