MAGIC and H.E.S.S. detect VHE gamma rays from the blazar OT 081 for the first time: a deep multiwavelength study

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2022-03-18
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en
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Proceedings of Science, Volume 395
Abstract
OT 081 is a luminous blazar well known for its variability in many energy bands. The very-high-energy (VHE; E > 100 GeV) gamma-ray emission from the source was discovered by MAGIC and H.E.S.S. during flaring activity in July 2016, after a trigger from the Large Area Telescope (LAT) onboard the Fermi satellite. By analysing the multiwavelength light curves and the broadband spectral energy distribution (SED), we study the activity of the source and investigate four individual states of activity in the window from MJD 57575 to 57602. The intrinsic gamma-ray spectrum can be described by a power law with spectral indices of 3.27 ± 0.44 (MAGIC) and 3.39 ± 0.58 (H.E.S.S.) over energy ranges 60-300 GeV and 120-500 GeV, respectively. The combined contemporaneous high-energy (HE; E > 100 MeV) through VHE SED shows curvature and can be described by a log-parabola shape. A simple one-zone synchrotron self-Compton (SSC) model is not sufficient to describe the broadband SED. The presence of broad emission lines in the optical spectrum of the source challenges the categorisation of OT 081 as a BL Lac and, together with the emission scenarios tested, points to the possibility that the source is transitional in nature between a BL Lac and a flat-spectrum radio quasar.
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Funding Information: We acknowledge the support from the agencies and organisations listed here: https://magic.mpp.mpg.de/acknowledgments_ICRC2021. The Fermi-LAT Collaboration acknowledges support for LAT development, operation, and data analysis from NASA and DOE (United States), CEA/Irfu and IN2P3/CNRS (France), ASI and INFN (Italy), MEXT, KEK, and JAXA (Japan), and the K.A. Wallenberg Foundation, the Swedish Research Council, and the National Space Board (Sweden). Science analysis support in the operations phase from INAF (Italy) and CNES (France) is also gratefully acknowledged. This work was performed in part under DOE Contract DE-AC02-76SF00515. A.V.F. and W.Z. are grateful for support from NASA grant NNX12AF12G, the Christopher R. Redlich Fund, the TABASGO Foundation, and the U.C. Berkeley Miller Institute for Basic Research in Science (in which A.V.F. is a Senior Fellow). KAIT and its ongoing operation were made possible by donations from Sun Microsystems, Inc., the Hewlett-Packard Company, AutoScopeCorporation, Lick Observatory, the US National Science Foundation, the University of California, the Sylvia and Jim Katzman Foundation, and the TABASGO Foundation. Research at Lick Observatory is partially supported by a generous gift from Google. Funding Information: We acknowledge the support from the agencies and organisations listed here: https://magic. mpp.mpg.de/acknowledgments_ICRC2021. The Fermi-LAT Collaboration acknowledges support for LAT development, operation, and data analysis from NASA and DOE (United States), CEA/Irfu and IN2P3/CNRS (France), ASI and INFN (Italy), MEXT, KEK, and JAXA (Japan), and the K.A. Wallenberg Foundation, the Swedish Research Council, and the National Space Board (Sweden). Science analysis support in the operations phase from INAF (Italy) and CNES (France) is also gratefully acknowledged. This work was performed in part under DOE Contract DE-AC02-76SF00515. A.V.F. and W.Z. are grateful for support from NASA grant NNX12AF12G, the Christopher R. Redlich Fund, the TABASGO Foundation, and the U.C. Berkeley Miller Institute for Basic Research in Science (in which A.V.F. is a Senior Fellow). KAIT and its ongoing operation were made possible by donations from Sun Microsystems, Inc., the Hewlett-Packard Company, AutoScope Corporation, Lick Observatory, the US National Science Foundation, the University of California, the Sylvia and Jim Katzman Foundation, and the TABASGO Foundation. Research at Lick Observatory is partially supported by a generous gift from Google. Publisher Copyright: © Copyright owned by the author(s) under the terms of the Creative Commons.
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Manganaro , M , Cerruti , M , Tavecchio , F , Hovatta , T , Lähteenmäki , A , H.E.S.S. , Fermi Large Area Telescope Collaboration & MAGIC Collaboration 2022 , ' MAGIC and H.E.S.S. detect VHE gamma rays from the blazar OT 081 for the first time: a deep multiwavelength study ' , Proceedings of Science , vol. 395 , 815 . < https://pos.sissa.it/395/815/ >