X-ray observations of SAXJ1808 in quiescence put tight upper limits on the luminosity of thermal emission from the neutron star surface, indicating that the surface is quite cold. It has been suggested that this can be explained by having a high mass neutron star (which can give a higher neutrino emissivity).
Recent optical observations of SAXJ1808 have, however, constrained the mass of the neutron star, and it seems to have a low (rather than high) mass.
To complicate things further, another transient, Aql X-1, which seems to have a surface temperature (from quiescent X-ray observations) consistent with standard cooling, may have a high neutron star mass......so it might have been expected to be colder than actually observed.
Craig asked if anyone had any ideas on how to explain this........particularly, can more massive neutron stars emit less neutrinos than lighter neutron stars?
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