Model-independent constraints on superfluidity from the cooling neutron star in Cassiopeia A

Abstract

We present a new model-independent (applicable for a broad range of equations of state) analysis of the neutrino emissivity due to triplet neutron pairing in neutron star cores. We find that the integrated neutrino luminosity of the Cooper Pair Formation (CPF) process can be written as a product of two factors. The first factor depends on the neutron star mass, radius and maximal critical temperature of neutron pairing in the core, $T_{Cn\max }$, but not on the particular superfluidity model; it can be expressed by an analytical formula valid for many nucleon equations of state. The second factor depends on the shape of the critical temperature profile within the star, the ratio of the temperature $T$ to $T_{Cn\max }$, but not on the maximal critical temperature itself. While this second factor depends on the superfluidity model, it obeys several model-independent constraints. This property allows one to analyse the thermal evolution of neutron stars with superfluid cores without relying on a specific model of their interiors. The constructed expressions allow us to perform a self-consistent analysis of spectral data and neutron star cooling theory. We apply these findings to the cooling neutron star in the Cassiopeia A supernova remnant using 14 sets of observations taken over 19 years. We constrain $T_{Cn\max }$ to the range of $(5-10)\times 10^8$ K. This value depends weakly on the equation of state and superfluidity model, and will not change much if cooling is slower than the current data suggest. We also constrain the overall efficiency of the CPF neutrino luminosity.

18 pages, 14 figures, 6 tables; accepted for publication in MNRAS

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• Baryonic models of ultra-low-mass compact stars for the central compact object in HESS J1731-347
• Dark gauge boson production from neutron stars via nucleon-nucleon bremsstrahlung
• Dynamical tides in superfluid neutron stars
• Long-lasting accretion-powered chemical heating of millisecond pulsars
• Bayesian inferences on covariant density functionals from multimessenger astrophysical data: Nucleonic models
• Hybrid cooling of the Cassiopeia A neutron star
• Probing Strong Field $f(R)$ Gravity and Ultra-Dense Matter with the Structure and Thermal Evolution of Neutron Stars
• Delayed Thermal Relaxation of Rapidly Cooling Neutron Stars: Nucleon Superfluidity and Non-nucleon Particles
• Constraints on the internal physics of neutron stars from the observational data of several young pulsars: the role of a power-law decaying dipole magnetic field
• Axion Emission from Proton Cooper Pairs in Neutron Stars
• Dissipative superfluid relativistic magnetohydrodynamics of a multicomponent fluid: the combined effect of particle diffusion and vortices