THE NATURE OF THE GIANT OUTBURSTS IN THE BURSTING PULSAR GRO J1744-28

We investigate the possible role of an accretion disk instability in p roducing the giant outbursts seen in GRO J1744-28. Specifically, we st udy the global, time-dependent evolution of the Lightman-Eardley insta bility, which can develop near the inner edge of an accretion disk whe n the radiation pressure becomes comparable to the gas pressure. Broad ly speaking, our results are compatible with earlier works try Taam & Lin and by Lasota & Pelat. The uniqueness of GRO J1744-28 appears to b e associated with the constraint that, in order for outbursts to occur , the rate of accretion at the inner edge must be within a narrow rang e just above the critical accretion rate at which radiation pressure i s beginning to become significant.