1 Introduction

The gamma-ray mission AGILE (Astro-rivelatore Gamma a Immagini LEggero) was proposed in 1997 to the Italian Space Agency (ASI) Program of Small Scientific Missions ([Tavani et al. 1999a]). AGILE is a light and cost-effective mission ($\sim 60$ kg instrument, $\le 200$ kg in total) optimized for gamma-ray imaging and fast timing detection. Gamma-ray imaging in the energy range $30~{\rm MeV} - 50~{\rm GeV}$ is based on silicon tracking detectors developed for space missions by INFN and Italian University laboratories during the past years ([Barbiellini et al. 1995]; [Morselli et al. 1995]). AGILE's field of view (FOV) is unprecedently large ($\ge 1/5$ of the whole sky) because of state-of-the-art readout electronics and segmented anticoincidence system. The baseline instrument is designed to achieve an on-axis sensitivity comparable to that of EGRET on board of CGRO (a smaller background resulting from an improved angular resolution more than compensates the loss due to a smaller effective area) and a better sensitivity for large off-axis angles (up to $\sim 60^{\circ}$). Planned to be operational during the year 2002 for a 3-year mission, AGILE will ideally "fill the gap'' between EGRET and GLAST.

Figure 1 shows a lateral view of the baseline instrument. Spectral information ($\Delta \, E/E \sim 1$)is obtained by multiple scattering of created pairs in tungsten-silicon planes (for energies less than $\sim 500$ MeV) and by the use of a mini-calorimeter (e.g., [Morselli et al. 1999]). The Super-AGILE option is based on an additional ultra-light coded-mask imaging system positioned on top of the baseline instrument. An additional silicon plane detector is planned to be sensitive in the energy band $\sim 10 - 40~{\rm keV}$.The imaging capability of Super-AGILE is designed to provide $\sim 1-2$ arcmin positions for GRBs.

  

Figure 1: Lateral cross-section of the AGILE baseline instrument. The anticoincidence system of plastic scintillator panels surrounds the detector made of 10 W-Si planes ($0.7 \, X_{\rm o}$)plus 2 more Si-only planes and a CsI mini-calorimeter ($1.5 \, X_{\rm o}$). The baseline payload size is $\sim 53 \times 53 \times 35 \rm \, cm^3$,and $\sim 53 \times 53 \times 44 \rm \, cm^3$ for Super-AGILE

  

Figure2: Effective area at 1 GeV as a function of photon incidence angle for AGILE ([Tavani et al. 1999b]) and EGRET ([Thompson et al. 1993])