Multiwavelength Observations of 3c 454.3. I. The Agile 2007 November Campaign on the ''crazy Diamond''
Articolo
Data di Pubblicazione:
2009
Abstract:
We report on amultiwavelength observation of the blazar 3C 454.3 (which we dubbed crazy diamond) carried out on
November 2007 by means of the astrophysical satellites AGILE, International Gamma-Ray Astrophysics Laboratory
(INTEGRAL), Swift, the Whole Earth Blazar Telescope (WEBT) Consortium, and the optical–NIR telescope Rapid
EyeMount (REM). Thanks to thewide field of viewof the AGILE satellite and its prompt alert dissemination to other
observatories, we obtained a long (three weeks), almost continuous γ -ray coverage of the blazar 3C 454.3 across 14
decades of energy. This broadband monitoring allows us to study in great detail light curves, correlations, time lags,
and spectral energy distributions (SEDs) during different physical states. Gamma-ray data were collected during an
AGILE pointing toward the Cygnus Region. Target of Opportunity (ToO) observations were performed to follow up
the γ -ray observations in the soft and hard X-ray energy bands. Optical data were acquired continuously by means
of a preplanned WEBT campaign and through an REM ToO repointing. 3C 454.3 is detected at a ∼19σ level during
the three-week observing period, with an average flux above 100 MeV of FE>100MeV = (170±13)×10−8 photons
cm−2 s−1. The γ -ray spectrum can be fitted with a single power law with photon index ΓGRID = 1.73 ± 0.16
between 100 MeV and 1 GeV. We detect significant day-by-day variability of the γ -ray emission during our
observations, and we can exclude that the fluxes are constant at the 99.6% (∼ 2.9σ) level. The source was detected
typically around 40 deg off-axis, and it was substantially off–axis in the field of view of the AGILE hard X-ray
imager. However, a five-day long ToO observation by INTEGRAL detected 3C 454.3 at an average flux of about
F20–200 keV = 1.49 × 10−3 photons cm−2 s−1with an average photon index of ΓIBIS = 1.75 ± 0.24 between 20–
200 keV. Swift also detected 3C 454.3 with a flux in the 0.3–10 keV energy band in the range (1.23–1.40) × 10−2
photons cm−2 s−1 and a photon index in the range ΓXRT = 1.56–1.73. In the optical band, both WEBT and
REM show an extremely variable behavior in the R band. A correlation analysis based on the entire data set is
consistent with no time lags between the γ -ray and the optical flux variations. Our simultaneous multifrequency
observations strongly indicate that the dominant emission mechanism between 30 MeV and 30 GeV is dominated
by inverse Compton scattering of relativistic electrons in the jet on the external photons from the broad line region.
Tipologia CRIS:
03A-Articolo su Rivista
Keywords:
galaxies: active – galaxies: jets – quasars: general – quasars: individual (3C 454.3) – radiation
mechanisms: non-thermal
Elenco autori:
S. Vercellone; A. W. Chen; V. Vittorini; A. Giuliani; F. D'Ammando; M. Tavani; I. Donnarumma; G. Pucella; C. M. Raiteri; M. Villata; W. P. Chen; G. Tosti; D. Impiombato; P. Romano; A. Belfiore; A. DeLuca; G. Novara; F. Senziani; A. Bazzano; M. T. Fiocchi; P. Ubertini; A. Ferrari; A. Argan; G. Barbiellini; F. Boffelli; A. Bulgarelli; P. Caraveo; P. W. Cattaneo; V. Cocco; E. Costa; E. DelMonte; G. DeParis; G. Di Cocco; Y. Evangelista; M. Feroci; M. Fiorini; F. Fornari; T. Froysland; F. Fuschino; M. Galli; F. Gianotti; C. Labanti; I. Lapshov; F. Lazzarotto; P. Lipari; F. Longo; M. Marisaldi; S. Mereghetti; A. Morselli; A. Pellizzoni; L. Pacciani; F. Perotti; P. Picozza; M. Prest; M. Rapisarda; A. Rappoldi; P. Soffitta; M. Trifoglio; A. Trois; E. Vallazza; A. Zambra; D. Zanello; C. Pittori; F. Verrecchia; P. Santolamazza; B. Preger; D. Gasparrini; S. Cutini; P. Giommi; S. Colafrancesco; L. Salotti
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