The Mini-Calorimeter on-board AGILE: 18 months in orbit

AGILE, the Italian space mission dedicated to gamma-ray and hard-X astrophysics, was succesfully launched on 23 April 2007 and is currently fully operative. AGILE is placed in an equatorial Low-Earth Orbit, at 550 km altitude with 2.46 degrees inclination. The Mini-Calorimeter (MCAL) on-board AGILE is a scintillation detector made of 30 CsI(Tl) bars with photodiode readout at both ends, arranged in two orthogonal layers, for a total amount of 20 kg of active material, an on-axis geometrical area of 1400 cm² and a thickness of 1.5 radiation lengths. MCAL can work both as a slave of the AGILE Silicon tracker and as an independent detector for gamma-ray burst (GRB) detection in the 300 keV – 200 MeV energy range. If a trigger is issued by a dedicated onboard logic, data are dowloaded in photon-by-photon mode with a time resolution of 2σs allowing complete spectral and timing analysis of the event, limited by counting statistics only. Moreover, 11 band energy spectra with 1 second time resolution (scientific ratemeters) are continuously integrated on-board and sent to telemetry for background monitoring. MCAL is currently one of the three detectors in space with microsecond timing accuracy in the MeV range, with a detection rate of 1 GRB/week. The performance of the instrument after 18 months of in orbit operations will be discussed, as well as the scientific results achieved.