Detailed Analysis of the Pulsations during and after Bursts from the Bursting Pulsar (GRO J1744–28)

The hard X-ray bursts observed during both major outbursts of the Bursting Pulsar (GRO J1744-28) show pulsations near the neutron star spin frequency with an enhanced amplitude relative to that of the persistent emission. Consistent with previous work, we find that the pulsations within bursts lag behind their expected arrival times based upon the persistent pulsar ephemeris. For an ensemble of 1293 bursts recorded with the Burst and Transient Source Experiment, the average burst pulse time delay (ΔtFWHM) is 61.0 ± 0.8 ms in the 25-50 keV energy range and 72 ± 5 ms in the 50-100 keV band. The residual time delay (Δtresid) from 10 to 240 s following the start of the burst is 18.1 ± 0.7 ms (25-50 keV). A significant correlation of the average burst time delay with burst peak flux is found. Our results are consistent with the model of the pulse time lags presented by Miller.