(65803) 1996 GT

P. Pravec, Ondrejov Observatory; L. A. M. Benner, Jet Propulsion Laboratory (JPL); M. C. Nolan, National Astronomy and Ionosphere Center; P. Kusnirak, Ondrejov Observatory; D. Pray, Greene, RI, U.S.A.; J. D. Giorgini, R. F. Jurgens, and S. J. Ostro, JPL; J.-L. Margot, University of California, Los Angeles; C. Magri, University of Maine at Farmington; A. Grauer, University of Arkansas at Little Rock; and S. Larson, University of Arizona, report that photometric observations -- obtained during Nov. 20-24 at Ondrejov, at Steward Observatory, and by Pray -- show that (65803) is a binary system with an orbital period of 11.9 hr. The primary rotates with a period of 2.26 hr, and its lightcurve amplitude of 0.10 mag is indicative of a nearly spheroidal shape. Mutual eclipse/occultation events 0.05-0.08 mag deep indicate a secondary-to-primary mean-diameter ratio of 0.2. Arecibo radar delay-Doppler images (2380 MHz, 12.6 cm) obtained on Nov. 23 and 24 independently confirm that (65803) is a binary system. Preliminary estimates of the diameters, based on images at 15-m resolution, are approximately 800 and approximately 150 m.