The starburst galaxy NGC 253 revisited by H.E.S.S. and Fermi-LAT
Journal
Date Issued
2018
Author(s)
H. E. S. S. Collaboration
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Abdalla, H.
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Aharonian, F.
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Ait Benkhali, F.
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Angüner, E. O.
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Arakawa, M.
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Arcaro, C.
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Armand, C.
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Arrieta, M.
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Backes, M.
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Barnard, M.
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Becherini, Y.
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Becker Tjus, J.
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Berge, D.
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Bernhard, S.
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Bernlöhr, K.
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Blackwell, R.
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Böttcher, M.
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Boisson, C.
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Bolmont, J.
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Bonnefoy, S.
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Bordas, P.
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Bregeon, J.
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Brun, F.
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Brun, P.
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Bryan, M.
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Büchele, M.
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Bulik, T.
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Bylund, T.
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Capasso, M.
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Caroff, S.
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Casanova, S.
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Cerruti, M.
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Chakraborty, N.
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Chandra, S.
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Chaves, R. C. G.
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Chen, A.
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Colafrancesco, S.
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Condon, B.
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Davids, I. D.
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Deil, C.
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Devin, J.
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deWilt, P.
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Dirson, L.
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Djannati-Ataï, A.
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Dmytriiev, A.
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Donath, A.
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Drury, L. O. 'C.
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Dyks, J.
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Egberts, K.
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Emery, G.
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Ernenwein, J. -P.
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Eschbach, S.
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Fegan, S.
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Fiasson, A.
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Fontaine, G.
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Funk, S.
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Füßling, M.
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Gabici, S.
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Gallant, Y. A.
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Garrigoux, T.
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Gaté, F.
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Giavitto, G.
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Glawion, D.
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Glicenstein, J. F.
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Gottschall, D.
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Grondin, M. -H.
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Hahn, J.
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Haupt, M.
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Heinzelmann, G.
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Henri, G.
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Hermann, G.
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Hinton, J. A.
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Hofmann, W.
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Hoischen, C.
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Holch, T. L.
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Holler, M.
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Horns, D.
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Huber, D.
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Iwasaki, H.
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Jacholkowska, A.
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Jamrozy, M.
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Jankowsky, D.
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Jankowsky, F.
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Jouvin, L.
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Jung-Richardt, I.
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Kastendieck, M. A.
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Kataŕnski, K.
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Katsuragawa, M.
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Katz, U.
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Kerszberg, D.
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Khangulyan, D.
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Khélifi, B.
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King, J.
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Klepser, S.
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Ḱzniak, W.
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Komin, Nu.
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Kosack, K.
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Krakau, S.
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Kraus, M.
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Krüger, P. P.
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Lamanna, G.
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Lau, J.
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Lefaucheur, J.
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Lemière, A.
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Lemoine-Goumard, M.
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Lenain, J. -P.
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Leser, E.
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Lohse, T.
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Lorentz, M.
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López-Coto, R.
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Lypova, I.
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Malyshev, D.
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Marandon, V.
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Marcowith, A.
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Mariaud, C.
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Martí-Devesa, G.
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Marx, R.
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Maurin, G.
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Meintjes, P. J.
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Mitchell, A. M. W.
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Moderski, R.
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Mohamed, M.
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Mohrmann, L.
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Moulin, E.
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Murach, T.
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Nakashima, S.
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de Naurois, M.
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Ndiyavala, H.
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Niederwanger, F.
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Niemiec, J.
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Oakes, L.
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O'Brien, P.
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Odaka, H.
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Ohm, S.
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Ostrowski, M.
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Oya, I.
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Panter, M.
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Parsons, R. D.
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Perennes, C.
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Petrucci, P. -O.
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Peyaud, B.
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Piel, Q.
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Pita, S.
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Poireau, V.
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Priyana Noel, A.
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Prokhorov, D. A.
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Prokoph, H.
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Pühlhofer, G.
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Punch, M.
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Quirrenbach, A.
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Raab, S.
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Rauth, R.
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Reimer, A.
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Reimer, O.
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Renaud, M.
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Rieger, F.
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Rinchiuso, L.
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Romoli, C.
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Rowell, G.
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Rudak, B.
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Ruiz-Velasco, E.
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Sahakian, V.
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Saito, S.
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Sanchez, D. A.
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Santangelo, A.
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Sasaki, M.
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Schlickeiser, R.
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Schüssler, F.
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Schulz, A.
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Schwanke, U.
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Schwemmer, S.
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Seglar-Arroyo, M.
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Senniappan, M.
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Seyffert, A. S.
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Shafi, N.
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Shilon, I.
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Shiningayamwe, K.
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Simoni, R.
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Sinha, A.
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Sol, H.
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Spanier, F.
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Specovius, A.
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Spir-Jacob, M.
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Stawarz, Ł.
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Steenkamp, R.
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Stegmann, C.
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Steppa, C.
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Sushch, I.
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Takahashi, T.
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Tavernet, J. -P.
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Tavernier, T.
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Taylor, A. M.
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Terrier, R.
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Tibaldo, L.
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Tiziani, D.
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Tluczykont, M.
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Trichard, C.
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Tsirou, M.
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Tsuji, N.
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Tuffs, R.
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Uchiyama, Y.
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van der Walt, D. J.
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van Eldik, C.
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van Rensburg, C.
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van Soelen, B.
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Vasileiadis, G.
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Veh, J.
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Venter, C.
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Viana, A.
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Vincent, P.
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Vink, J.
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Voisin, F.
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Völk, H. J.
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Vuillaume, T.
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Wadiasingh, Z.
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Wagner, S. J.
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Wagner, P.
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Wagner, R. M.
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White, R.
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Wierzcholska, A.
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Wörnlein, A.
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Yang, R.
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Zaborov, D.
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Zacharias, M.
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Zanin, R.
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Zdziarski, A. A.
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Zech, A.
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Zefi, F.
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Ziegler, A.
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Zorn, J.
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Żywucka, N.
Abstract
Context. NGC 253 is one of only two starburst galaxies found to emit γ-rays from hundreds of MeV to multi-TeV energies. Accurate measurements of the very-high-energy (VHE; E > 100 GeV) and high-energy (HE; E > 60 MeV) spectra are crucial to study the underlying particle accelerators, probe the dominant emission mechanism(s) and to study cosmic-ray interaction and transport.
Aims: The measurement of the VHE γ-ray emission of NGC 253 published in 2012 by H.E.S.S. was limited by large systematic uncertainties. Here, the most up to date measurement of the γ-ray spectrum of NGC 253 is investigated in both HE and VHE γ-rays. Assuming a hadronic origin of the γ-ray emission, the measurement uncertainties are propagated into the interpretation of the accelerated particle population.
Methods: The data of H.E.S.S. observations are reanalysed using an updated calibration and analysis chain. The improved Fermi-LAT analysis employs more than 8 yr of data processed using pass 8. The cosmic-ray particle population is evaluated from the combined HE-VHE γ-ray spectrum using NAIMA in the optically thin case.
Results: The VHE γ-ray energy spectrum is best fit by a power-law distribution with a flux normalisation of (1.34 ± 0.14stat ± 0.27sys) × 10-13 cm-2 s-1 TeV1 at 1 TeV - about 40% above, but compatible with the value obtained in Abramowski et al. (2012). The spectral index Γ = 2.39 ± 0.14stat ± 0.25sys is slightly softer than but consistent with the previous measurement within systematic errors. In the Fermi energy range an integral flux of F(E > 60 MeV) = (1.56 ± 0.28stat ± 0.15sys) × 10-8 cm-2 s-1 is obtained. At energies above ∼3 GeV the HE spectrum is consistent with a power-law ranging into the VHE part of the spectrum measured by H.E.S.S. with an overall spectral index Γ = 2.22 ± 0.06stat.
Conclusions: Two scenarios for the starburst nucleus are tested, in which the gas in the starburst nucleus acts as either a thin or a thick target for hadronic cosmic rays accelerated by the individual sources in the nucleus. In these two models, the level to which NGC 253 acts as a calorimeter is estimated to a range of fcal = 0.1 to 1 while accounting for the measurement uncertainties. The presented spectrum is likely to remain the most accurate measurements until the Cherenkov Telescope Array (CTA) has collected a substantial set of data towards NGC 253.
Aims: The measurement of the VHE γ-ray emission of NGC 253 published in 2012 by H.E.S.S. was limited by large systematic uncertainties. Here, the most up to date measurement of the γ-ray spectrum of NGC 253 is investigated in both HE and VHE γ-rays. Assuming a hadronic origin of the γ-ray emission, the measurement uncertainties are propagated into the interpretation of the accelerated particle population.
Methods: The data of H.E.S.S. observations are reanalysed using an updated calibration and analysis chain. The improved Fermi-LAT analysis employs more than 8 yr of data processed using pass 8. The cosmic-ray particle population is evaluated from the combined HE-VHE γ-ray spectrum using NAIMA in the optically thin case.
Results: The VHE γ-ray energy spectrum is best fit by a power-law distribution with a flux normalisation of (1.34 ± 0.14stat ± 0.27sys) × 10-13 cm-2 s-1 TeV1 at 1 TeV - about 40% above, but compatible with the value obtained in Abramowski et al. (2012). The spectral index Γ = 2.39 ± 0.14stat ± 0.25sys is slightly softer than but consistent with the previous measurement within systematic errors. In the Fermi energy range an integral flux of F(E > 60 MeV) = (1.56 ± 0.28stat ± 0.15sys) × 10-8 cm-2 s-1 is obtained. At energies above ∼3 GeV the HE spectrum is consistent with a power-law ranging into the VHE part of the spectrum measured by H.E.S.S. with an overall spectral index Γ = 2.22 ± 0.06stat.
Conclusions: Two scenarios for the starburst nucleus are tested, in which the gas in the starburst nucleus acts as either a thin or a thick target for hadronic cosmic rays accelerated by the individual sources in the nucleus. In these two models, the level to which NGC 253 acts as a calorimeter is estimated to a range of fcal = 0.1 to 1 while accounting for the measurement uncertainties. The presented spectrum is likely to remain the most accurate measurements until the Cherenkov Telescope Array (CTA) has collected a substantial set of data towards NGC 253.
Volume
617
Start page
A73
Issn Identifier
0004-6361
Ads BibCode
2018A&A...617A..73H
Rights
open.access
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