THE NATURE OF THE FLUCTUATIONS PRECEDING THE GIANT BURSTS IN THE BURSTING PULSAR GRO J1744-28

We examine recent time-dependent accretion disk calculations by Canniz zo that attempt to reproduce the giant bursts in GRO J1744-28 and find that the fluctuations that precede the main burst resemble the fluctu ations that were observed in GRO J1744-28 toward the end of the time d uring which the giant bursts were seen. The calculations by Cannizzo w ere tuned to be at a rate of accretion slightly greater than the criti cal rate M-crit that divides steady and bursting behavior. This tuning leads to a near balance between the heating and cooling rates within the accretion disk such that oscillations slowly develop and grow, eve ntually becoming unbounded and producing a global instability. The fac t that an increase in the amplitude of the interburst oscillations was seen in GRO J1744-28 most strongly during the late epoch of the time of several months covering the giant bursts is consistent with the mas s accretion rate onto the pulsar decreasing and approaching M-crit.