AAS 201st Meeting, January, 2003
Session 15. Black Holes Observed and Modeled
Poster, Monday, January 6, 2003, 9:20am-6:30pm, Exhibit Hall AB

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[15.01U] The Ups and Downs of the Black Hole Binary Cygnus X-1: Correlations of the X-ray High/Low Energy States with the Optical Light Curves

E.G. Barron, J.A. Urban, E.F. Guinan (Villanova University), J.F. Sepinsky (University of Delaware), I. Ribas (Universidad de Barcelona)

Cygnus X-1 is one of the best observed stellar black hole X-ray binaries. This 9th mag binary consists of an O9.7 Iab star and a (black hole + disk) companion. Its orbit is nearly circular and the system has a period of P = 5.6 days. At optical wavelengths Cyg X-1 shows complicated low-amplitude periodic light variations arising primarily from the tidal distortion of the O-supergiant.

We have been carrying out photoelectric photometry of Cyg X-1 over the last three years. This photometry is being conducted with the Four College 0.8m robotic telescope located in southern Arizona and the 38-cm telescope at Villanova University. The observations are being made using UBV and Strömgren filters and a set of H\alpha intermediate and narrow band filters. The optical light curves show changes in shape and light amplitudes on time scales of weeks to months. Of particular interest is the investigation of the correlation of the characterisitics of the light variations with X-ray observations being made contemporaneously with the Rossi X-Ray Timing Explorer (RXTE) All Sky Monitor (ASM: 1.5-12 keV) satellite. RXTE observations of Cyg X-1 reveal that the star was mostly in a low X-ray state since its last sustained (soft X-ray) outburst during 1996. However, during September 2001 the star has moved into an X-ray high state and remained high since then. In this poster we discuss the characteristics of the light curve during high and low X-ray states. Modeling of the light curves have been carried out to extract information about O-star, the accretion disk, and black hole during widely different energy states of the system.

We are grateful for the support from NSF/RUI Grant AST 00-71260 and the Undergraduate Summer Research Assistance Program Grant from the Delaware Space Consortium.

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