The high mass x-ray binary LSI +61 303 was observed for several months in 2006 and 2007 by VERITAS, an array of several imaging Cherenkov telescopes located at the Fred Lawrence Whipple Observatory in southern Arizona. The unusual system of a black hole or neutron star orbiting a Be star proves to be an efficient particle accelerator. Here we present the detection of LSI +61 303 in very high energy gamma-rays during several orbital cycles. The high sensitivity of VERITAS allows the determination of fluxes and energy spectra at different phases of the orbit, revealing the high flux variability of this interesting source.

VERITAS

Proceedings of the 30th International Cosmic Ray Conference; Rogelio Caballero, Juan Carlos D'Olivo, Gustavo Medina-Tanco, Lukas Nellen, Federico A. Sánchez, José F. Valdés-Galicia (eds.); Universidad Nacional Autónoma de México, Mexico City, Mexico, 2008; Vol. 2 (OG part 1), pages 747-750