AGILE

Collaboration:

• Agenzia Spaziale Italiana
• IAS (CNR) - Roma Rome, Italy (E. Costa, L. Barbanera, G. Di Persio,M. Feroci, M. Frutti, I. Lapshov, B. Martino, M. Mastropietro, E. Morelli,M. Rapisarda, A. Rubini, P. Soffitta)
• IFCTR (CNR) - Milano, Milano, Italy (M. Tavani, A. Argan, A. Bernabeo,P. Caraveo, A. Chen, M. Conte, G. De Paris, L. Soli, C. Mangili, S. Mereghetti, F. Perotti, E. Rotta, S. Vercellone)
• INFN Roma 1, Rome, Italy (P. Lipari, D. Zanello)
• INFN Roma 2, Rome, Italy (A. Morselli, V. Cocco, P. Picozza, C. Pittori)
• University and INFN Trieste, Trieste, Italy (G. Barbiellini, V. Bologna, G. Bordignon, G. Fedel, F. Liello, F. Longo, C. Pontoni, M. Prest, E. Vallazza)
• TESRE (CNR) - Bologna, Bologna, Italy (G. Di Cocco, N. Auricchio, G. Ferro, M. Galli, F. Gianotti, C. Labanti, A. Mauri, E. Rossi, M. Schiavone, J. Stephen, A. Traci, M. Trifoglio)

1. Goal of the experiment

Gamma-rays of cosmic origin are a manifestation of the most energetic phenomena in our Universe. A large variety of sources emit gamma-rays including relativistic compact stars, massive black holes in active galactic nuclei, gamma-ray burst sources, and our Sun during intense flares. Energetic cosmic rays can be accelerated and eventually smash gaseous environments in our Galaxy producinga strong diffuse gamma-ray emission. Gamma-rays reach the Earth also from remote regions of the Universe, providing crucial information on the cosmological evolution of energetic sources.

Many gamma-ray sources are transient, often on timescale of hours/days, showing a Universe in turmoil and subject to catastrophic events. Our understanding of many of these phenomena is preliminary, and a tremendous amount of observational and theoretical work is necessary to fully understand these energetic phenomena.

The mission AGILE (Astro-rivelatore Gamma a Immagini LEggero) will provide a powerful and cost-effective Observatory for gamma-ray (30 MeV-50 GeV) astrophysics during the years 2003-2005. No other gamma-ray mission sensitiveto photons above 30 MeV is being planned during the first five years of the next Millenium. AGILE is then planned to fill the gap between old and new generation gamma-ray missions with an innovative design and efficient scientific management. The mission ideally conforms to the faster, cheaper, better philosophy adopted by space agencies for scientific missions.

The AGILE scientific payload is based on the state-of-the-art and reliably developed technology of solid state silicon detectors. The instrument is very light (~80 kg) and effective in detecting and monitoring gamma-ray sources within a largefield of view ( ~1/5 of the whole sky). The baseline AGILE detector is sensitive in the energy range 30 MeV-50 GeV and it is characterized by the smallest everobtained deadtime for gamma-ray detection ( ~100 µs) and by a trigger based exclusively on silicon plane detectors. The instruments consists of a silicon-tungsten tracker, a cesium iodide mini-calorimeter, an anticoincidence system made of segmentedplastic scintillators, a X ray imaging detector based on an ultra light coded mask system, fast readout electronics and processing units.The baseline instrument is designed to achieve an optimal angular resolution (source location accuracy 5’-20’ for intense sources), an unprecedently large field-of-view ( >=2 sr), and a sensitivity comparable to that of EGRET for on axis (and substantially better for off-axis) point sources.

Despite its simplicity and moderate cost, AGILE is ideal to perform a large number of tasks: monitoring active galactic nuclei, detecting gamma-ray bursts with high efficiency, mapping the diffuse Galactic and extragalactic emission, studying pulsed gamma-ray emission from radiopulsars, monitoring the many unidentified sources and contributing to their unveiling, detecting energetic solarflares. Today, it is clear that successful investigations of gamma-ray sources rely on coordinated space and ground-based observations. The AGILE scientific program will be focussed on a prompt response to gamma-ray transients and alert for follow-up multiwavelength observations.AGILE will provide crucial information complementary to the many lower energydetectors that will be operational during the first decade of the new Millenium (INTEGRAL, XMM, AXAF, ASTRO-E, SPECTRUM-X, and others).

The AGILE mission is being planned as an Observatory with a scientific program of data analysis available to the Italian and international community on a competitive basis. Quicklook data analysis and fast communication of transientevents will be emphasized and implemented.

2. Physics achievements during 2000

AGILE has been approved for the phase C/D (which is the prototyping andconstruction phase) at the beginning of this year.

In the first part of the year, the architectural design of each subsystem has been completed.

As far as the subsystems under the responsabilities of the INFN groups are concerned, the tracker and the data acquisition systems, a detailed prototype work has been performed.

Three testbeams have been organized as milestones of this prototype development:

• May 2000 - CERN PS: the testbeam goal was the understanding of the behaviour of the silicon detector. The AGILE silicon tile is the biggest silicon detector which has been manufactured up to now. It has a dimension of 9.5x 9.5 cm²(6" wafer technology) with a readout strip pitch of 0.242 mm The readout is an analog one, which means that the information on the charge released by the particle is available. The trigger of the whole satellite is based on the silicon detectors.The results made it possible to start the final production. They have been presented at international conferences and are under publication.
• August 2000 - CERN PS: a feasibility study on the possibility of creating a tagged photon beam at the CERN PS has been performed. The final goal is the setup of a photon beam for the calibration of the whole payload and of future payloads for g rays (such as GLAST). The results are under publication.
• November 2000 - CERN PS: the testbeam goal will be the understanding of the AGILE trigger and data acquisition. Prototypes are being prepared for the Level 1 trigger and for the sparse readout (that is the readout of only the detectors that have given a trigger). The test will permit also to study the beahaviour of a mini-AGILE ensemble, made of 4 silicon tiles (representing4 planes), 8 CsI bars and the AC panels.

The final tracker front end ASIC has been designed and produced, in order to have a latch-up free ASIC. The laboratory setup for its test is being prepared. In the meanwhile, the main items of the mechanical structure are being studied, in order to choose materials and glues which can substain the temperature range and the vibrational stresses that the payload will undergo. This experience, in termsof results and industrial partners, is being used also by the GLAST collaboration.

3. INFN contribution to the experiment in terms of manpower and financial support

Three are the INFN groups involved in AGILE: Roma I, Roma II and Trieste, for a total of 7 FTE.

The Trieste group has the complete responsability of the AGILE heart, which is the silicon tracker, as far as the design, the prototypes and the final instrument are concerned.

The Roma II group is the coordinator of the data handling subsystem, which consists of the trigger system, the data acquisition, the power supply and the telemetry management.

The 3 groups are involved in the development of the simulation and analysis toolsand of the Level 2 software which has to be implemented on board.

The financial support from INFN for the year 2000 amounts to 416ML.

4. Number of publication in referred journals: 5

5. Number of talks to conferences: 6

6. Number of undergraduate and doctoral thesis on the experiment

3 Laurea Thesis in Physics completed

3 Laurea Thesis in Physics in progress

1 Diploma Thesis in Mechanical Engineering in progress

7. Leadership role in the experiment

In the present organization:

• Principal Investigator: Marco Tavani (IFCTR (CNR) Milano)
• Co-Principal Investigator of AGILE: Guido Barbiellini (INFN Trieste)
• Instrument scientist: Sandro Mereghetti (IFCTR (CNR) Milano)
• Instrument scientist: Aldo Morselli (INFN Roma II)
• Instrument Scientist and Program Manager of the AGILE tracker: Michela Prest (University of Trieste)

8. Innovative instruments

AGILE is the first example of a large quantity of silicon detectors (4 m² ) used on a satellite.

This requires the development of innovative technologies such as a compact space frame, a fast and low power electronics, a trigger processing able to reject a background which is 10⁴ higher than the expected signal.

Moreover, construction procedures adequate to the use of silicon detectors in a spatial environment (large temperature range, vibrational stresses up to 10 G) have to be developed.

The instrument is able to observe transient phenomena both in the X (10-40 keV) range and the gamma (30 MeV-50 GeV) one.

9. Competing experiments

As already said, during the operational period of AGILE, no other experiment able to study gamma rays above 30 MeV is foreseen.

In the year 2005, the launch of GLAST is scheduled. The technologies of the two satellites are very similar, but GLAST offers a much wider effective area and energy range.

10. International committee which has reviewed the experiment

The AGILE Phase B has been reviewed and approved for the phase C/D by an international committee appointed by ASI:

• Prof. Marcello Giorgi (University anf INFN of Pisa, Italy)
• Prof. Oscar Pace - ESA
• Prof. Jacques Paul (CE-Saclay, France)
• Dr. Luigi Piro (IAS-CNR Rome, Italy)
• Prof. Marco Salvati (Osservatorio Astrofisico di Arcetri, Italy)