Longperiod thermal oscillations in superfluid millisecond pulsars
Abstract
Context. In previous papers, we have shown that, as the rotation of a neutron star slows down, it will be internally heated as a consequence of the progressively changing mix of particles (rotochemical heating). In previously studied cases (nonsuperfluid neutron stars or superfluid stars with only modified Urca reactions), this leads to a quasisteady state in which the star radiates thermal photons for a long time, possibly accounting for the ultraviolet radiation observed from the millisecond pulsar J04374715.
Aims: For the first time, we explore the phenomenology of rotochemical heating with direct Urca reactions and uniform and isotropic superfluid energy gaps of different sizes.
Methods: We first do exploratory work by integrating the thermal and chemical evolution equations numerically for different energy gaps, which uncovers a rich phenomenology of stable and unstable solutions. To understand these, we perform a stability analysis around the quasisteady state, identifying the characteristic times of growing, decaying, and oscillating solutions.
Results: For small gaps, the phenomenology is similar to the previously studied cases, in the sense that the solutions quickly converge to a quasisteady state. For large gaps ( ≳ 0.05 MeV), these solutions become unstable, leading to a limitcycle behavior of periodicity ~10^{67} yr, in which the star is hot (T_{s} ≳ 10^{5} K) for a small fraction of the cycle (~520%), and cold for a longer time.
 Publication:

Astronomy and Astrophysics
 Pub Date:
 April 2011
 DOI:
 10.1051/00046361/201015603
 arXiv:
 arXiv:1008.3013
 Bibcode:
 2011A&A...528A..66P
 Keywords:

 stars: neutron;
 dense matter;
 stars: rotation;
 pulsars: general;
 pulsars: individual: PSR J04374715;
 Astrophysics  High Energy Astrophysical Phenomena;
 Astrophysics  Solar and Stellar Astrophysics;
 Condensed Matter  Superconductivity
 EPrint:
 (8 pages, 11 figures, accepted version to be published in A&