HARD X-RAY AND IR OBSERVATIONS OF CYGNUS-X-3

In 1994 June-July we obtained nearly concurrent measurements of Cyg X- 3 in hard X-rays and the infrared, using the OSSE instrument on GRO an d the UKIRT. OSSE made a high significance measurement of the hard X-r ay (> 50 keV) orbital light curve. Five days after the end of the OSSE observations we obtained a good IR K-band Light curve from data cover ing one orbit of Cyg X-3. Measurements of the light curve phase and sh ape probe the geometry of the system and the physics of radiation prod uction and scattering. We determined for the first time that the light curve phases are consistent at these two different wavelengths. The l ight curve shapes were both marginally inconsistent (at about the 0.2% level) with the canonical soft X-ray shape measured by EXOSAT in 1983 -1985. Underlying variations in DC IR flux and flaring during the obse rvation make it difficult to draw unambiguous conclusions; more observ ations, with better IR coverage, are needed.