The AGILE gamma ray satellite: the construction and performance of the silicon tracker

AGILE (light imager for gamma-ray astrophysics) is a gamma ray satellite for observation in the energy range 30 MeV-50 GeV, that will he launched in a low equatorial orbit with PSLV (India) in 2005 and is characterized by light weight (100 kg for the scientific instrument), a large field of view (1/4 of the sky), low dead time (100 μs) and excellent background rejection. AGILE is made of a silicon-tungsten tracker, a CsI minicalorimeter, an anticoincidence system of segmented plastic scintillators and an X-ray imaging detector sensitive in the 15-45 keV range. The silicon tracker consists of 12 planes, each of them made of two layers of 16 single-sided, AC coupled, 410 μm thick, 9.5×9.5 cm² silicon detectors with a readout pitch of 242 μm and a floating strip. The readout ASIC is the TAA1, an analog-digital, low noise, self triggering ASIC used in a very low power configuration (<400 μW/channel) with full analog readout. The trigger of the satellite is given by the tracker itself. The total number of readout channels is around 37000. We present a detailed description of the tracker, its trigger and readout logic, its assembly procedures and some experimental results obtained on dedicated particle and photon test beams with a small scale prototype.