Constraining Cosmic Rays and Magnetic Fields in the Perseus Galaxy Cluster with TeV observations by the MAGIC telescopes
Abstract
Galaxy clusters are being assembled today in the most energetic phase of hierarchical structure formation which manifests itself in powerful shocks that contribute to a substantial energy density of cosmic rays (CRs). Hence, clusters are expected to be luminous gamma-ray emitters since they also act as energy reservoirs for additional CR sources, such as active galactic nuclei and supernova-driven galactic winds. To detect the gamma-ray emission from CR interactions with the ambient cluster gas, we conducted the deepest to date observational campaign targeting a galaxy cluster at very high-energy gamma-rays and observed the Perseus cluster with the MAGIC Cherenkov telescopes for a total of ~85 hr of effective observing time. This campaign resulted in the detection of the central radio galaxy NGC 1275 at energies E > 100 GeV with a very steep energy spectrum. Here, we restrict our analysis to energies E > 630 GeV and detect no significant gamma-ray excess. This constrains the average CR-to-thermal pressure ratio to be <= 1-2%, depending on assumptions and the model for CR emission. Comparing these gamma-ray upper limits to predictions from cosmological cluster simulations that include CRs constrains the maximum CR acceleration efficiency at structure formation shocks to be < 50%. Alternatively, this may argue for non-negligible CR transport processes such as CR streaming and diffusion into the outer cluster regions. Finally, we derive lower limits on the magnetic field distribution assuming that the Perseus radio mini-halo is generated by secondary electrons/positrons that are created in hadronic CR interactions: assuming a spectrum of E^-2.2 around TeV energies as implied by cluster simulations, we limit the central magnetic field to be > 4-9 microG, depending on the rate of decline of the magnetic field strength toward larger radii.
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Cite
@article{arxiv.1111.5544,
title = {Constraining Cosmic Rays and Magnetic Fields in the Perseus Galaxy Cluster with TeV observations by the MAGIC telescopes},
author = {MAGIC Collaboration and J. Aleksić and E. A. Alvarez and L. A. Antonelli and P. Antoranz and M. Asensio and M. Backes and U. Barres de Almeida and J. A. Barrio and D. Bastieri and J. Becerra González and W. Bednarek and A. Berdyugin and K. Berger and E. Bernardini and A. Biland and O. Blanch and R. K. Bock and A. Boller and G. Bonnoli and D. Borla Tridon and I. Braun and T. Bretz and A. Cañellas and E. Carmona and A. Carosi and P. Colin and E. Colombo and J. L. Contreras and J. Cortina and L. Cossio and S. Covino and F. Dazzi and A. De Angelis and G. De Caneva and E. De Cea del Pozo and B. De Lotto and C. Delgado Mendez and A. Diago Ortega and M. Doert and A. Domínguez and D. Dominis Prester and D. Dorner and M. Doro and D. Eisenacher and D. Elsaesser and D. Ferenc and M. V. Fonseca and L. Font and C. Fruck and R. J. García López and M. Garczarczyk and D. Garrido and G. Giavitto and N. Godinović and S. R. Gozzini and D. Hadasch and D. Häfner and A. Herrero and D. Hildebrand and D. Höhne-Mönch and J. Hose and D. Hrupec and T. Jogler and H. Kellermann and S. Klepser and T. Krähenbühl and J. Krause and J. Kushida and A. La Barbera and D. Lelas and E. Leonardo and N. Lewandowska and E. Lindfors and S. Lombardi and M. López and R. López-Coto and A. López-Oramas and E. Lorenz and M. Makariev and G. Maneva and N. Mankuzhiyil and K. Mannheim and L. Maraschi and M. Mariotti and M. Martínez and D. Mazin and M. Meucci and J. M. Miranda and R. Mirzoyan and J. Moldón and A. Moralejo and P. Munar-Adrover and A. Niedzwiecki and D. Nieto and K. Nilsson and N. Nowak and R. Orito and S. Paiano and D. Paneque and R. Paoletti and S. Pardo and J. M. Paredes and S. Partini and M. A. Perez-Torres and M. Persic and L. Peruzzo and M. Pilia and J. Pochon and F. Prada and P. G. Prada Moroni and E. Prandini and I. Puerto Gimenez and I. Puljak and I. Reichardt and R. Reinthal and W. Rhode and M. Ribó and J. Rico and S. Rügamer and A. Saggion and K. Saito and T. Y. Saito and M. Salvati and K. Satalecka and V. Scalzotto and V. Scapin and C. Schultz and T. Schweizer and M. Shayduk and S. N. Shore and A. Sillanpää and J. Sitarek and I. Snidaric and D. Sobczynska and F. Spanier and S. Spiro and V. Stamatescu and A. Stamerra and B. Steinke and J. Storz and N. Strah and S. Sun and T. Surić and L. Takalo and H. Takami and F. Tavecchio and P. Temnikov and T. Terzić and D. Tescaro and M. Teshima and O. Tibolla and D. F. Torres and A. Treves and M. Uellenbeck and H. Vankov and P. Vogler and R. M. Wagner and Q. Weitzel and V. Zabalza and F. Zandanel and R. Zanin and C. Pfrommer and A. Pinzke},
journal= {arXiv preprint arXiv:1111.5544},
year = {2012}
}
Comments
Corresponding authors are F. Zandanel, C. Pfrommer, P. Colin, A. Pinzke and S. Lombardi. Accepted for publication in A&A on 06/03/2012