This is the first report of Fermi Gamma-Ray Space Telescope observations of the quasar 3C 454.3, which has been undergoing pronounced long-term outbursts since 2000. The data from the Large Area Telescope, covering 2008 July 7-October 6, indicate strong, highly variable γ-ray emission with an average flux of ~3 × 10–6 photons cm–2 s–1, for energies >100 MeV. The γ-ray flux is variable, with strong, distinct, symmetrically shaped flares for which the flux increases by a factor of several on a timescale of about 3 days. This variability indicates a compact emission region, and the requirement that the source is optically thin to pair production implies relativistic beaming with Doppler factor δ>8, consistent with the values inferred from Very Long Baseline Interferometry observations of superluminal expansion (δ ~ 25). The observed γ-ray spectrum is not consistent with a simple power law, but instead steepens strongly above ~2 GeV, and is well described by a broken power law with photon indices of ~2.3 and ~3.5 below and above the break, respectively. This is the first direct observation of a break in the spectrum of a high-luminosity blazar above 100 MeV, and it is likely direct evidence for an intrinsic break in the energy distribution of the radiating particles. Alternatively, the spectral softening above 2 GeV could be due to γ-ray absorption via photon-photon pair production on the soft X-ray photon field of the host active galactic nucleus, but such an interpretation would require the dissipation region to be located very close (lsim100 gravitational radii) to the black hole, which would be inconsistent with the X-ray spectrum of the source.
|Autori:||Abdo AA; Ackermann M; Ajello M; Atwood WB; Axelsson M; Baldini L; Ballet J; Barbiellini G; Bastieri D; Battelino M; Baughman BM; Bechtol K; Bellazzini R; Berenji B; Blandford RD; Bloom ED; Bonamente E; Borgland AW; Bouvier A; Bregeon J; Brez A; Brigida M; Bruel P; Burnett TH; Caliandro GA; Cameron RA; Caraveo PA; Casandjian JM; Cavazzuti E; Cecchi C; Charles E; Chaty S; Chekhtman A; Cheung CC; Chiang J; Ciprini S; Claus R; Cohen-Tanugi J; Cominsky LR; Conrad J; Costamante L; Cutini S; Dermer CD; de Angelis A; de Palma F; Digel SW; Silva EDE; Donato D; Drell PS; Dubois R; Dumora D; Farnier C; Favuzzi C; Focke WB; Foschini L; Frailis M; Fuhrmann L; Fukazawa Y; Funk S; Fusco P; Gargano F; Gasparrini D; Gehrels N; Germani S; Giebels B; Giglietto N; Giommi P; Giordano F; Glanzman T; Godfrey G; Grenier IA; Grondin MH; Grove JE; Guillemot L; Guiriec S; Hanabata Y; Harding AK; Hartman RC; Hayashida M; Hays E; Hughes RE; Johannesson G; Johnson AS; Johnson RP; Johnson WN; Kamae T; Katagiri H; Kataoka J; Kawai N; Kerr M; Knodlseder J; Kocian ML; Kuehn F; Kuss M; Latronico L; Lee SH; Lemoine-Goumard M; Longo F; Loparco F; Lott B; Lovellette MN; Lubrano P; Madejski GM; Makeev A; Massaro E; Mazziotta MN; McEnery JE; McGlynn S; Meurer C; Michelson PF; Mitthumsiri W; Mizuno T; Moiseev AA; Monte C; Monzani ME; Morselli A; Moskalenko IV; Murgia S; Nolan PL; Norris JP; Nuss E; Ohsugi T; Omodei N; Orlando E; Ormes JF; Paneque D; Panetta JH; Parent D; Pelassa V; Pepe M; Pesce-Rollins M; Piron F; Porter TA; Raino S; Rando R; Razzano M; Reimer A; Reimer O; Reposeur T; Reyes LC; Ritz S; Rochester LS; Rodriguez AY; Rahoui F; Ryde F; Sadrozinski HFW; Sambruna R; Sanchez D; Sander A; Parkinson PMS; Sgro C; Shaw MS; Smith DA; Smith PD; Spandre G; Spinelli P; Starck JL; Strickman MS; Suson DJ; Tajima H; Takahashi H; Takahashi T; Tanaka T; Thayer JB; Thayer JG; Thompson DJ; Tibaldo L; Torres DF; Tosti G; Tramacere A; Uchiyama Y; Usher TL; Vilchez N; Villata M; Vitale V; Waite AP; Winer BL; Wood KS; Ylinen T; Zensus JA; Ziegler M|
|Titolo:||EARLY FERMI GAMMA-RAY SPACE TELESCOPE OBSERVATIONS OF THE QUASAR 3C 454.3|
|Anno del prodotto:||2009|
|Digital Object Identifier (DOI):||10.1088/0004-637X/699/1/817|
|Appare nelle tipologie:||1.1 Articolo in rivista|