Analytic Core Envelope Models for the Crab and the Vela Pulsars

TL;DR

This study uses analytic core-envelope models to estimate the mass and surface redshift of the Crab and Vela pulsars, aligning predictions with observational data and suggesting potential detection of gravitationally redshifted electron-positron annihilation lines.

Contribution

It introduces refined core-envelope models for pulsars that incorporate recent observational constraints to estimate their physical parameters.

Findings

Estimated mass of Crab pulsar: 1.79-1.88 solar masses

Predicted surface redshift: 0.374-0.393

Electron-positron annihilation line energy around 0.40 MeV

Abstract

We study analytic core-envelope models obtained in Negi et al. (1989) under slow rotation. We have regarded in the present study, the lower bound on the estimate of moment of inertia of the Crab pulsar, $I_{\rm Crab,45} \geq 2$ (where $I_{45}=I/10^{45}\rm g{cm}^2$) obtained by Gunn and Ostriker (1969) as a round off value of the recently estimated value of $I_{\rm Crab,45} \geq 1.93$ (Bejger \& Haensel 2003) for the Crab pulsar. If this value of lower bound is combined with the other observational constraint obtained for the Crab pulsar (Crawford \& Demiansky 2003), $G_h = I_{\rm core}/I_{\rm total} \geq 0.7$ ( where $G_h$ is called the glitch healing parameter and represents the fractional moment of inertia of the core component in the starquake mechanism of glitch generation), the models yield the mass, $M$, and surface redshift, $z_a$, for the Crab pulsar in the range, $M = 1.79M_\odot - 1.88M_\odot$; $z_a = 0.374 - 0.393$ ($I_{45} = 2$) for an assigned value of the surface density, $E_a = 2\times 10^{14}\rm g{cm}^{-3}$ (like, Brecher and Caporaso 1976). This assigned value of surface density, in fact, is an outcome of the first observational constraint imposed on our models that further yields the mass $M = 1.96M_\odot $ and surface redshift $z_a=$ 0.414 ($I_{45}= 2$) for the values of $G_h \approx 0.12$, which actually belongs to the observed `central' weighted mean value for the Vela pulsar. These values of mass and surface redshift predict the energy of a gravitationally redshifted electron-positron annihilation line, $E (\rm {MeV}) = 0.511/(1+z_a)$ (Lindblom 1984) in the range about 0.396 - 401 MeV from the Crab and about 0.389 MeV from the Vela pulsar. The evidence of a line feature at about 0.40MeV from the Crab pulsar (Leventhal et al. 1977) agrees quite well with the finding of this study.