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

Abstract

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 period near 1 March 1996. We also present improved estimates of the peak luminosity during bursts.