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Session 110 - X-ray, Binaries & Accretion Disks.
Display session, Saturday, January 10
LMC X--1 was observed with the Rossi X-ray Timing Explorer (RXTE) over a nine-month interval to search for low-frequency quasi-periodic oscillations (QPO) which had been previously seen in one Ginga observation (Ebisawa et al.\ PASJ 41, 519, 1989). Power-density spectra in the range 0.001--1.0 Hz for each of the nine \sim5-ks observations show no evidence of QPO near 0.075 Hz (with a 3\sigma upper limit of <0.9% r.m.s.\ variation). However, the hardness ratio (5.9--15.9 keV/2--5.9 keV) is strongly correlated with an increase in high-energy count rate. Additionally, the very low-frequency noise shows a weak correlation with source hardness. Individual observations reveal that LMC X--1 undergoes short time-scale (\sim5 min) variability at both low and high energies, with the high-energy light curve lagging by _ <\atop^\sim0.02 s. The overall RXTE light curve shows no significant periodicity near the \sim4.2-day spectroscopic period nor in the range 0.5--20.0 days. Spectral modeling reveals no change in the temperature of the soft (blackbody) component or the slope of the hard (power-law) component. The slope of the high-energy tail is steeper than in other studies (e.g.\ Ebisawa et al.\ 1989; Schlegel et al.\ ApJ 422, 243, 1994), but there is some uncertainty in the calibration of RXTE at low energies.
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