ON THE NATURE OF THE BURSTING X-RAY PULSAR GRO J1744-28

The unusual properties of the bursting X-ray pulsar GRO J1744-28 are e xplained in terms of a low-mass X-ray binary system consisting of an e volved stellar companion transferring mass through Roche-lobe overflow onto a neutron star, implying that the inclination of the system is l ess than or similar to 18 degrees. Interpretation of the QPO at freque ncy nu(QPO) = 40 Hz using the beat-frequency model of Alpar & Shaham a nd the measured period derivative P with the Ghosh & Lamb accretion-to rque model implies that the persistent X-ray luminosity of the source is approximately equal to the Eddington luminosity and that the neutro n star has a surface equatorial magnetic field B-eq congruent to 2 x 1 0(10) (nu(QPO)/40 Hz)(-1) G for standard neutron star parameters. This implies a distance to GRO J1744 -28 of congruent to 5 (nu(QPO)/40 Hz) (1/6)b(1/2) kpc, where b < 1 is a correction factor that depends on th e orientation of the neutron star.