Keith M. Jahoda

Peak luminosities of bursts from GRO J1744-28 measured with the RXTE PCA; Italia: wij post 17 two 4s — a one man marching band — got darn brigth

GRO J1744-28, discovered by BATSE in December 95, is the second neutron star system known to produce frequent accretion powered bursts. The system has been regularly monitored with the RXTE PCA since the peak of the first outburst in January 96 at which time the observed persistent and bursting count rates were ~25,000 ct/sec and ~150,000 ct/sec, with corresponding instrumental deadtimes of ~10% and > 50%. We present a model which allows the reconstruction of the true incident count rate in the presence of enormous deadtime and use the model to derive a history of the peak luminosities and fluences of the bursts as a function of time. During the peak of the January 1996 and January 1997 outbursts, when the persistent emission was > 1 Crab, we infer peak luminosities of ~100 times the Eddington luminosity, and a ratio of persistent emission to integrated burst emission of ~34.

Determination of peak fluxes and α for bursts from GRO J1744-28

The Rossi X-ray Timing Explorer (RXTE) has been monitoring the Bursting Pulsar, GRO J1744-28, since Jan. 1996. Large deadtimes in the proportional counter array (PCA) have made measurements of the peak flux during bursts problematic, therefore the value α, of the ratio of time averaged persistent luminosity to time averaged burst luminosity, has not been well determined. The value of α has important implications for understanding the nature of the bursts. Some RXTE observations begun after the recent reemergence of GRO J1744-28 in Dec. 1996 were performed with the source offset from the axis of peak PCA response. This reduces the deadtime in the PCA and allows a more precise determination of burst peak fluxes and thus α. These observations provide an understanding of the deadtime processes during periods when the source was viewed at peak response. Between 17–24 January 1997 we estimate that α was ≈34. Based on similarity of the overall lightcurve and countrate, this value is also appropriate for the peri...