AAS 198th Meeting, June 2001
Session 10. Black Holes
Display, Monday, June 4, 2001, 9:20am-6:30pm, Exhibit Hall

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[10.04] X-Ray and UV Orbital Phase Dependence in LMC X-3

J. F. Dolan (Lab. Astron. & Solar Phys., NASA GSFC), P. T. Boyd, A. P. Smale (Lab. High Energy Astrophys., NASA GSFC)

The black-hole binary LMC X-3 is known to be variable on time scales of days to years. We investigated X-ray and ultraviolet variability in the system as a function of the 1.7 d binary orbit using a 6.4 day observation with the Rossi X-ray Timing Explorer (RXTE) in 1998 December. An abrupt 14 % flux decrease lasting nearly an entire orbit was followed by a return to previous flux levels. This behavior occurred twice at nearly the same binary phase, but is not present in consecutive orbits. When the X-ray flux is at lower intensity, a periodic amplitude modulation of 7 % is evident in data folded modulo the orbital period. The higher intensity data show weaker correlation with phase. This is the first report of X-ray variability at the orbital period of LMC X-3. Archival RXTE observations of LMC X-3 during a high flux state in 1996 December show similar phase dependence. An ultraviolet light curve obtained with the High Speed Photometer (HSP) on the Hubble Space Telescope (HST) shows a phase dependent variability consistent with that observed in the visible, ascribed to the ellipsoidal variation of the visible star.

The X-ray spectrum of LMC X-3 is acceptably represented by a phenomenological disk black-body plus a power law. Changes in the spectrum of LMX X-3 during our observations are compatible with earlier observations during which variations in the 2-10 keV flux are closely correlated with the disk geometry spectral model parameter.

The author(s) of this abstract have provided an email address for comments about the abstract: tejfd@splvin.gsfc.nasa.gov

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