Acceleration of petaelectronvolt protons in the Galactic Centre

H. E. S. S. collaboration, :, A. Abramowski, F. Aharonian, F. Ait Benkhali, A. G. Akhperjanian, E. O. Angüner, M. Backes, A. Balzer, Y. Becherini, J. Becker Tjus, D. Berge, S. Bernhard, K. Bernlöhr, E. Birsin, R. Blackwell, M. Böttcher, C. Boisson, J. Bolmont, P. Bordas, J. Bregeon, F. Brun, P. Brun, M. Bryan, T. Bulik, J. Carr, S. Casanova, N. Chakraborty, R. Chalme-Calvet, R. C. G. Chaves, A. Chen, M. Chrétien, S. Colafrancesco, G. Cologna, J. Conrad, C. Couturier, Y. Cui, I. D. Davids, B. Degrange, C. Deil, P. deWilt, A. Djannati-Ataï, W. Domainko, A. Donath, L. O'C. Drury, G. Dubus, K. Dutson, J. Dyks, M. Dyrda, T. Edwards, K. Egberts, P. Eger, J. -P. Ernenwein, P. Espigat, C. Farnier, S. Fegan, F. Feinstein, M. V. Fernandes, D. Fernandez, A. Fiasson, G. Fontaine, A. Förster, M. Füßling, S. Gabici, M. Gajdus, Y. A. Gallant, T. Garrigoux, G. Giavitto, B. Giebels, J. F. Glicenstein, D. Gottschall, A. Goyal, M. -H. Grondin, M. Grudzińska, D. Hadasch, S. Häffner, J. Hahn, J. Hawkes, G. Heinzelmann, G. Henri, G. Hermann, O. Hervet, A. Hillert, J. A. Hinton, W. Hofmann, P. Hofverberg, C. Hoischen, M. Holler, D. Horns, A. Ivascenko, A. Jacholkowska, M. Jamrozy, M. Janiak, F. Jankowsky, I. Jung-Richardt, M. A. Kastendieck, K. Katarzyński, U. Katz, D. Kerszberg, B. Khélifi, M. Kieffer, S. Klepser, D. Klochkov, W. Kluźniak, D. Kolitzus, Nu. Komin, K. Kosack, S. Krakau, F. Krayzel, P. P. Krüger, H. Laffon, G. Lamanna, J. Lau, J. Lefaucheur, V. Lefranc, A. Lemiére, M. Lemoine-Goumard, J. -P. Lenain, T. Lohse, A. Lopatin, C. -C. Lu, R. Lui, V. Marandon, A. Marcowith, C. Mariaud, R. Marx, G. Maurin, N. Maxted, M. Mayer, P. J. Meintjes, U. Menzler, M. Meyer, A. M. W. Mitchell, R. Moderski, M. Mohamed, K. Morå, E. Moulin, T. Murach, M. de Naurois, J. Niemiec, L. Oakes, H. Odaka, S. Öttl, S. Ohm, B. Opitz, M. Ostrowski, I. Oya, M. Panter, R. D. Parsons, M. Paz Arribas, N. W. Pekeur, G. Pelletier, P. -O. Petrucci, B. Peyaud, S. Pita, H. Poon, H. Prokoph, G. Pühlhofer, M. Punch, A. Quirrenbach, S. Raab, I. Reichardt, A. Reimer, O. Reimer, M. Renaud, R. de los Reyes, F. Rieger, C. Romoli, S. Rosier-Lees, G. Rowell, B. Rudak, C. B. Rulten, V. Sahakian, D. Salek, D. A. Sanchez, A. Santangelo, M. Sasaki, R. Schlickeiser, F. Schüssler, A. Schulz, U. Schwanke, S. Schwemmer, A. S. Seyffert, R. Simoni, H. Sol, F. Spanier, G. Spengler, F. Spies, Ł. Stawarz, R. Steenkamp, C. Stegmann, F. Stinzing, K. Stycz, I. Sushch, J. -P. Tavernet, T. Tavernier, A. M. Taylor, R. Terrier, M. Tluczykont, C. Trichard, R. Tuffs, K. Valerius, J. van der Walt, C. van Eldik, B. van Soelen, G. Vasileiadis, J. Veh, C. Venter, A. Viana, P. Vincent, J. Vink, F. Voisin, H. J. Völk, T. Vuillaume, S. J. Wagner, P. Wagner, R. M. Wagner, M. Weidinger, Q. Weitzel, R. White, A. Wierzcholska, P. Willmann, A. Wörnlein, D. Wouters, R. Yang, V. Zabalza, D. Zaborov, M. Zacharias, A. A. Zdziarski, A. Zech, F. Zefi, N. Żywucka

Published 2016-03-24Version 1

Galactic cosmic rays reach energies of at least a few Peta-electronvolts (1 PeV =$10^\mathbf{15}$ electron volts). This implies our Galaxy contains PeV accelerators (PeVatrons), but all proposed models of Galactic cosmic-ray accelerators encounter non-trivial difficulties at exactly these energies. Tens of Galactic accelerators capable of accelerating particle to tens of TeV (1 TeV =$10^\mathbf{12}$ electron volts) energies were inferred from recent gamma-ray observations. None of the currently known accelerators, however, not even the handful of shell-type supernova remnants commonly believed to supply most Galactic cosmic rays, have shown the characteristic tracers of PeV particles: power-law spectra of gamma rays extending without a cutoff or a spectral break to tens of TeV. Here we report deep gamma-ray observations with arcminute angular resolution of the Galactic Centre regions, which show the expected tracer of the presence of PeV particles within the central 10~parsec of the Galaxy. We argue that the supermassive black hole Sagittarius A* is linked to this PeVatron. Sagittarius A* went through active phases in the past, as demonstrated by X-ray outbursts and an outflow from the Galactic Centre. Although its current rate of particle acceleration is not sufficient to provide a substantial contribution to Galactic cosmic rays, Sagittarius A* could have plausibly been more active over the last $\gtrsim 10^{6-7}$ years, and therefore should be considered as a viable alternative to supernova remnants as a source of PeV Galactic cosmic rays.