MULTIWAVELENGTH OBSERVATIONS OF 3C 454.3. II. THEAGILE2007 DECEMBER CAMPAIGN

Abstract

We report on the second Astrorivelatore Gamma a Immagini Leggero (AGILE) multiwavelength campaign of the blazar 3C 454.3 during the first half of 2007 December. This campaign involved AGILE, Spitzer, Swift, Suzaku, the Whole Earth Blazar Telescope (WEBT) consortium, the Rapid Eye Mount (REM), and the Multicolor Imaging Telescopes for Survey and Monstrous Explosions (MITSuME) telescopes, offering a broadband coverage that allowed for a simultaneous sampling of the synchrotron and inverse Compton (IC) emissions. The two-week AGILE monitoring was accompanied by radio to optical monitoring by WEBT and REM, and by sparse observations in midinfrared and soft/hard X-ray energy bands performed by means of Target of Opportunity observations by Spitzer, Swift, and Suzaku, respectively. The source was detected with an average flux of ∼250 × 10 −8 photons cmabove 100 MeV, typical of its flaring states. The simultaneous optical and γ -ray monitoring allowed us to study the time lag associated with the variability in the two energy bands, resulting in a possible one-day delay of the γ -ray emission with respect to the optical one. From the simultaneous optical and γ -ray fast flare detected on December 12, we can constrain the delay between the γ -ray and optical emissions within 12 hr. Moreover, we obtain three spectral energy distributions (SEDs) with simultaneous data for 2007 December 5, 13, and 15, characterized by the widest multifrequency coverage. We found that a model with an external Compton on seed photons by a standard disk and reprocessed by the broad-line regions does not describe in a satisfactory way the SEDs of 2007 December 5, 13, and 15. An additional contribution, possibly from the hot corona with T = 10 6 K surrounding the jet, is required to account simultaneously for the softness of the synchrotron and the hardness of the IC emissions during those epochs.

The long-lasting activity of 3C 454.3

“…The data from AGILE and Fermi were separately used to study the correlations between flux variations in optical and γ-rays. All results agreed that the time lag of γ-ray flux variations after the optical 1 http://www.oato.inaf.it/blazars/webt/ 2 http://agile.iasf-roma.inaf.it/ 3 http://fermi.gsfc.nasa.gov/ ones is less than one day (Vercellone et al 2009;Donnarumma et al 2009;Bonning et al 2009;Vercellone et al 2010). Finke & Dermer (2010) discuss the spectral break at ∼2.4 GeV shown by Fermi data in August 2008 suggesting that it results from the combination of Compton-scattered disc and BLR radiations.…”

“…The results of these observations were published in Vercellone et al (2008), Raiteri et al (2008a,b), Vercellone et al (2009), Donnarumma et al (2009), Villata et al (2009a), and Vercellone et al (2010). Rotations of the optical polarisation vector both clockwise and counterclockwise were detected by Sasada et al (2010).…”

Multi-colour optical variability of the blazar 3C 454.3 in 2007–2010

“…For instance, an upper limit lag of about 1 day between IR/optical and gamma-ray fluxes has been reported (Bonning et al 2009;Vercellone et al 2010), while a possible delay between the gamma-ray and the optical is constrained to within 12 h (Donnarumma et al 2009;Vercellone et al 2009). …”

Multifrequency studies of the blazars detected by AGILE

“…3C 454.3 was the source best studied by AGILE because it is the blazar that dominates the γ-ray sky in the last years. A 18-month long monitoring from radio to γ-ray energy bands was available and the overall data were used in order to corroborate or falsify the evidence of 12-hour gamma-optical delay found during the December 2007 campaign (Donnarumma et al 2009a). The resulting DCF showed a peak at τ = 0, which implies no lag between optical and γ-ray emissions (see right panel in Fig.1).…”