On the Angular Resolution of the AGILE gamma-ray imaging det ector

We present a study of the Angular Resolution of the AGILE gamma-ray imaging detector (GRID) that is operational in space since April 200 7. The AGILE instrument is made of an array of 12 planes each equipped with a Tungsten c onverter and Silicon microstrip detectors and is sensitive in the energy range 50 MeV - 10 GeV. Among the space instruments devoted to gamma-ray astrophysics, AGILE uniquely exploits an analog readout system with dedicated electronics couple d with Silicon detectors. We show the results of Monte Carlo simulations carried out to reproduce the gamma- ray detection by the GRID , and we compare them to in-flight data. We use the Crab (pulsar + Nebula) system for discussion of real data performance, sin ce its E − 2 energy spectrum is representative of the majority of gamma-ray sou rces. For Crab-like spec- trum sources, the GRID angular resolution (FWHM of ∼ 4 ◦ at 100 MeV; ∼ 0 . 8 ◦ at 1 GeV; ∼ 0 . 9 ◦ integrating the full energy band from 100 MeV to tens of GeV) i s stable across a large field of view, being characterized by a flat resp onse up to 30 ◦ o ff -axis. A comparison of the angular resolution obtained by the two op erational gamma-ray instruments, AGILE-GRID and Fermi-LAT , is interesting in view of future gamma-ray missions, that are currently under study. The two instrumen ts exploit di ff erent detector configurations a ff ecting the angular resolution: the former being optimized i n the read- out and track reconstruction especially in the low-energy b and, the latter in terms of converter thickness and power consumption. We show that, de spite these di ff erences, the angular resolution of both instruments is very similar b etween 100 MeV and a few GeV