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Published March 2021 | Accepted Version + Published
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VHE gamma-ray detection of FSRQ QSO B1420+326 and modeling of its enhanced broadband state in 2020

Acciari, V. A. ORCID icon
Ansoldi, S. ORCID icon
Antonelli, L. A. ORCID icon
Arbet Engels, A. ORCID icon
Artero, M.
Asano, K.
Baack, D. ORCID icon
Babić, A. ORCID icon
Baquero, A.
Barres de Almeida, U. ORCID icon
Barrio, J. A. ORCID icon
Becerra González, J. ORCID icon
Bednarek, W. ORCID icon
Bellizzi, L.
Bernardini, E. ORCID icon
Bernardos, M.
Berti, A. ORCID icon
Besenrieder, J.
Bhattacharyya, W. ORCID icon
Bigongiari, C. ORCID icon
Biland, A. ORCID icon
Blanch, O. ORCID icon
Bonnoli, G. ORCID icon
Bošnjak, Ž. ORCID icon
Busetto, G. ORCID icon
Carosi, R. ORCID icon
Ceribella, G.
Cerruti, M. ORCID icon
Chai, Y. ORCID icon
Chilingarian, A. ORCID icon
Cikota, S. ORCID icon
Colak, S. M. ORCID icon
Colombo, E. ORCID icon
Contreras, J. L. ORCID icon
Cortina, J. ORCID icon
Covino, S. ORCID icon
D'Amico, G.
D'Elia, V.
Da Vela, P.
Dazzi, F. ORCID icon
De Angelis, A. ORCID icon
De Lotto, B. ORCID icon
Delfino, M. ORCID icon
Delgado, J. ORCID icon
Delgado Mendez, C.
Depaoli, D. ORCID icon
Di Pierro, F. ORCID icon
Di Venere, L. ORCID icon
Do Souto Espiñeira, E. ORCID icon
Dominis Prester, D. ORCID icon
Donini, A. ORCID icon
Dorner, D. ORCID icon
Doro, M. ORCID icon
Elsaesser, D. ORCID icon
Fallah Ramazani, V. ORCID icon
Fattorini, A.
Ferrara, G. ORCID icon
Foffano, L. ORCID icon
Fonseca, M. V. ORCID icon
Font, L. ORCID icon
Fruck, C. ORCID icon
Fukami, S.
García López, R. J. ORCID icon
Garczarczyk, M. ORCID icon
Gasparyan, S.
Gaug, M. ORCID icon
Giglietto, N. ORCID icon
Giordano, F. ORCID icon
Gliwny, P. ORCID icon
Godinović, N. ORCID icon
Green, J. G.
Green, D. ORCID icon
Hadasch, D. ORCID icon
Hahn, A. ORCID icon
Heckmann, L.
Herrera, J. ORCID icon
Hoang, J. ORCID icon
Hrupec, D. ORCID icon
Hütten, M. ORCID icon
Inada, T.
Inoue, S. ORCID icon
Ishio, K.
Iwamura, Y.
Jormanainen, J.
Jouvin, L. ORCID icon
Kajiwara, Y.
Karjalainen, M.
Kerszberg, D. ORCID icon
Kobayashi, Y.
Kubo, H. ORCID icon
Kushida, J. ORCID icon
Lamastra, A. ORCID icon
Lelas, D. ORCID icon
Leone, F. ORCID icon
Lindfors, E. ORCID icon
Lombardi, S. ORCID icon
Longo, F. ORCID icon
López-Coto, R. ORCID icon
López-Moya, M.
López-Oramas, A. ORCID icon
Loporchio, S. ORCID icon
Machado de Oliveira Fraga, B. ORCID icon
Maggio, C. ORCID icon
Majumdar, P. ORCID icon
Makariev, M. ORCID icon
Mallamaci, M. ORCID icon
Maneva, G. ORCID icon
Manganaro, M. ORCID icon
Mannheim, K. ORCID icon
Maraschi, L.
Mariotti, M. ORCID icon
Martínez, M. ORCID icon
Mazin, D. ORCID icon
Mender, S. ORCID icon
Mićanović, S. ORCID icon
Miceli, D. ORCID icon
Miener, T.
Minev, M.
Miranda, J. M. ORCID icon
Mirzoyan, R. ORCID icon
Molina, E. ORCID icon
Moralejo, A. ORCID icon
Morcuende, D. ORCID icon
Moreno, V. ORCID icon
Moretti, E. ORCID icon
Neustroev, V. ORCID icon
Nigro, C. ORCID icon
Nilsson, K. ORCID icon
Ninci, D. ORCID icon
Nishijima, K. ORCID icon
Noda, K. ORCID icon
Nozaki, S. ORCID icon
Ohtani, Y.
Oka, T. ORCID icon
Otero-Santos, J. ORCID icon
Paiano, S.
Palatiello, M. ORCID icon
Paneque, D. ORCID icon
Paoletti, R. ORCID icon
Paredes, J. M. ORCID icon
Pavletić, L. ORCID icon
Peñil, P.
Perennes, C.
Persic, M. ORCID icon
Prada Moroni, P. G. ORCID icon
Prandini, E. ORCID icon
Priyadarshi, C.
Puljak, I. ORCID icon
Rhode, W. ORCID icon
Ribó, M. ORCID icon
Rico, J. ORCID icon
Righi, C. ORCID icon
Rugliancich, A. ORCID icon
Saha, L. ORCID icon
Sahakyan, N. ORCID icon
Saito, T.
Sakurai, S.
Satalecka, K. ORCID icon
Saturni, F. G.
Schleicher, B.
Schmidt, K. ORCID icon
Schweizer, T. ORCID icon
Sitarek, J. ORCID icon
Šnidarić, I.
Sobczynska, D. ORCID icon
Spolon, A. ORCID icon
Stamerra, A. ORCID icon
Strom, D. ORCID icon
Strzys, M.
Suda, Y. ORCID icon
Surić, T.
Takahashi, M. ORCID icon
Tavecchio, F. ORCID icon
Temnikov, P. ORCID icon
Terzić, T. ORCID icon
Teshima, M.
Torres-Albà, N. ORCID icon
Tosti, L.
Truzzi, S.
Tutone, A.
van Scherpenberg, J. ORCID icon
Vanzo, G. ORCID icon
Vazquez Acosta, M. ORCID icon
Ventura, S. ORCID icon
Verguilov, V. ORCID icon
Vigorito, C. F. ORCID icon
Vitale, V. ORCID icon
Vovk, I. ORCID icon
Will, M. ORCID icon
Zarić, D. ORCID icon
Angioni, R. ORCID icon
D'Ammando, F.
Ciprini, S.
Cheung, C. C.
Orienti, M.
Pacciani, L.
Prajapati, P.
Kumar, P.
Ganesh, S.
Minev, M.
Kurtenkov, A.
Marchini, A. ORCID icon
Carrasco, L.
Escobedo, G.
Porras, A.
Recillas, E.
Lähteenmäki, A. ORCID icon
Tornikoski, M. ORCID icon
Berton, M. ORCID icon
Tammi, J.
Vera, R. J. C.
Jorstad, S. G. ORCID icon
Marscher, A. P. ORCID icon
Weaver, Z. R. ORCID icon
Hart, M.
Hallum, M. K.
Larionov, V. M. ORCID icon
Borman, G. A.
Grishina, T. S.
Kopatskaya, E. N.
Larionova, E. G.
Nikiforova, A. A.
Morozova, D. A.
Savchenko, S. S.
Troitskaya, Yu. V.
Troitsky, I. S.
Vasilyev, A. A.
Hodges, M.
Hovatta, T. ORCID icon
Kiehlmann, S. ORCID icon
Max-Moerbeck, W. ORCID icon
Readhead, A. C. S. ORCID icon
Reeves, R. ORCID icon
Pearson, T. J. ORCID icon
MAGIC Collaboration


Context. QSO B1420+326 is a blazar classified as a flat-spectrum radio quasar (FSRQ). At the beginning of the year 2020, it was found to be in an enhanced flux state and an extensive multiwavelength campaign allowed us to trace the evolution of the flare. Aims. We search for very high-energy (VHE) gamma-ray emission from QSO B1420+326 during this flaring state. We aim to characterize and model the broadband emission of the source over different phases of the flare. Methods. The source was observed with a number of instruments in radio, near-infrared, optical (including polarimetry and spectroscopy), ultraviolet, X-ray, and gamma-ray bands. We use dedicated optical spectroscopy results to estimate the accretion disk and the dust torus luminosity. We performed spectral energy distribution modeling in the framework of combined synchrotron-self-Compton and external Compton scenario in which the electron energy distribution is partially determined from acceleration and cooling processes. Results. During the enhanced state, the flux of both SED components of QSO B1420+326 drastically increased and the peaks were shifted to higher energies. Follow-up observations with the MAGIC telescopes led to the detection of VHE gamma-ray emission from this source, making it one of only a handful of FSRQs known in this energy range. Modeling allows us to constrain the evolution of the magnetic field and electron energy distribution in the emission region. The gamma-ray flare was accompanied by a rotation of the optical polarization vector during a low -polarization state. Also, a new superluminal radio knot contemporaneously appeared in the radio image of the jet. The optical spectroscopy shows a prominent FeII bump with flux evolving together with the continuum emission and a MgII line with varying equivalent width.

Additional Information

© 2021 ESO. Received: 15 October 2020; Accepted: 18 December 2020; Published online 29 March 2021. We would like to dedicate this paper to the memory of our friend and colleague, Dr. Valeri Larionov (1950−2020), who enthusiastically contributed to this and many other projects aimed at understanding blazars. We would like to thank the Instituto de Astrofísica de Canarias for the excellent working conditions at the Observatorio del Roque de los Muchachos in La Palma. The financial support of the German BMBF and MPG; the Italian INFN and INAF; the Swiss National Fund SNF; the ERDF under the Spanish MINECO (FPA2017-87859-P, FPA2017-85668-P, FPA2017-82729-C6-2-R, FPA2017-82729-C6-6-R, FPA2017-82729-C6-5-R, AYA2015-71042-P, AYA2016-76012-C3-1-P, ESP2017-87055-C2-2-P, FPA2017-90566-REDC); the Indian Department of Atomic Energy; the Japanese ICRR, the University of Tokyo, JSPS, and MEXT; the Bulgarian Ministry of Education and Science, National RI Roadmap Project DO1-268/16.12.2019 and the Academy of Finland grant nr. 320045 is gratefully acknowledged. This work was also supported by the Spanish Centro de Excelencia "Severo Ochoa" SEV-2016-0588 and SEV-2015-0548, the Unidad de Excelencia "María de Maeztu" MDM-2014-0369 and the "la Caixa" Foundation (fellowship LCF/BQ/PI18/11630012), by the Croatian Science Foundation (HrZZ) Project IP-2016-06-9782 and the University of Rijeka Project, by the DFG Collaborative Research Centers SFB823/C4 and SFB876/C3, the Polish National Research Centre grant UMO-2016/22/M/ST9/00382 and by the Brazilian MCTIC, CNPq and FAPERJ. The Fermi-LAT Collaboration acknowledges generous ongoing support from a number of agencies and institutes that have supported both the development and the operation of the LAT, as well as scientific data analysis. These include the National Aeronautics and Space Administration and the Department of Energy in the United States; the Commissariat à l'Energie Atomique and the Centre National de la Recherche Scientifique/Institut National de Physique Nucléaire et de Physique des Particules in France; the Agenzia Spaziale Italiana and the Istituto Nazionale di Fisica Nucleare in Italy; the Ministry of Education, Culture, Sports, Science and Technology (MEXT), High Energy Accelerator Research Organization (KEK), and Japan Aerospace Exploration Agency (JAXA) in Japan; and the K. A. Wallenberg Foundation, the Swedish Research Council, and the Swedish National Space Board in Sweden. Additional support for science analysis during the operations phase is gratefully acknowledged from the Istituto Nazionale di Astrofisica in Italy and the Centre National d'Etudes Spatiales in France. This work was performed in part under DOE Contract DE-AC02-76SF00515. This publication makes use of data obtained at the Metsähovi Radio Observatory, operated by Aalto University in Finland. This research has made use of data from the OVRO 40 m monitoring program Richards et al. (2011) which is supported in part by NASA grants NNX08AW31G, NNX11A043G, and NNX14AQ89G and NSF grants AST-0808050 and AST-1109911. This study was based in part on observations conducted using the 1.8 m Perkins Telescope Observatory (PTO) in Arizona, which is owned and operated by Boston University. The research at Boston University was supported in part by NASA Fermi GI program grants 80NSSC17K0649, 80NSSC19K1504, and 80NSSC19K1505. We thank the ASAS-SN team for making their data publicly available. The VLBA is an instrument of the National Radio Astronomy Observatory. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated by Associated Universities, Inc. This work made use of the Lowell Discovery Telescope (formerly Discovery Channel Telescope) at Lowell Observatory. Lowell is a private, nonprofit institution dedicated to astrophysical research and public appreciation of astronomy and operates the LDT in partnership with Boston University, the University of Maryland, the University of Toledo, Northern Arizona University, and Yale University. We acknowledge support by Bulgarian National Science Fund under grant DN18-10/2017 and National RI Roadmap Projects DO1-277/16.12.2019 and DO1-268/16.12.2019 of the Ministry of Education and Science of the Republic of Bulgaria.

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August 20, 2023
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