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M.B. Larson, B. Link (Montana State U.)
The recent temperature measurements of the two older isolated neutron stars PSR 1929+10 and PSR 0950+08 indicate that these objects are heated. A promising candidate heat source is friction arising from differential rotation between the stellar crust and the neutron superfluid it contains. We show that differential rotation velocities of ~1 rad s-1 would account for the observed temperatures; such differential rotation could be sustained by pinning of superfluid vortices to the inner crust lattice with strengths of ~ 1 MeV per nucleus. Pinned vortices creep outward through thermal fluctuations or quantum tunneling. For thermally-activated creep, the coupling between the superfluid and crust is highly sensitive to temperature. Under some circumstances, a feedback instability could occur in stars younger than ~105 yr causing oscillations of the temperature and spin-down rate over a timescale of ~0.3 tage. For stars older than ~106 yr, however, vortex creep probably occurs through quantum tunneling, and the creep velocity is too insensitive to temperature for the instability to occur. These older stars could still be heated through steady frictional heat generation.
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