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The gamma-ray spectrum of the core of Centaurus A as observed with HESS and Fermi-LAT

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posted on 2019-09-18, 11:23 authored by H Abdalla, A Abramowski, F Aharonian, FA Benkhali, EO Anguner, M Arakawa, C Armand, M Arrieta, M Backes, A Balzer, M Barnard, Y Becherini, JB Tjus, D Berge, S Bernhard, K Bernloehr, R Blackwell, M Bottcher, C Boisson, J Bolmont, S Bonnefoy, P Bordas, J Bregeon, F Brun, P Brun, M Bryan, M Buechele, T Bulik, M Capasso, S Caroff, A Carosi, S Casanova, M Cerruti, N Chakraborty, RCG Chaves, A Chen, J Chevalier, S Colafrancesco, B Condon, J Conrad, ID Davids, J Decock, C Deil, J Devin, P deWilt, L Dirson, A Djannati-Atai, A Donath, LO Drury, J Dyks, T Edwards, K Egberts, G Emery, J-P Ernenwein, S Eschbach, C Farnier, S Fegan, M Fernandes, A Fiasson, G Fontaine, S Funk, M Fuessling, S Gabici, YA Gallant, T Garrigoux, F Gate, G Giavitto, D Glawion, JF Glicenstein, D Gottschall, M-H Grondin, J Hahn, M Haupt, J Hawkes, G Heinzelmann, G Henri, G Hermann, JA Hinton, W Hofmann, C Hoischen, TL Holch, M Holler, D Horns, A Ivascenko, H Iwasaki, A Jacholkowska, M Jamrozy, D Jankowsky, F Jankowsky, M Jingo, L Jouvin, I Jung-Richardt, MA Kastendieck, K Katarzynski, M Katsuragawa, U Katz, D Kerszberg, D Khangulyan, B Khelifi, J King, S Klepser, D Klochkov, W Kluzniak, N Komin, K Kosack, S Krakau, M Kraus, PP Kruger, H Laffon, G Lamanna, J Lau, J Lefaucheur, A Lemiere, M Lemoine-Goumard, J-P Lenain, E Leser, T Lohse, M Lorentz, R Liu, R Lopez-Coto, I Lypova, D Malyshev, V Marandon, A Marcowith, C Mariaud, R Marx, G Maurin, N Maxted, M Mayer, PJ Meintjes, M Meyer, AMW Mitchell, R Moderski, M Mohamed, L Mohrmann, K Mora, E Moulin, T Murach, S Nakashima, M de Naurois, H Ndiyavala, F Niederwanger, J Niemiec, L Oakes, P O'Brien, H Odaka, S Ohm, M Ostrowski, I Oya, M Padovani, M Panter, RD Parsons, NW Pekeur, G Pelletier, C Perennes, P-O Petrucci, B Peyaud, Q Piel, S Pita, V Poireau, DA Prokhorov, H Prokoph, G Puehlhofer, M Punch, A Quirrenbach, S Raab, R Rauth, A Reimer, O Reimer, M Renaud, R de los Reyes, F Rieger, L Rinchiuso, C Romoli, G Rowell, B Rudak, CB Rulten, V Sahakian, S Saito, DA Sanchez, A Santangelo, M Sasaki, R Schlickeiser, F Schussler, A Schulz, U Schwanke, S Schwemmer, M Seglar-Arroyo, AS Seyffert, N Shafi, I Shilon, K Shiningayamwe, R Simoni, H Sol, F Spanier, M Spir-Jacob, L Stawarz, R Steenkamp, C Stegmann, C Steppa, I Sushch, T Takahashi, J-P Tavernet, T Tavernier, AM Taylor, R Terrier, L Tibaldo, D Tiziani, M Tluczykont, C Trichard, M Tsirou, N Tsuji, R Tuffs, Y Uchiyama, DJ van der Walt, C van Eldik, C van Rensburg, B van Soelen, G Vasileiadis, J Veh, C Venter, A Viana, P Vincent, J Vink, F Voisin, HJ Voelk, T Vuillaume, Z Wadiasingh, SJ Wagner, P Wagner, RM Wagner, R White, A Wierzcholska, P Willmann, A Woernlein, D Wouters, R Yang, D Zaborov, M Zacharias, R Zanin, AA Zdziarski, A Zech, F Zefi, A Ziegler, J Zorn, N Zywucka, JD Magill, S Buson, CC Cheung, JS Perkins, Y Tanaka
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 12σ 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 ± 0.13stat ± 0.20sys. An updated Fermi-LAT analysis provides evidence for spectral hardening by ∆Γ ' 0.4 ± 0.1 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. The absence of significant variability at both GeV and TeV energies does not yet allow disentanglement of the physical nature of this component, though a jet-related origin is possible and a simple two-zone SED model fit is provided to this end.

Funding

The support of the Namibian authorities and of the University of Namibia in facilitating the construction and operation of H.E.S.S. is gratefully acknowledged, as is the support by the German Ministry for Education and Research (BMBF), the Max Planck Society, the German Research Foundation (DFG), the Helmholtz Association, the Alexander von Humboldt Foundation, the French Ministry of Higher Education, Research and Innovation, the Centre National de la Recherche Scientifique (CNRS/IN2P3 and CNRS/INSU), the Commissariat à l’énergie atomique et aux énergies alternatives (CEA), the U.K. Science and Technology Facilities Council (STFC), the Knut and Alice Wallenberg Foundation, the National Science Centre, Poland grant no. 2016/22/M/ST9/00382, the South African Department of Science and Technology and National Research Foundation, the University of Namibia, the National Commission on Research, Science & Technology of Namibia (NCRST), the Austrian Federal Ministry of Education, Science and Research and the Austrian Science Fund (FWF), the Australian Research Council (ARC), the Japan Society for the Promotion of Science, and by the University of Amsterdam. We appreciate the excellent work of the technical support staff in Berlin, Zeuthen, Heidelberg, Palaiseau, Paris, Saclay, Tübingen, and in Namibia in the construction and operation of the equipment. This work benefited from services provided by the H.E.S.S. Virtual Organisation, supported by the national resource providers of the EGI Federation. Fermi-LAT Collaboration acknowledges generous ongoing support from a number of agencies and institutes that have supported both the development and the operation of the LAT as well as scientific data analysis. These include the National Aeronautics and Space Administration and the Department of Energy in the United States, the Commissariat à l’Énergie Atomique and the Centre National de la Recherche Scientifique/Institut National de Physique Nucléaire et de Physi

History

Citation

Astronomy and Astrophysics, 2018, 619, A71

Author affiliation

/Organisation/COLLEGE OF SCIENCE AND ENGINEERING/Department of Physics and Astronomy

Version

  • VoR (Version of Record)

Published in

Astronomy and Astrophysics

Publisher

EDP Sciences for European Southern Observatory (ESO)

issn

1432-0746

Acceptance date

2018-07-05

Copyright date

2018

Available date

2019-09-18

Publisher version

https://www.aanda.org/articles/aa/abs/2018/11/aa32640-18/aa32640-18.html

Language

en