The $γ$-ray spectrum of the core of Centaurus A as observed with H.E.S.S. and Fermi-LAT
Creators: name: Collaboration, H. E. S. S.
name: Abdalla, H.
name: Abramowski, A.
name: Aharonian, F.
name: Benkhali, F. Ait
name: Angüner, E. O.
name: Arakawa, M.
name: Armand, C.
name: Arrieta, M.
name: Backes, M.
name: Balzer, A.
name: Barnard, M.
name: Becherini, Y.
name: Tjus, J. Becker
name: Berge, D.
name: Bernhard, S.
name: Bernlöhr, K.
name: Blackwell, R.
name: Böttcher, M.
name: Boisson, C.
name: Bolmont, J.
name: Bonnefoy, S.
name: Bordas, P.
name: Bregeon, J.
name: Brun, F.
name: Brun, P.
name: Bryan, M.
name: Büchele, M.
name: Bulik, T.
name: Capasso, M.
name: Caroff, S.
name: Carosi, A.
name: Casanova, S.
name: Cerruti, M.
name: Chakraborty, N.
name: Chaves, R. C. G.
name: Chen, A.
name: Chevalier, J.
name: Colafrancesco, S.
name: Condon, B.
name: Conrad, J.
name: Davids, I. D.
name: Decock, J.
name: Deil, C.
name: Devin, J.
name: deWilt, P.
name: Dirson, L.
name: Djannati-Ataï, A.
name: Donath, A.
name: Drury, L. O'C.
name: Dyks, J.
name: Edwards, T.
name: Egberts, K.
name: Emery, G.
name: Ernenwein, J. -P.
name: Eschbach, S.
name: Farnier, C.
name: Fegan, S.
name: Fernandes, M. V.
name: Fiasson, A.
name: Fontaine, G.
name: Funk, S.
name: Füßling, M.
name: Gabici, S.
name: Gallant, Y. A.
name: Garrigoux, T.
name: Gaté, F.
name: Giavitto, G.
name: Glawion, D.
name: Glicenstein, J. F.
name: Gottschall, D.
name: Grondin, M. -H.
name: Hahn, J.
name: Haupt, M.
name: Hawkes, J.
name: Heinzelmann, G.
name: Henri, G.
name: Hermann, G.
name: Hinton, J. A.
name: Hofmann, W.
name: Hoischen, C.
name: Holch, T. L.
name: Holler, M.
name: Horns, D.
name: Ivascenko, A.
name: Iwasaki, H.
name: Jacholkowska, A.
name: Jamrozy, M.
name: Jankowsky, D.
name: Jankowsky, F.
name: Jingo, M.
name: Jouvin, L.
name: Jung-Richardt, I.
name: Kastendieck, M. A.
name: Katarzyński, K.
name: Katsuragawa, M.
name: Katz, U.
name: Kerszberg, D.
name: Khangulyan, D.
name: Khélifi, B.
name: King, J.
name: Klepser, S.
name: Klochkov, D.
name: Kluźniak, W.
name: Komin, Nu.
name: Kosack, K.
name: Krakau, S.
name: Kraus, M.
name: Krüger, P. P.
name: Laffon, H.
name: Lamanna, G.
name: Lau, J.
name: Lefaucheur, J.
name: Lemière, A.
name: Lemoine-Goumard, M.
name: Lenain, J. -P.
name: Leser, E.
name: Lohse, T.
name: Lorentz, M.
name: Liu, R.
name: López-Coto, R.
name: Lypova, I.
name: Malyshev, D.
name: Marandon, V.
name: Marcowith, A.
name: Mariaud, C.
name: Marx, R.
name: Maurin, G.
name: Maxted, N.
name: Mayer, M.
name: Meintjes, P. J.
name: Meyer, M.
name: Mitchell, A. M. W.
name: Moderski, R.
name: Mohamed, M.
name: Mohrmann, L.
name: Morå, K.
name: Moulin, E.
name: Murach, T.
name: Nakashima, S.
name: de Naurois, M.
name: Ndiyavala, H.
name: Niederwanger, F.
name: Niemiec, J.
name: Oakes, L.
name: O'Brien, P.
name: Odaka, H.
name: Ohm, S.
name: Ostrowski, M.
name: Oya, I.
name: Padovani, M.
name: Panter, M.
name: Parsons, R. D.
name: Pekeur, N. W.
name: Pelletier, G.
name: Perennes, C.
name: Petrucci, P. -O.
name: Peyaud, B.
name: Piel, Q.
name: Pita, S.
name: Poireau, V.
name: Prokhorov, D. A.
name: Prokoph, H.
name: Pühlhofer, G.
name: Punch, M.
name: Quirrenbach, A.
name: Raab, S.
name: Rauth, R.
name: Reimer, A.
name: Reimer, O.
name: Renaud, M.
name: Reyes, R. de los
name: Rieger, F.
name: Rinchiuso, L.
name: Romoli, C.
name: Rowell, G.
name: Rudak, B.
name: Rulten, C. B.
name: Sahakian, V.
name: Saito, S.
name: Sanchez, D. A.
name: Santangelo, A.
name: Sasaki, M.
name: Schlickeiser, R.
name: Schüssler, F.
name: Schulz, A.
name: Schwanke, U.
name: Schwemmer, S.
name: Seglar-Arroyo, M.
name: Seyffert, A. S.
name: Shafi, N.
name: Shilon, I.
name: Simoni, K. Shiningayamwe. R.
name: Sol, H.
name: Spanier, F.
name: Spir-Jacob, M.
name: Stawarz, Ł.
name: Steenkamp, R.
name: Stegmann, C.
name: Steppa, C.
name: Sushch, I.
name: Takahashi, T.
name: Tavernet, J. -P.
name: Tavernier, T.
name: Taylor, A. M.
name: Terrier, R.
name: Tibaldo, L.
name: Tiziani, D.
name: Tluczykont, M.
name: Trichard, C.
name: Tsirou, M.
name: Tsuji, N.
name: Tuffs, R.
name: Uchiyama, Y.
name: van der Walt, D. J.
name: van Eldik, C.
name: van Rensburg, C.
name: van Soelen, B.
name: Vasileiadis, G.
name: Veh, J.
name: Venter, C.
name: Viana, A.
name: Vincent, P.
name: Vink, J.
name: Voisin, F.
name: Völk, H. J.
name: Vuillaume, T.
name: Wadiasingh, Z.
name: Wagner, S. J.
name: Wagner, P.
name: Wagner, R. M.
name: White, R.
name: Wierzcholska, A.
name: Willmann, P.
name: Wörnlein, A.
name: Wouters, D.
name: Yang, R.
name: Zaborov, D.
name: Zacharias, M.
name: Zanin, R.
name: Zdziarski, A. A.
name: Zech, A.
name: Zefi, F.
name: Ziegler, A.
name: Zorn, J.
name: Żywucka, N.
name: collaboration, Fermi-LAT
name: Magill, J. D.
name: Buson, S.
name: Cheung, C. C.
name: Perkins, J. S.
name: Tanaka, Y.
Publisher: name: arXiv
Year: 2018
Subjects: subject: High Energy Astrophysical Phenomena (astro-ph.HE)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: Centaurus A (Cen A) is the nearest radio galaxy discovered as a very-high-energy (VHE; 100 GeV-100 TeV) $γ$-ray source by the High Energy Stereoscopic System (H.E.S.S.). It is a faint VHE $γ$-ray emitter, though its VHE flux exceeds both the extrapolation from early Fermi-LAT observations as well as expectations from a (misaligned) single-zone synchrotron-self Compton (SSC) description. The latter satisfactorily reproduces the emission from Cen A at lower energies up to a few GeV. New observations with H.E.S.S., comparable in exposure time to those previously reported, were performed and eight years of Fermi-LAT data were accumulated to clarify the spectral characteristics of the $γ$-ray emission from the core of Cen A. The results allow us for the first time to achieve the goal of constructing a representative, contemporaneous $γ$-ray core spectrum of Cen A over almost five orders of magnitude in energy. Advanced analysis methods, including the template fitting method, allow detection in the VHE range of the core with a statistical significance of 12$σ$ on the basis of 213 hours of total exposure time. The spectrum in the energy range of 250 GeV-6 TeV is compatible with a power-law function with a photon index $Γ=2.52\pm0.13_{\mathrm{stat}}\pm0.20_{\mathrm{sys}}$. An updated Fermi-LAT analysis provides evidence for spectral hardening by $ΔΓ\simeq0.4\pm0.1$ at $γ$-ray energies above $2.8^{+1.0}_{-0.6}$ GeV at a level of $4.0σ$. The fact that the spectrum hardens at GeV energies and extends into the VHE regime disfavour a single-zone SSC interpretation for the overall spectral energy distribution (SED) of the core and is suggestive of a new $γ$-ray emitting component connecting the high-energy emission above the break energy to the one observed at VHE energies.
description: Accepted for publication in A&amp;A, Abstract abridged for arXiv submission