Calibration of AGILE-GRID with in-flight data and Monte Carlo simulations

¹ INAF/IASF-Milano, via E. Bassini 15, 20133 Milano, Italy
e-mail: chen@iasf-milano.inaf.it
² INAF/IAPS, via Fosso del Cavaliere 100, 00133 Roma, Italy
³ INAF/IASF-Bologna, via Gobetti 101, 40129 Bologna, Italy
⁴ INFN-Pavia, via Agostino Bassi 6, 27100 Pavia, Italy
⁵ ASI Science Data Center, via Galileo Galilei, 00044 Frascati Roma, Italy
⁶ INAF OAR, via di Frascati 33, 00040 Monteporzio Catone, Roma, Italy
⁷ ENEA Frascati, via Enrico Fermi 13, 00044 Frascati (Roma), Italy
⁸ Dip. di Fisica, Univ. Tor Vergata, via della Ricerca Scientifica 1, 00133 Roma, Italy
⁹ CIFS, Villa Gualino – v.le Settimio Severo 63, 10133 Torino, Italy
¹⁰ INAF-OAC, localita’ Poggio dei Pini, strada 54, 09012 Capoterra (CA), Italy
¹¹ Dip. Fisica, Univ. Trieste and INFN Trieste, via A. Valerio 2, 34127 Trieste, Italy
¹² School of Physics, University of the Witwatersrand, Johannesburg Wits 2050, South Africa
¹³ Dip. Fisica, Universitá di Torino, via Giuria 1, 10125 Torino, Italy
¹⁴ ENEA – Bologna, via Martiri Montesole 4, 40129 Bologna, Italy
¹⁵ INFN – Roma La Sapienza, P.le A. Moro 2, 00185 Roma, Italy
¹⁶ INFN Roma Tor Vergata, via della Ricerca Scientifica 1, 00133 Roma, Italy
¹⁷ Dip. di Fisica, Univ. Dell’Insubria, via Valleggio 11, 22100 Como, Italy
¹⁸ Agenzia Spaziale Italiana, Viale Liegi 26, 00198 Roma, Italy
¹⁹ INAF – IASF Palermo, via Ugo La Malfa 153, 90146 Palermo, Italy
²⁰ ASTRON, the Netherlands Institute for Radio Astronomy, Postbus 2, 7990 AA, Dwingeloo, The Netherlands
²¹ Royal Institute of Technology (KTH), Stockholm, Sweden
²² The Oskar Klein Centre for Cosmoparticle Physics, Stockholm, Sweden

Received: 24 April 2013
Accepted: 27 August 2013

Abstract

Context. AGILE is a γ-ray astrophysics mission which has been in orbit since 23 April 2007 and continues to operate reliably. The γ-ray detector, AGILE-GRID, has observed Galactic and extragalactic sources, many of which were collected in the first AGILE Catalog.

Aims. We present the calibration of the AGILE-GRID using in-flight data and Monte Carlo simulations, producing instrument response functions (IRFs) for the effective area (A_eff), energy dispersion probability (EDP), and point spread function (PSF), each as a function of incident direction in instrument coordinates and energy.

Methods. We performed Monte Carlo simulations at different γ-ray energies and incident angles, including background rejection filters and Kalman filter-based γ-ray reconstruction. Long integrations of in-flight observations of the Vela, Crab and Geminga sources in broad and narrow energy bands were used to validate and improve the accuracy of the instrument response functions.

Results. The weighted average PSFs as a function of spectra correspond well to the data for all sources and energy bands.

Conclusions. Changes in the interpolation of the PSF from Monte Carlo data and in the procedure for construction of the energy-weighted effective areas have improved the correspondence between predicted and observed fluxes and spectra of celestial calibration sources, reducing false positives and obviating the need for post-hoc energy-dependent scaling factors. The new IRFs have been publicly available from the AGILE Science Data Center since November 25, 2011, while the changes in the analysis software will be distributed in an upcoming release.