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Session 12 - Degenerate Stars & Supernovae.
Oral session, Monday, June 09
North Main Hall C/D,
During the 1996 outburst of the Bursting Pulsar, GRO J1744-28, we observed a delay of 50ms in the arrival time of the pulsar signal during each of the many X-ray bursts. We also observed a phase delay of 25ms which persists after each burst and decays exponentially over the several hundred to a few thousand seconds until the next burst. While we observed a pulse phase delay during the bursts, saturation effects in the Proportional Counter Array on the Rossi X-ray Timing Explorer prevented a detailed study of the evolution of the delay throughout the bursts. The observation of a second outburst from the Bursting Pulsar in 1997 has provided the opportunity to overcome the limitations of our earlier data. We have now made a more detailed study of the evolution of the pulsar phase delay taking advantage of offset pointing and better data collection. We observe that the pulse arrival time evolves continuously throughout the bursts while the pulse shape remains almost completely sinusoidal. This phenomenon has been explained as the result of either changes in the accretion flow or motion of the crust of the neutron star though neither of these explanations agrees satisfactorily with the observation. The continuity of the evolution and the persistence of the phase delay make explanations involving angular momentum of some component of the pulsar system compelling.
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