Masses, radii, and magnetic fields of pulsating X-ray sources - Is the 'standard' model self-consistent

Prototype calculations for Her X-1 and 4U 0115 + 63 designed to test the 'standard' model of a pulsating X-ray source for self-consistency are presented. 'Semiempirical' mass-radius (M-R) relations for these two X-ray pulsars based on observational data (luminosities, pulse periods, spin-up rates, cyclotron spectral features) and their theoretical interpretation are constructed in terms of the MHD accretion torque theory of Ghosh and Lamb (1979). It is noted that these semiempirical M-R relations depend only on physical processes occurring exterior to an accreting neutron star. These are compared with theoretical M-R relations derived by integrating the hydrostatic equilibrium (Oppenheimer-Volkoff) equation for representative equations of state that might characterize the condensed matter in a neutron star's interior. In general terms, the results support the 'fast rotator', dipolar, accreting neutron star model for both Her X-1 and 4U 0115 + 63.