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[81.05] The 2003 Outburst of the Black Hole Binary V4641 Sgr (=SAX 1819.3-2525)

C. D. Bailyn, D. Maitra, M. Buxton (Yale University), A. Chen (National Cheng-Kung University, Taiwan)

V4641 Sgr is a binary system consisting of a black hole and a Roche-lobe filling B star (Orosz et al. 2002 ApJ 568, 845). The system is an X-ray transient, and underwent a short outburst in August 2003. We report X-ray, optical and IR observations of this outburst. The X-ray lightcurve shows flares of >100 mCrab on timescales as short as 1 second. The optical/IR lightcurve is also highly variable. Simultaneous optical/X-ray observations show strong correlations, with the optical somewhat delayed and smoothed compared to the X-ray. This behavior can be explained if the optical emission comes from X-rays reprocessed by the accretion disk.

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Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.