Andrew Cumming: Long thermonuclear flashes and the heating and composition of neutron star crusts

Andrew Cumming kicked off the workshop with a germane review of type I X-ray bursts, thermonuclear flashes on accreting neutron stars.  X-ray bursts are of great interest because some bursts, specifically those for which hot CNO cycle burning does not set the temperature of the ignition region, can be useful probes of the interior temperature and thereby the crust and core properties.

There are both great successes and failures in comparisons between observations and model results of "normal" H- and He-triggered bursts.  Generally, models of individual bursts agree well with observations (e.g., GS 1826-24), whereas models of global bursting behavior disagree.

Superbursts, extremely energetic flashes thought to be triggered by carbon burning, may be particularly useful probes of crust physics.  Models predict that all crust & core parameters "must be turned to hot," to match observations, but the same predictions are inconsistent with complementary observations of other phenomena.  What's the solution: More exothermic electron captures? a resonance in the carbon fusion reaction rate? strange stars? a new source of shallow heating?

We'll more about these possibilities in the next couple of days.  Stay tuned!