Long-period thermal oscillations in superfluid millisecond pulsars

Abstract

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 (non-superfluid neutron stars or superfluid stars with only modified Urca reactions), this leads to a quasi-steady state in which the star radiates thermal photons for a long time, possibly accounting for the ultraviolet radiation observed from the millisecond pulsar J0437-4715. 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. 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 quasi-steady state, identifying the characteristic times of growing, decaying, and oscillating solutions. For small gaps, the phenomenology is similar to the previously studied cases, in the sense that the solutions quickly converge to a quasi-steady state. For large gaps ($\gtrsim 0.05$ MeV), these solutions become unstable, leading to a limit-cycle behavior of periodicity $\sim 10^{6-7}yr,inwhichthestarishot($T_s\gtrsim 10^5$K)forasmallfractionofthecycle($\sim 5- 20 %$), and cold for a longer time.

(8 pages, 11 figures, accepted version to be published in A&A)

References in corpus (5)

• Extremely high precision VLBI astrometry of PSR J0437-4715 and implications for theories of gravity
• Internal Heating of Old Neutron Stars: Contrasting Different Mechanisms
• Rotochemical heating in millisecond pulsars: modified Urca reactions with uniform Cooper pairing gaps
• Non-equilibrium beta processes in superfluid neutron star cores
• Rotochemical Heating of Neutron Stars: Rigorous Formalism with Electrostatic Potential Perturbations

Cited by in corpus (8)

• Superfluidity in nuclear systems and neutron stars
• The spectrum of the recycled PSR J0437-4715 and its white dwarf companion
• Neutron star radius measurement from the ultraviolet and soft X-ray thermal emission of PSR J0437-4715
• Neutron star deformation due to poloidal-toroidal magnetic fields of arbitrary multipole order: a new analytic approach
• Urca reactions during neutron star inspiral
• Rotochemical heating of millisecond and classical pulsars with anisotropic and density-dependent superfluid gap models
• Interpreting the AXP 1E 2259+586 antiglitch as a change in internal magnetization
• Neutron star heating vs. HST observations