A starquake model for the Vela pulsar.

The measured values of the glitch healing parameter, Q, of the Vela pulsar are found to be inconsistent with the starquake mechanism for glitch generation in various neutron star (NS) models, based upon the parametrized equations of state (EOSs) of dense nuclear matter. Such models correspond to an unrealistic mass range ≤0.5 M⊙ for the pulsar, if the observational constraints of the fractional moment of inertia of the core component which is called the glitch healing parameter, Q, according to the starquake model, are imposed on these models. However, we show that these observational constraints yield a realistic mass range for NS models, corresponding to a core given by the stiffest equation of state, d P/d E= 1 (in geometrized units), and the envelope is characterized by the well-known EOS of an adiabatic polytrope , if the continuity of the adiabatic speed of sound , together with the pressure ( P), the energy density ( E) and the two metric parameters (ν and λ), is assured at the core–envelope boundary of the models and this boundary is worked out on the basis of the ‘compatibility criterion’ for hydrostatic equilibrium. The models yield a stable sequence of NS masses in the range 1.758 ≤ M≤ 2.2 M⊙, corresponding to the glitch healing parameter range 0 ≤ Q≤ 0.197, for a choice of the ‘transition density’ at the core–envelope boundary. The maximum stable value of 2.2 M⊙ in this sequence, in fact, corresponds to the lowest possible upper bound on NS masses calculated in the literature, on the basis of modern EOSs for NS matter. The models yield the surface redshift and mass M≃ 2.153 M⊙ for the ‘central’ weighted mean value, Q= 0.12 ± 0.07, of the glitch healing parameter of the Vela pulsar. This value of mass can increase slightly up to M≃ 2.196 M⊙, whereas the surface redshift can increase up to the value [which represents an ultracompact object ], if the observational constraint of the upper weighted mean value of Q≃ 0.19 is imposed on these models. However, for the lower weighted mean value of Q≃ 0.05, the mass and surface redshift can decrease to the values of zR≃ 0.6066 and M≃ 2.052 M⊙ respectively. These results set the lower bound on the energy of gravitationally redshifted radiation in the rather narrow range of 0.291–0.302 MeV. The observation of the lower bound on the energy of a γ-ray pulse at about 0.30 MeV from the Vela pulsar in 1984 is in excellent agreement with this result, provided that this energy can be interpreted as the energy of gravitationally redshifted electron–positron annihilation radiation from the surface of the star. [ABSTRACT FROM AUTHOR]