Antoranz Canales, PedroBarrio Uña, Juan AbelContreras González, José LuisFonseca González, María VictoriaLópez Moya, MarcosMiranda Pantoja, José Miguel2023-06-202023-06-202006-06-230036-807510.1126/science.1128177https://hdl.handle.net/20.500.14352/50930© American Association for the Advancement of Science.We thank the Instituto de Astrofísica de Canarias for the excellent working conditions at the Observatory Roque de los Muchachos in La Palma. Supported by the Bundesministerium für Bildung und Forschung and Max-Planck-Gesellschaft (Germany), INFN (Italy), Comisión Interministerial de Ciencia y Tecnología and Ministerio de © American Association for the Advancement of Science. Educación y Ciencia grant AYA2004-07171-C02-01 (Spain), ETH (Switzerland) research grant TH-34/04-3, and Ministerstwo Nauki i Informatyzacji (Poland) grant 1P03D01028.Microquasars are binary star systems with relativistic radio-emitting jets. They are potential sources of cosmic rays and can be used to elucidate the physics of relativistic jets. We report the detection of variable gamma-ray emission above 100 gigaelectron volts from the microquasar LSI+61 303. Six orbital cycles were recorded. Several detections occur at a similar orbital phase, which suggests that the emission is periodic. The strongest gamma-ray emission is not observed when the two stars are closest to one another, implying a strong orbital modulation of the emission or absorption processes.engjournal articlehttp://dx.doi.org/10.1126/science.1128177http://www.sciencemag.orghttp://arxiv.org/abs/astro-ph/0605549open access537539.1LS-I +61-Degrees-303Source 2CG 135+01X-RayStar LSI+61-Degrees-303Light-CurveBinaryI+61-Degrees-303LS-I+61-303ParametersDiscovery.Electrónica (Física)ElectricidadFísica nuclear2202.03 Electricidad2207 Física Atómica y Nuclear