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Ten years of AGILE: the mission and scientific highlights

  • A Decade of AGILE
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Rendiconti Lincei. Scienze Fisiche e Naturali Aims and scope Submit manuscript

Abstract

We review the main features and scientific results obtained during the first 10 years of the AGILE space Mission, a scientific program of the Italian Space Agency (ASI) focused on high-energy astrophysics. The Mission was proposed in 1997 for the ASI “Small Mission” Program and the instrument has been developed with the programmatic and technical support of INAF and INFN. The AGILE satellite was launched on April 23, 2007, from the Indian base in Sriharikota. We describe first the characteristics of the instrument and of the satellite. AGILE is a very innovative space Mission for its class, and is capable of reaching an optimal scientific performance for the study of astrophysical sources with detectors operating in the energy ranges 20–60 keV, 400 keV–100 MeV, 50 MeV–30 GeV. We review the main scientific achievements of the Mission with contributions to the study of the most energetic Galactic and extragalactic sources including accreting compact objects (neutron stars and black holes), pulsars, Supernova Remnants, Active Galactic Nuclei (AGN). AGILE made several important discoveries: a novel mechanism of particle acceleration operating in the Crab Nebula, the emission of transient gamma rays at the moment of launching of relativistic jets from Galactic compact sources, the first evidence of hadronic cosmic ray production from Galactic sources, the emission of very powerful gamma-ray flares from accreting super-massive black holes in AGN, sudden spectral transitions in gamma-ray bursts. Furthermore, AGILE is now providing unique contributions for the study of gravitational wave source counterparts and cosmic neutrino emitters. Also terrestrial applications are relevant for the science program: AGILE discovered gamma-ray emission above 20 MeV from Terrestrial gamma-ray flashes produced by powerful lighting and thunderstorms. This discovery has an important impact for environmental and atmospheric studies. In addition, particle resonance effects and time-dependent precipitations in the lower Earth magnetosphere can by addressed by AGILE studying the charged particles detected by the instrument. The AGILE satellite is operating nominally, and continues to observe the sky searching for the most energetic phenomena of our Universe.

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Notes

  1. Details about the AGILE scientific program can be found in http://www.ssdc.asi.it.

  2. Recognizing the importance of this event was facilitated by a previous “anomalous” detection by AGILE of the Crab with similar characteristics. Indeed, in October 2007 (i.e., at the beginning of the satellite scientific operations) AGILE detected an early episode of gamma-ray flaring from the Crab (see also Pittori 2009). This episode lasted \(\sim \) 2 weeks, and showed an interesting time sub-structure. The peak flux was reached on Oct. 7, 2007, and the 1-day integration value was \(F_{\gamma ,p2} =(8.9 \pm 1.1) \times 10^{-6} \text { ph cm}^{-2} \, \text {s}^{-1}\) (\(\alpha '' = 2.05 \,\pm \, 0.13)\). However, this isolated puzzling episode needed further investigation in 2007, and especially it required a full confirmation before acquiring full confidence of the Crab variability at gamma-ray energies.

  3. In order to model the observed flare spectra, we assume that a sub-class of the overall particle population in the inner Nebula is subject to an impulsive acceleration process at a specific site. In principle, favorably Doppler-boosted synchrotron emission of quasi mono-energetic particles with \(\delta \sim \) 5–10 might explain the gamma-ray spectra of Figs. 13 and 14. However, it is not clear whether this large Doppler boosting is supported by the overall Crab Nebula data and geometry (for a discussion, see ref. Komissarov and Lyutikov 2011). Alternately, a particle acceleration mechanism with an “effective” \(E/B \ge 1\) and \(\delta \sim 1\) seems to be required.

  4. See also refs. (Buehler and Blandford 2014; Blandford and Buehler 2017) for a particular view on the subject.

  5. The predicted neutrino emission from Cyg X-3 is currently too low to be detected by ICECUBE-like detectors (Sahakyan et al. 2014). However, new generation neutrino instruments might address this important issue in the future.

  6. We need, therefore, a new sensitive instrument in the range MeV–GeV to study this and other powerful Galactic micro-quasars. See the considerations about the new project ASTROGAM at the end of this paper.

  7. A null detection in the GeV range was also obtained by Fermi-LAT in its early operational phases. The puzzle was resolved years later, with the Fermi-LAT detection of a quite steep spectrum peaking at 100 GeV energies (Abdo 2011b); this spectrum is consistent with electron IC emission.

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Acknowledgements

The AGILE program has been developed over the years under the auspices of the Italian Space Agency with co-participation of the Italian Institute of Astrophysics (INAF) and of the Italian Institute of Nuclear Physics (INFN). Important support in the early phases of the project has been provided by CNR and ENEA. The scientific research carried out for the project has been partially supported under the grants ASI-I/R/045/04 and ASI-I/089/06/0,1,2 and subsequent grants. We acknowledge the crucial programmatic support of many colleagues in charge of Italian scientific institutions during two decades 1997–2017: the former ASI Scientific Director and ASI President G.F. Bignami, the former CNR President L. Bianco, the ASI Presidents S. De Julio, S. Vetrella, G. Bignami, E. Saggese, R. Battiston; the INAF Presidents P. Benvenuti, T. Maccacaro, G.F. Bignami, and N. D’Amico, and the INFN Presidents L. Maiani, R. Petronzio, F. Ferroni. We recognize the inspiration and enthusiasm of the late Giovanni (Nanni) Bignami who strongly supported the AGILE program over the years since its inception. Nanni is not with us anymore, but we hope that the AGILE work continues the tradition of Italian high-energy astrophysics at the highest level as he always wanted to pursue. A large number of scientists and engineers contributed to the success of the Mission in a substantial way at different stages of the project. We mention here the coordinators of the ASI Scientific Directorate S. Di Pippo and B. Negri, the AGILE Mission Directors of ASI L. Salotti, G. Valentini, F. D’Amico, the AGILE Team Program Manager A. Zambra, and the industry executive Directors L. Zucconi, M. Muscinelli, A. Beretta, R. Aceti, F. Longoni, R. Cordoni, R. Starec, and the managers G. Cafagna, B.L. Maltecca, and R. Terpin. A special recognition is for the AGILE CGS Program Manager, the late Paolo Sabatini, who contributed in a fundamental way to the success of the AGILE satellite development and early operations. We acknowledge the outstanding technical and management performance of the ISRO personnel during the AGILE launch campaign in India. Special thanks go to the ISRO Sriharikota base Director A. Nair and to the PSLV C-8 launch Director N. Narayanamoorthy and his very skilled team. Crucial support to the Mission has been provided by the AGILE Team Scientific Secretariat members who greatly contributed over the years: C. Mangili, B. Schena, E. Scalise, L. Siciliano, M. Giusti. A special recognition is for the unfailing support given to AGILE by the CIFS Director A. Ferrari and by the CIFS Scientific Secretariat (G. Ardizzoia). Updated documentation on the AGILE Mission can be found at the web sites http://www.ssdc.asi.it, and http://agile.iaps.inaf.it. The APP “AGILEScience” is publicly available for smartphones.

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  1. INAF/IAPS, Roma via del Fosso del Cavaliere 100, 00133, Rome, Italy

    Marco Tavani

  2. Dipartimento di Fisica, Universitá di Roma Tor Vergata, Rome, Italy

    Marco Tavani

  3. Accademia Nazionale dei Lincei, via della Lungara 10, 00165, Rome, Italy

    Marco Tavani

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Tavani, M. Ten years of AGILE: the mission and scientific highlights. Rend. Fis. Acc. Lincei 30 (Suppl 1), 13–50 (2019). https://doi.org/10.1007/s12210-019-00841-5

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