Probing the very high energy γ-ray spectral curvature in the blazar PG 1553+113 with the MAGIC telescopes
J. AleksićIFAE, Campus UAB, E-08193 Bellaterra, SpainS. AnsoldiUniversità di Udine, and INFN Trieste, I-33100 Udine, ItalyL. A. AntonelliINAF National Institute for Astrophysics, I-00136 Rome, ItalyP. AntoranzUniversità di Siena, and INFN Pisa, I-53100 Siena, ItalyA. BabicCroatian MAGIC Consortium, Rudjer Boskovic Institute, University of Rijeka and University of Split, HR-10000 Zagreb, CroatiaP. BangaleMax-Planck-Institut für Physik, D-80805 München, GermanyJ. A. BarrioUniversidad Complutense, E-28040 Madrid, SpainJ. Becerra GonzálezInst. de Astrofísica de Canarias, E-38200 La Laguna, Tenerife, SpainW. BednarekUniversity of Łódź, PL-90236 Lodz, PolandE. BernardiniDeutsches Elektronen-Synchrotron (DESY), D-15738 Zeuthen, GermanyB. BiasuzziUniversità di Udine, and INFN Trieste, I-33100 Udine, ItalyA. BilandETH Zurich, CH-8093 Zurich, SwitzerlandO. BlanchIFAE, Campus UAB, E-08193 Bellaterra, SpainS. BonnefoyUniversidad Complutense, E-28040 Madrid, SpainG. BonnoliINAF National Institute for Astrophysics, I-00136 Rome, ItalyF. BorracciMax-Planck-Institut für Physik, D-80805 München, GermanyT. BretzUniversität Würzburg, D-97074 Würzburg, GermanyE. CarmonaCentro de Investigaciones Energéticas, Medioambientales y Tecnológicas, E-28040 Madrid, SpainA. CarosiINAF National Institute for Astrophysics, I-00136 Rome, ItalyP. ColinMax-Planck-Institut für Physik, D-80805 München, GermanyE. ColomboInst. de Astrofísica de Canarias, E-38200 La Laguna, Tenerife, SpainJ. L. ContrerasUniversidad Complutense, E-28040 Madrid, SpainJ. CortinaIFAE, Campus UAB, E-08193 Bellaterra, SpainS. CovinoINAF National Institute for Astrophysics, I-00136 Rome, ItalyP. Da VelaUniversità di Siena, and INFN Pisa, I-53100 Siena, ItalyF. DazziMax-Planck-Institut für Physik, D-80805 München, GermanyA. De AngelisUniversità di Udine, and INFN Trieste, I-33100 Udine, ItalyG. De CanevaDeutsches Elektronen-Synchrotron (DESY), D-15738 Zeuthen, GermanyB. De LottoUniversità di Udine, and INFN Trieste, I-33100 Udine, ItalyE. de Oña WilhelmiInstitute of Space Sciences, E-08193 Barcelona, SpainC. Delgado MendezCentro de Investigaciones Energéticas, Medioambientales y Tecnológicas, E-28040 Madrid, SpainD. Dominis PresterCroatian MAGIC Consortium, Rudjer Boskovic Institute, University of Rijeka and University of Split, HR-10000 Zagreb, CroatiaD. DornerUniversität Würzburg, D-97074 Würzburg, GermanyM. DoroUniversità di Padova and INFN, I-35131 Padova, ItalyS. EineckeTechnische Universität Dortmund, D-44221 Dortmund, GermanyD. EisenacherUniversität Würzburg, D-97074 Würzburg, GermanyD. ElsäesserCentro de Investigaciones Energéticas, Medioambientales y Tecnológicas, E-28040 Madrid, SpainD. FidalgoUniversidad Complutense, E-28040 Madrid, SpainM. V. FonsecaUniversidad Complutense, E-28040 Madrid, SpainL. FontUnitat de Física de les Radiacions, Departament de Física, and CERES-IEEC, Universitat Autònoma de Barcelona, E-08193 Bellaterra, SpainK. FrantzenTechnische Universität Dortmund, D-44221 Dortmund, GermanyC. FruckMax-Planck-Institut für Physik, D-80805 München, GermanyD. GalindoUniversitat de Barcelona, ICC, IEEC-UB, E-08028 Barcelona, SpainR. J. García LópezInst. de Astrofísica de Canarias, E-38200 La Laguna, Tenerife, SpainM. GarczarczykDeutsches Elektronen-Synchrotron (DESY), D-15738 Zeuthen, GermanyD. Garrido TerratsUnitat de Física de les Radiacions, Departament de Física, and CERES-IEEC, Universitat Autònoma de Barcelona, E-08193 Bellaterra, SpainM. GaugUnitat de Física de les Radiacions, Departament de Física, and CERES-IEEC, Universitat Autònoma de Barcelona, E-08193 Bellaterra, SpainN. GodinovićCroatian MAGIC Consortium, Rudjer Boskovic Institute, University of Rijeka and University of Split, HR-10000 Zagreb, CroatiaAlfonso MuñozIFAE, Campus UAB, E-08193 Bellaterra, SpainS. R. GozziniDeutsches Elektronen-Synchrotron (DESY), D-15738 Zeuthen, GermanyD. HadaschTechnische Universität Dortmund, D-44221 Dortmund, GermanyY. HanabataJapanese MAGIC Consortium, Division of Physics and Astronomy, Kyoto University, JapanM. HayashidaJapanese MAGIC Consortium, Division of Physics and Astronomy, Kyoto University, JapanJuan Manuel HerreraInst. de Astrofísica de Canarias, E-38200 La Laguna, Tenerife, SpainD. HildebrandETH Zurich, CH-8093 Zurich, SwitzerlandJ. HoseMax-Planck-Institut für Physik, D-80805 München, GermanyDario HrupecCroatian MAGIC Consortium, Rudjer Boskovic Institute, University of Rijeka and University of Split, HR-10000 Zagreb, CroatiaW. IdecUniversity of Łódź, PL-90236 Lodz, PolandV. KadeniusFinnish MAGIC Consortium, Tuorla Observatory, University of Turku and Department of Physics, University of Oulu, FinlandH. KellermannMax-Planck-Institut für Physik, D-80805 München, GermanyM. L. KnoetigETH Zurich, CH-8093 Zurich, SwitzerlandK. KodaniJapanese MAGIC Consortium, Division of Physics and Astronomy, Kyoto University, JapanY. KonnoJapanese MAGIC Consortium, Division of Physics and Astronomy, Kyoto University, JapanJ. KrauseMax-Planck-Institut für Physik, D-80805 München, GermanyHiroaki KuboJapanese MAGIC Consortium, Division of Physics and Astronomy, Kyoto University, JapanJ. KushidaJapanese MAGIC Consortium, Division of Physics and Astronomy, Kyoto University, JapanA. La BarberaINAF National Institute for Astrophysics, I-00136 Rome, ItalyD. LelasCroatian MAGIC Consortium, Rudjer Boskovic Institute, University of Rijeka and University of Split, HR-10000 Zagreb, CroatiaN. LewandowskaUniversität Würzburg, D-97074 Würzburg, GermanyE. LindforsFinnish MAGIC Consortium, Tuorla Observatory, University of Turku and Department of Physics, University of Oulu, FinlandS. LombardiINAF National Institute for Astrophysics, I-00136 Rome, ItalyF. LongoUniversità di Udine, and INFN Trieste, I-33100 Udine, ItalyM. LópezUniversidad Complutense, E-28040 Madrid, SpainR. López-CotoIFAE, Campus UAB, E-08193 Bellaterra, SpainA. López-OramasIFAE, Campus UAB, E-08193 Bellaterra, SpainE. LorenzMax-Planck-Institut für Physik, D-80805 München, GermanyIrene Albarrán LozanoUniversidad Complutense, E-28040 Madrid, SpainM. MakarievInstitute for Nuclear Research and Nuclear Energy, BG-1784 Sofia, BulgariaK. MallotDeutsches Elektronen-Synchrotron (DESY), D-15738 Zeuthen, GermanyG. ManevaInstitute for Nuclear Research and Nuclear Energy, BG-1784 Sofia, BulgariaK. MannheimUniversität Würzburg, D-97074 Würzburg, GermanyL. MaraschiINAF National Institute for Astrophysics, I-00136 Rome, ItalyB. MarcoteUniversitat de Barcelona, ICC, IEEC-UB, E-08028 Barcelona, SpainM. MariottiUniversità di Padova and INFN, I-35131 Padova, ItalyM. MartínezIFAE, Campus UAB, E-08193 Bellaterra, SpainD. MazinMax-Planck-Institut für Physik, D-80805 München, GermanyU. MenzelMax-Planck-Institut für Physik, D-80805 München, GermanyJ. M. MirandaUniversità di Siena, and INFN Pisa, I-53100 Siena, ItalyR. MirzoyanMax-Planck-Institut für Physik, D-80805 München, GermanyA. MoralejoIFAE, Campus UAB, E-08193 Bellaterra, SpainP. Munar-AdroverUniversitat de Barcelona, ICC, IEEC-UB, E-08028 Barcelona, SpainD. NakajimaJapanese MAGIC Consortium, Division of Physics and Astronomy, Kyoto University, JapanV. NeustroevFinnish MAGIC Consortium, Tuorla Observatory, University of Turku and Department of Physics, University of Oulu, FinlandA. NiedźwieckiUniversity of Łódź, PL-90236 Lodz, PolandK. NilssonFinnish MAGIC Consortium, Tuorla Observatory, University of Turku and Department of Physics, University of Oulu, FinlandK. NishijimaJapanese MAGIC Consortium, Division of Physics and Astronomy, Kyoto University, JapanK. NodaMax-Planck-Institut für Physik, D-80805 München, GermanyR. OritoJapanese MAGIC Consortium, Division of Physics and Astronomy, Kyoto University, JapanA. OverkempingTechnische Universität Dortmund, D-44221 Dortmund, GermanyS. PaianoUniversità di Padova and INFN, I-35131 Padova, Italy
2015en
ABI
Аннотация
PG 1553+113 is a very-high-energy (VHE, E>100 GeV) gamma-ray emitter classified as a BL Lac object. Its redshift is constrained by intergalactic absorption lines in the range 0.4<z<0.58. The MAGIC telescopes have monitored the source's activity since 2005. In early 2012, PG 1553+113 was found in a high-state, and later, in April of the same year, the source reached the highest VHE flux state detected so far. Simultaneous observations carried out in X-rays during 2012 April show similar flaring behaviour. In contrast, the gamma-ray flux at E<100 GeV observed by Fermi-LAT is compatible with steady emission. In this paper, a detailed study of the flaring state is presented. The VHE spectrum shows clear curvature, being well fitted either by a power-law with an exponential cut-off or by a log-parabola. A simple power-law fit hypothesis for the observed shape of the PG 1553+113 VHE gamma-ray spectrum is rejected with a high significance (fit probability P=2.6 x 10^{-6}). For the first time a VHE spectral shape compatible with an exponential decay has been found in a distant blazar (z>0.2). The observed curvature is compatible with the extragalactic background light (EBL) imprint predicted by the current generation of EBL models assuming a redshift z~0.4. New constraints on the redshift were derived from the VHE spectrum. These constraints are compatible with previous limits and suggest that the source is most likely located around the optical lower limit, z=0.4. Finally, we find that the synchrotron self-Compton (SSC) model gives a satisfactory description of the observed multi-wavelength spectral energy distribution during the flare.
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