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R.L. Cooper, R. Narayan (Harvard-Smithsonian, CfA)
Superbursts are energetic (~1042-1043 ergs) thermonuclear flashes on the surface of accreting neutron stars and are thought to be caused by unstable carbon burning. We have conducted a global linear stability analysis of the accreted fuel to determine the conditions under which superbursts occur. We can reproduce the general observational characteristics of superbursts, including burst fluences, recurrence times, and the absence of bursts on stars with accretion rates below roughly 10% of the Eddington limit. By comparing our results with observations, we are able to set constraints on neutron star parameters such as the radius and neutrino cooling mechanism in the core, as well as the composition of the ashes where superbursts are triggered. Specifically, we find that accreting neutron stars with highly efficient neutrino emission (due to direct URCA or pionic reactions, for example) produce extremely energetic (>1044 ergs) superbursts which are inconsistent with observations, while stars with less efficient neutrino emission (due to modified URCA reactions, for example) produce bursts with fluences consistent with those observed.
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Bulletin of the American Astronomical Society, 36 #3
© 2004. The American Astronomical Soceity.