Hard X - Ray Spectroscopy and Pulsar Phase Analysis ofthe

We report OSSE observations of the bursting X-ray pulsar GRO J1744{28 made in December 1995 and January 1996 at hard X-ray energies > 35 keV. The pulse proole of the persistent (i.e. non-bursting) pulsar emission is t with a sinusoid in the energy range 35{90 keV. Residuals reveal a second harmonic amplitude of 3:0 0:5% of the fundamental. The distribution of time intervals between bursts measured in January is characterized by a broad at-topped function with width ' 35 min and mean ' 33 min. The burst proole averaged over an ensemble of 104 bursts in the 35{60 keV energy range has FWHM width of 3:6 0:3 s and displays a factor of 2 faster rise time than decay and a pronounced dip in persistent emission after the burst. The phase of the sinusoidal pulse proole during bursts lags the phase prior to bursts by ' 90 ms (' 1:2 radians), and a 29 6 ms (0:39 0:08 radians) lag persists following the burst. There are no statistically signiicant spectral diierences between the hard X-ray spectra of the bursting and persistent emission in the OSSE energy range, nor is there any evidence of annihilation or neutron capture line emission or cyclotron absorption.