Continued Neutron Star Crust Cooling of the 11 Hz X-Ray Pulsar in Terzan 5: A Challenge to Heating and Cooling Models?. (arXiv:1306.2345v1 [astro-ph.HE])

Continued Neutron Star Crust Cooling of the 11 Hz X-Ray Pulsar in Terzan 5: A Challenge to Heating and Cooling Models?. (arXiv:1306.2345v1 [astro-ph.HE]):
The transient neutron star low-mass X-ray binary and 11 Hz X-ray pulsar IGR
J17480-2446 in the globular cluster Terzan 5 exhibited an 11-week accretion
outburst in 2010. Chandra observations performed within five months after the
end of the outburst revealed evidence that the crust of the neutron star became
substantially heated during the accretion episode and was subsequently cooling
in quiescence. This provides the rare opportunity to probe the structure and
composition of the crust. Here, we report on new Chandra observations of Terzan
5 that extend the monitoring to ~2.2 yr into quiescence. We find that the
thermal flux and neutron star temperature have continued to decrease, but
remain significantly above the values that were measured before the 2010
accretion phase. This suggests that the crust has not thermally relaxed yet,
and may continue to cool. Such behavior is difficult to explain within our
current understanding of heating and cooling of transiently accreting neutron
stars. Alternatively, the quiescent emission may have settled at a higher
observed equilibrium level (for the same interior temperature), in which case
the neutron star crust may have fully cooled.