AGILE observation of a gamma-ray flare from the blazar 3C 279

¹ INAF/IASF–Milano, via E. Bassini 15, 20133 Milano, Italy e-mail: giuliani@iasf-milano.inaf.it
² INAF/IASF–Roma, via Fosso del Cavaliere 100, 00133 Roma, Italy
³ Dip. di Fisica, Univ. “Tor Vergata”, via della Ricerca Scientifica 1, 00133 Roma, Italy
⁴ CIFS–Torino, Viale Settimio Severo 3, 10133 Torino, Italy
⁵ INAF/IASF–Bologna, via Gobetti 101, 40129 Bologna, Italy
⁶ Dip. di Fisica and INFN, via Valerio 2, 34127 Trieste, Italy
⁷ Dip. di Fisica, Univ. di Perugia, via Pascoli, 06123 Perugia, Italy
⁸ INFN–Pavia, via Bassi 6, 27100 Pavia, Italy
⁹ Dip. Fisica Nucleare e Teorica, Univ. di Pavia, via Bassi 6, 27100 Pavia, Italy
¹⁰ ENEA–Bologna, via dei Martiri di Monte Sole 4, 40129 Bologna, Italy
¹¹ INFN–Roma “La Sapienza”, Piazzale A. Moro 2, 00185 Roma, Italy
¹² INFN–Roma “Tor Vergata”, via della Ricerca Scientifica 1, 00133 Roma, Italy
¹³ Dip. di Fisica, Univ. dell'Insubria, via Valleggio 11, 22100 Como, Italy
¹⁴ ENEA–Roma, via E. Fermi 45, 00044 Frascati (Roma), Italy
¹⁵ ASI–ASDC, via G. Galilei, 00044 Frascati (Roma), Italy
¹⁶ ASI, Viale Liegi 26, 00198 Roma, Italy

Received: 11 August 2008
Accepted: 10 October 2008

Abstract

Context. We report the detection by the AGILE satellite of an intense gamma-ray flare from the gamma-ray source 3EG J1255-0549, associated with the Flat Spectrum Radio Quasar 3C 279, during the AGILE pointings towards the Virgo Region on 2007 July 9-13.

Aims. The simultaneous optical, X-ray and gamma-ray covering allows us to study the spectral energy distribution (SED) and the theoretical models relative to the mid-July flaring episode.

Methods. AGILE observed the source during its Science Performance Verification Phase with its two co-aligned imagers: the Gamma-Ray Imaging Detector (GRID) and the hard X-ray imager (Super-AGILE) sensitive in the 30 MeV-50 GeV and 18-60 keV respectively. During the AGILE observation the source was monitored simultaneously in the optical band by the REM telescope and in the X-ray band by the Swift satellite through 4 target of opportunity observations.

Results. During 2007 July 9-13, AGILE-GRID detected gamma-ray emission from 3C 279, with the source at ~2° from the center of the field of view, with an average flux of (210 ± 38)  10^-8 ph cm^-2 s^-1 for energy above 100 MeV. No emission was detected by Super-AGILE, with a 3-σ upper limit of 10 mCrab. During the observation, which lasted about 4 days, no significative gamma-ray flux variation was observed.

Conclusions. The Spectral Energy Distribution is modelled with a homogeneous one-zone Synchrotron Self Compton emission plus the contributions by external Compton scattering of the direct disk radiation and, to a lesser extent, by external Compton scattering of photons from the Broad Line Region.