HEAD Division Meeting 1999, April 1999
Session 15. X-Ray Binaries
Poster, Tuesday, April 13, 1999, 8:30am-6:02pm, Gold Room

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[15.14] Outbursts from 4U 1145--619: A Transient X-ray Pulsar

Colleen A. Wilson (NASA/MSFC), Mark H. Finger, D. Matthew Scott (USRA/MSFC)

4U 1145--619, a 293 second Be/X-ray pulsar, was discovered with {\em Uhuru}(Forman et al. 1978, ApJS, 38, 357) and first identified as a pulsar in 1977 with {\em Ariel V} (White et al. 1978, Nature, 274, 664). From 1991 to 1998, BATSE observed 4U 1145--619 in a series of 12 periodic outbursts, each with durations of 8-30 days. Combining these data with previously published results yielded an outburst ephemeris of T\rm out = {\rm MJD} 48871.6(±0.6) ± 186.68(±0.05) E\rm out, where T\rm out is the time of peak intensity and E\rm out is the cycle number. Most outbursts occur within phases ±0.1 of the outburst ephemeris. Pulse frequency measurements were consistent with a long-term average frequency derivative of \dot \nu = -3 \times 10-14 Hz s-1. Most outbursts reached peak total fluxes of \lesssim 100 mCrab (20-50 keV) and had 20-50 keV r.m.s. pulse fractions of about 30%. (A pulse fraction of 70% was observed for one outburst). Two outbursts reached 20-50 keV peak total fluxes of 550 mCrab, but had very different 20-50 keV pulse fractions of about 30% and about 50%. Three outbursts with peak total fluxes of 120, 134, and 180 mCrab, had r.m.s. pulse fractions of about 28%, 34%, and 52%. During the brightest 3 outbursts observed with BATSE, the pulse frequency increased. Fainter outbursts observed with BATSE appeared to reach peak intensity at a later phase (relative to the ephemeris) than brighter outbursts, and were typically not detectable at the expected times of peak intensity. The pulse profile showed significant intensity and energy dependent pulse shape variations. We present histories of pulse frequency, 20-50 keV intensity, and pulse profiles.


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