Ab. Giles et al., THE MAIN CHARACTERISTICS OF GRO J1744-28 OBSERVED BY THE PROPORTIONALCOUNTER ARRAY EXPERIMENT ON THE ROSSI X-RAY TIMING EXPLORER, The Astrophysical journal, 469(1), 1996, pp. 25-28
In this Letter, we provide an introduction to the main features seen i
n a series of observations of the bursting pulsar GRO J1744-28. The ob
servations were made from 1996 January through May with the proportion
al counter array on the Rossi X-Ray Timing Explorer spacecraft. In the
2-10 keV band, GRO J1744-28 emitted large bursts of similar to 10 s d
uration at a rate of about 2 per hour. The peak flux during these burs
ts was similar to 6-40 times greater than that in the quiescent, or no
nbursting, periods. For the earliest bursts, the inferred peak luminos
ity approaches 100 times the Eddington limit, which is suggestive of s
ome kind of beaming mechanism. A range of smaller bursts and quasi-per
iodic oscillation features were also seen. All this activity was super
posed on an almost perfect sinusoidal modulation at a frequency of 2.1
4 Hz with an amplitude of similar to 10% of the nonbursting flux. The
source's persistent flux declined in a roughly linear trend from late
January until mid-May, by which time its intensity was confused with s
everal other sources.