Fermi Large Area Telescope Detection of Extended Gamma-Ray Emission from the Radio Galaxy Fornax A
Journal
Date Issued
2016
Author(s)
Ackermann, M.
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Ajello, M.
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Baldini, L.
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Ballet, J.
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Barbiellini, G.
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Bastieri, D.
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Bellazzini, R.
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Bissaldi, E.
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Blandford, R. D.
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Bloom, E. D.
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Bonino, R.
•
Fermi LAT Collaboration
•
Bruel, P.
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Buehler, R.
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Buson, S.
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Caliandro, G. A.
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Cameron, R. A.
•
Caragiulo, M.
•
•
Cavazzuti, E.
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Cecchi, C.
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de Palma, F.
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Charles, E.
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Chekhtman, A.
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Cheung, C. C.
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Chiaro, G.
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Ciprini, S.
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Cohen, J. M.
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Cohen-Tanugi, J.
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Costanza, F.
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Cutini, S.
•
•
Desiante, R.
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Davis, D. S.
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de Angelis, A.
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Digel, S. W.
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Di Lalla, N.
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Di Mauro, M.
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Di Venere, L.
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Favuzzi, C.
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Fegan, S. J.
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Ferrara, E. C.
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Focke, W. B.
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Guiriec, S.
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Fukazawa, Y.
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Funk, S.
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Fusco, P.
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Gargano, F.
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Gasparrini, D.
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Georganopoulos, M.
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Giglietto, N.
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Giordano, F.
•
•
Godfrey, G.
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Hays, E.
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Green, D.
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Grenier, I. A.
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Hewitt, J. W.
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Hill, A. B.
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Jogler, T.
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Jóhannesson, G.
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Kensei, S.
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Kuss, M.
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Larsson, S.
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Latronico, L.
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Michelson, P. F.
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Li, J.
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Li, L.
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Longo, F.
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Loparco, F.
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Lubrano, P.
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Magill, J. D.
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Maldera, S.
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Manfreda, A.
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Mayer, M.
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Mazziotta, M. N.
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Mitthumsiri, W.
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McConville, W.
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McEnery, J. E.
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Mizuno, T.
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Monzani, M. E.
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Morselli, A.
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Moskalenko, I. V.
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Murgia, S.
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Negro, M.
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Nuss, E.
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Ohno, M.
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Razzano, M.
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Ohsugi, T.
•
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Orlando, E.
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Ormes, J. F.
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Paneque, D.
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Perkins, J. S.
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Pesce-Rollins, M.
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Piron, F.
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Pivato, G.
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Porter, T. A.
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Reimer, A.
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Rainò, S.
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Rando, R.
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Reimer, O.
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Schmid, J.
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Sgrò, C.
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Simone, D.
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Siskind, E. J.
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Spada, F.
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Spandre, G.
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Spinelli, P.
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Brandt, T. J.
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Stawarz, Ł.
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Takahashi, H.
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Thayer, J. B.
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Thompson, D. J.
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Torres, D. F.
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Tosti, G.
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Troja, E.
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Vianello, G.
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Wood, K. S.
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Wood, M.
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Bregeon, J.
•
Zimmer, S.
Abstract
We report the Fermi Large Area Telescope detection of extended γ-ray emission from the lobes of the radio galaxy Fornax A using 6.1 years of Pass 8 data. After Centaurus A, this is now the second example of an extended γ-ray source attributed to a radio galaxy. Both an extended flat disk morphology and a morphology following the extended radio lobes were preferred over a point-source description, and the core contribution was constrained to be < 14% of the total γ-ray flux. A preferred alignment of the γ-ray elongation with the radio lobes was demonstrated by rotating the radio lobes template. We found no significant evidence for variability on ∼0.5 year timescales. Taken together, these results strongly suggest a lobe origin for the γ-rays. With the extended nature of the > 100 MeV γ-ray emission established, we model the source broadband emission considering currently available total lobe radio and millimeter flux measurements, as well as X-ray detections attributed to inverse Compton (IC) emission off the cosmic microwave background (CMB). Unlike the Centaurus A case, we find that a leptonic model involving IC scattering of CMB and extragalactic background light (EBL) photons underpredicts the γ-ray fluxes by factors of about ∼2-3, depending on the EBL model adopted. An additional γ-ray spectral component is thus required, and could be due to hadronic emission arising from proton-proton collisions of cosmic rays with thermal plasma within the radio lobes.
Volume
826
Issue
1
Start page
1
Issn Identifier
0004-637X
Ads BibCode
2016ApJ...826....1A
Rights
open.access
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