Detection of very high energy radiation from the BL lacertae object PG 1553+113 with the MAGIC telescope

Albert, J.; Aliu, E.; Anderhub, H.; Antoranz, P.; Armada, A.; Baixeras, C.; Barrio, J. A.; Bartko, H.; Bastieri, D.; Becker, J.; Bednarek, W.; Berger, K.; Bigongiari, C.; Biland, A.; Bock, R. K.; Bordas, P.; Bosch Raman, V.; Bretz, T.; Britvitch, I.; Camara, M.; Carmona, E.; Chilingarian, A.; Ciprini, S.; Coarasa, J. A.; Commichau, S.; Contreras, J. L.; Cortina, J.; Curtef, V.; Danielyan, V.; Dazzi, F.; Angelis, A. D.; Reyes, R. D. L.; Lotto, B. D.; Domingo Santamaria, E.; Dorner, D.; Doro, M.; Errando, M.; Fagiolini, M.; Ferenc, D.; Fernandez, E.; Firpo, R.; Flix, J.; Fonseca, M. V.; Font, L.; Fuchs, M.; Galante, N.; Garczarczyk, M.; Gaug, M.; Giller, M.; Goebel, F.; Hakobyan, D.; Hayashida, M.; Hengstebeck, T.; Hohne, D.; Hose, J.; Hsu, C. C.; Jacon, P.; Jogler, T.; Kalekin, O.; Kosyra, R.; Kranich, D.; Kritzer, R.; Laille, A.; Liebing, P.; Lindfors, E.; Lombardi, S.; Longo, Francesco; Lopez, J.; Lopez, M.; Lorenz, E.; Majumdar, P.; Maneva, G.; Mannheim, K.; Mansutti, O.; Mariotti, M.; Martinez, M.; Mazin, D.; Merck, C.; Meucci, M.; Meyer, M.; Miranda, J. M.; Mirzoyan, R.; Mizobuchi, S.; Moralejo, A.; Nilsson, K.; Ninkovic, J.; Ona Wilhelmi, E.; Otte, N.; Oya, I.; Paneque, D.; Paoletti, R.; Paredes, J. M.; Pasanen, M.; Pascoli, D.; Pauss, F.; Pegna, R.; Persic, M.; Peruzzo, L.; Piccioli, A.; Poller, M.; Puchades, N.; Prandini, E.; Raymers, A.; Rhode, W.; Ribo, M.; Rico, J.; Rissi, M.; Robert, A.; Rugamer, S.; Saggion, A.; Sanchez, A.; Sartori, P.; Scalzotto, V.; Scapin, V.; Schmitt, R.; Schweizer, T.; Shayduk, M.; Shinozaki, K.; Sidro, N.; Sillanpaa, A.; Sobczynska, D.; Stamerra, A.; Stark, L. S.; Takalo, L.; Temnikov, P.; Tescaro, D.; Teshima, M.; Tonello, N.; Torres, D. F.; Turini, N.; Vankov, H.; Vitale, V.; Wagner, R. M.; Wibig, T.; Wittek, W.; Zanin, R.; Zapatero, J.

In 2005 and 2006, the MAGIC telescope observed very high energy gamma-ray emission from the distant BL Lac object PG 1553 + 113. The overall significance of the signal was 8.8 sigma for 18.8 hr of observation time. The light curve shows no significant flux variations on a daily timescale; the flux level during 2005 was, however, significantly higher compared to 2006. The differential energy spectrum between similar to 90 and 500 GeV is well described by a power law with photon index. Gamma = 4.2 +/- 0.3. The combined 2005 and 2006 energy spectrum provides an upper limit of z = 0.74 on the redshift of the object.