Hydrodynamic Thermonuclear Runaways in Superbursts

摘要

We calculate the thermal and dynamical evolution of the surface layers of anaccreting neutron star during the rise of a superburst. For the first few hoursfollowing unstable 12C ignition, the nuclear energy release is transported byconvection. However, as the base temperature rises, the heating time becomesshorter than the eddy turnover time and convection becomes inefficient. Thisresults in a hydrodynamic nuclear runaway, in which the heating time becomesshorter than the local dynamical time. Such hydrodynamic burning can driveshock waves into the surrounding layers and may be the trigger for the normalX-ray burst found to immediately precede the onset of the superburst in bothcases where the Rossi X-Ray Timing Explorer was observing.