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  • Detection of very-high ener...
    Aleksić, J.; Alvarez, E. A.; Antoranz, P.; Asensio, M.; Barres de Almeida, U.; Barrio, J. A.; Bastieri, D.; Becerra González, J.; Bednarek, W.; Biland, A.; Bonnoli, G.; Borla Tridon, D.; Bretz, T.; Cañellas, A.; Carmona, E.; Colin, P.; Contreras, J. L.; Da Vela, P.; Dazzi, F.; De Angelis, A.; De Caneva, G.; Delgado Mendez, C.; Doert, M.; Domínguez, A.; Doro, M.; Eisenacher, D.; Elsaesser, D.; Ferenc, D.; Font, L.; Garczarczyk, M.; Giavitto, G.; Godinović, N.; Hadasch, D.; Herrero, A.; Hildebrand, D.; Höhne-Mönch, D.; Hose, J.; Huber, B.; Jogler, T.; Kadenius, V.; Krähenbühl, T.; Krause, J.; Lelas, D.; Leonardo, E.; Lindfors, E.; Lombardi, S.; López-Coto, R.; Lorenz, E.; Makariev, M.; Maneva, G.; Mannheim, K.; Maraschi, L.; Mariotti, M.; Martínez, M.; Mazin, D.; Miranda, J. M.; Moralejo, A.; Munar-Adrover, P.; Nieto, D.; Nilsson, K.; Paiano, S.; Paneque, D.; Paoletti, R.; Paredes, J. M.; Partini, S.; Perez-Torres, M. A.; Persic, M.; Pilia, M.; Pochon, J.; Prada Moroni, P. G.; Prandini, E.; Puerto Gimenez, I.; Puljak, I.; Reichardt, I.; Rhode, W.; Ribó, M.; Rico, J.; Rügamer, S.; Saggion, A.; Saito, K.; Saito, T. Y.; Schultz, C.; Schweizer, T.; Shore, S. N.; Spanier, F.; Stamatescu, V.; Steinke, B.; Strah, N.; Sun, S.; Takalo, L.; Takami, H.; Tavecchio, F.; Temnikov, P.; Tescaro, D.; Teshima, M.; Tibolla, O.; Treves, A.; Uellenbeck, M.; Weitzel, Q.; Pfrommer, C.

    Astronomy & astrophysics, 03/2012, Letnik: 539
    Journal Article

    We report on the detection of very-high energy (VHE, E > 100 GeV) γ-ray emission from NGC 1275, the central radio galaxy of the Perseus cluster of galaxies. The source has been detected by the MAGIC telescopes with a statistical significance of 6.6σ above 100 GeV in 46 h of stereo observations carried out between August 2010 and February 2011. The measured differential energy spectrum between 70 GeV and 500 GeV can be described by a power law with a steep spectral index of Γ =  −4.1 ± 0.7stat ± 0.3syst, and the average flux above 100 GeV is Fγ = (1.3 ± 0.2stat ± 0.3syst) × 10-11   cm-2   s-1. These results, combined with the power-law spectrum measured in the first two years of observations by the Fermi-LAT above 100 MeV, with a spectral index of Γ ≃  − 2.1, strongly suggest the presence of a break or cut-off around tens of GeV in the NGC 1275 spectrum. The light curve of the source above 100 GeV does not show hints of variability on a month time scale. Finally, we report on the nondetection in the present data of the radio galaxy IC 310, previously discovered by the Fermi-LAT and MAGIC. The derived flux upper limit FU.L.γ (>300 GeV) = 1.2 × 10-12 cm-2 s-1 is a factor  ~ 3 lower than the mean flux measured by MAGIC between October 2009 and February 2010, thus confirming the year time-scale variability of the source at VHE.