PG 1553+113: five years of observations with MAGIC

• Published in: arXiv.org 2012-01
• Main Authors: Antoranz, P, Asensio, M, Backes, M, Barrio, J A, Bastieri, D, J Becerra González, Berdyugin, A, Berger, K, Bernardini, E, Biland, A, Blanch, O, Bock, R K, Boller, A, Bonnoli, G, Braun, I, Bretz, T, Cañellas, A, Carmona, E, Carosi, A, Colin, P, Cortina, J, Dazzi, F, De Angelis, A, De Caneva, G, C Delgado Mendez, A Diago Ortega, Doert, M, D Dominis Prester, Ferenc, D, Fonseca, M V, Garczarczyk, M, Garrido, D, Giavitto, G, Herrero, A, Hildebrand, D, Höhne-Mönch, D, Hose, J, Hrupec, D, Huber, B, Jogler, T, Kellermann, H, Klepser, S, Krähenbühl, T, La Barbera, A, Lindfors, E, López, M, Mankuzhiyil, N, Maraschi, L, Mariotti, M, Mazin, D, Miranda, J M, Mirzoyan, R, Miyamoto, H, Moldón, J, Moralejo, A, Nieto, D, Nilsson, K, Orito, R, Oya, I, Paneque, D, Paoletti, R, Pardo, S, Paredes, J M, Partini, S, Pasanen, M, Perez-Torres, M A, Persic, M, Pilia, M, Pochon, J, Prada, F, Prada Moroni, P G, Puljak, I, Reichardt, I, Reinthal, R, Rhode, W, Saggion, A, Saito, K, Scalzotto, V, Shayduk, M, Sitarek, J, Spanier, F, Spiro, S, Stamatescu, V, Steinke, B, Strah, N, Takalo, L, Temnikov, P, Terzić, T, Tescaro, D, Teshima, M, Tibolla, O, Torres, D F, Vogler, P, Wagner, R M, Weitzel, Q, Zabalza, V, Zandanel, F, Zanin, R, Buson, S, Horan, D
• Format: Article
• Language: English
• Subjects: BL Lacertae objects; Crab nebula; Flux; Gamma rays; Physical properties; Spectral energy distribution
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.1101.2764

We present the results of five years (2005-2009) of MAGIC observations of the BL Lac object PG 1553+113 at very high energies (VHEs, E > 100 GeV). Power law fits of the individual years are compatible with a steady mean photon index \Gamma = 4.27 \(\pm\) 0.14. In the last three years of data, the flux level above 150 GeV shows a clear variability (probability of constant flux < 0.001%). The flux variations are modest, lying in the range from 4% to 11% of the Crab Nebula flux. Simultaneous optical data also show only modest variability that seems to be correlated with VHE gamma ray variability. We also performed a temporal analysis of (all available) simultaneous Fermi/LAT data of PG 1553+113 above 1 GeV, which reveals hints of variability in the 2008-2009 sample. Finally, we present a combination of the mean spectrum measured at very high energies with archival data available for other wavelengths. The mean spectral energy distribution can be modeled with a one-zone Synchrotron Self Compton (SSC) model, which gives the main physical parameters governing the VHE emission in the blazar jet.