MAGIC Collaboration, J. Aleksić, E. A. Alvarez, L. A. Antonelli, P. Antoranz, M. Asensio, M. Backes, U. Barres de Almeida, J. A. Barrio, D. Bastieri, J. Becerra González, W. Bednarek, K. Berger, E. Bernardini, A. Biland, O. Blanch, R. K. Bock, A. Boller, G. Bonnoli, D. Borla Tridon, T. Bretz, A. Cañellas, E. Carmona, A. Carosi, P. Colin, E. Colombo, J. L. Contreras, J. Cortina, L. Cossio, S. Covino, P. Da Vela, F. Dazzi, A. De Angelis, G. De Caneva, E. De Cea del Pozo, B. De Lotto, C. Delgado Mendez, A. Diago Ortega, M. Doert, A. Domínguez, D. Dominis Prester, D. Dorner, M. Doro, D. Eisenacher, D. Elsaesser, D. Ferenc, M. V. Fonseca, L. Font, C. Fruck, R. J. García López, M. Garczarczyk, D. Garrido, G. Giavitto, N. Godinović, A. González Muñoz, S. R. Gozzini, D. Hadasch, D. Häfner, A. Herrero, D. Hildebrand, J. Hose, D. Hrupec, B. Huber, F. Jankowski, T. Jogler, V. Kadenius, H. Kellermann, S. Klepser, T. Krähenbühl, J. Krause, A. La Barbera, D. Lelas, E. Leonardo, N. Lewandowska, E. Lindfors, S. Lombardi, M. López, R. López-Coto, A. López-Oramas, E. Lorenz, M. Makariev, G. Maneva, N. Mankuzhiyil, K. Mannheim, L. Maraschi, M. Mariotti, M. Martínez, D. Mazin, M. Meucci, J. M. Miranda, R. Mirzoyan, J. Moldón, A. Moralejo, P. Munar-Adrover, A. Niedzwiecki, D. Nieto, K. Nilsson, N. Nowak, R. Orito, S. Paiano, D. Paneque, R. Paoletti, S. Pardo, J. M. Paredes, S. Partini, M. A. Perez-Torres, M. Persic, M. Pilia, J. Pochon, F. Prada, P. G. Prada Moroni, E. Prandini, I. Puerto Gimenez, I. Puljak, I. Reichardt, R. Reinthal, W. Rhode, M. Ribó, J. Rico, S. Rügamer, A. Saggion, K. Saito, T. Y. Saito, M. Salvati, K. Satalecka, V. Scalzotto, V. Scapin, C. Schultz, T. Schweizer, S. N. Shore, A. Sillanpää, J. Sitarek, I. Snidaric, D. Sobczynska, F. Spanier, S. Spiro, V. Stamatescu, A. Stamerra, B. Steinke, J. Storz, N. Strah, S. Sun, T. Surić, L. Takalo, H. Takami, F. Tavecchio, P. Temnikov, T. Terzić, D. Tescaro, M. Teshima, O. Tibolla, D. F. Torres, A. Treves, M. Uellenbeck, P. Vogler, R. M. Wagner, Q. Weitzel, V. Zabalza, F. Zandanel, R. Zanin
The W51 complex hosts the supernova remnant W51C which is known to interact
with the molecular clouds in the star forming region W51B. In addition, a
possible pulsar wind nebula CXO J192318.5+140305 was found likely associated
with the supernova remnant. Gamma-ray emission from this region was discovered
by Fermi/LAT (between 0.2 and 50 GeV) and H.E.S.S. (>1 TeV). The spatial
distribution of the events could not be used to pinpoint the location of the
emission among the pulsar wind nebula, the supernova remnant shell and/or the
molecular cloud. However, the modeling of the spectral energy distribution
presented by the Fermi/LAT collaboration suggests a hadronic emission
mechanism. We performed observations of the W51 complex with the MAGIC
telescopes for more than 50 hours. The good angular resolution in the medium
(few hundred GeV) to high (above 1 TeV) energies allow us to perform
morphological studies. We detect an extended emission of very-high-energy gamma
rays, with a significance of 11 standard deviations. We extend the spectrum
from the highest Fermi/LAT energies to \sim 5 TeV and find that it follows a
single power law with an index of 2.58 \pm 0.07stat \pm 0.22syst . The main
part of the emission coincides with the shocked cloud region, while we find a
feature extending towards the pulsar wind nebula. The possible contribution of
the pulsar wind nebula, assuming a point-like source, shows no dependence on
energy and it is about 20% of the overall emission. The broad band spectral
energy distribution can be explained with a hadronic model that implies proton
acceleration above 100 TeV. This result, together with the morphology of the
source, tentatively suggests that we observe ongoing acceleration of ions in
the interaction zone between supernova remnant and cloud. These results shed
light on the long-standing problem of the origin of galactic cosmic rays.
View original:
http://arxiv.org/abs/1201.4074
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