Long-term multi-wavelength study of 1ES 0647+250

¹ Instituto de Astrofísica de Canarias and Dpto. de Astrofísica, Universidad de La Laguna, 38200 La Laguna, Tenerife, Spain
² National Institute for Astrophysics (INAF), 00136 Rome, Italy
³ Università di Udine and INFN Trieste, 33100 Udine, Italy
⁴ Max-Planck-Institut für Physik, 80805 München, Germany
⁵ Università di Padova and INFN, 35131 Padova, Italy
⁶ Institut de Física d’Altes Energies (IFAE), The Barcelona Institute of Science and Technology (BIST), 08193 Bellaterra, Barcelona, Spain
⁷ Japanese MAGIC Group: Institute for Cosmic Ray Research (ICRR), The University of Tokyo, Kashiwa, 277-8582 Chiba, Japan
⁸ Technische Universität Dortmund, 44221 Dortmund, Germany
⁹ Croatian MAGIC Group: University of Zagreb, Faculty of Electrical Engineering and Computing (FER), 10000 Zagreb, Croatia
¹⁰ IPARCOS Institute and EMFTEL Department, Universidad Complutense de Madrid, 28040 Madrid, Spain
¹¹ Centro Brasileiro de Pesquisas Físicas (CBPF), 22290-180 URCA Rio de Janeiro, RJ, Brazil
¹² University of Lodz, Faculty of Physics and Applied Informatics, Department of Astrophysics, 90-236 Lodz, Poland
¹³ Instituto de Astrofísica de Andalucía-CSIC, Glorieta de la Astronomía s/n, 18008 Granada, Spain
¹⁴ Deutsches Elektronen-Synchrotron (DESY), 15738 Zeuthen, Germany
¹⁵ ETH Zürich, 8093 Zürich, Switzerland
¹⁶ Università di Pisa and INFN Pisa, 56126 Pisa, Italy
¹⁷ Universitat de Barcelona, ICCUB, IEEC-UB, 08028 Barcelona, Spain
¹⁸ Armenian MAGIC Group: A. Alikhanyan National Science Laboratory, 0036 Yerevan, Armenia
¹⁹ Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas, 28040 Madrid, Spain
²⁰ Department for Physics and Technology, University of Bergen, 5007 Bergen, Norway
²¹ INFN MAGIC Group: INFN Sezione di Catania and Dipartimento di Fisica e Astronomia, University of Catania, 95123 Catania, Italy
²² INFN MAGIC Group: INFN Sezione di Torino and Università degli Studi di Torino, 10125 Torino, Italy
²³ INFN MAGIC Group: INFN Sezione di Bari and Dipartimento Interateneo di Fisica dell’Università e del Politecnico di Bari, 70125 Bari, Italy
²⁴ Croatian MAGIC Group: University of Rijeka, Department of Physics, 51000 Rijeka, Croatia
²⁵ Universität Würzburg, 97074 Würzburg, Germany
²⁶ University of Geneva, Chemin d’Ecogia 16, 1290 Versoix, Switzerland
²⁷ Finnish MAGIC Group: Finnish Centre for Astronomy with ESO, University of Turku, 20014 Turku, Finland
²⁸ Departament de Física, and CERES-IEEC, Universitat Autònoma de Barcelona, 08193 Bellaterra, Spain
²⁹ Japanese MAGIC Group: Physics Program, Graduate School of Advanced Science and Engineering, Hiroshima University, 739-8526 Hiroshima, Japan
³⁰ Armenian MAGIC Group: ICRANet-Armenia at NAS RA, 0019 Yerevan, Armenia
³¹ Croatian MAGIC Group: University of Split, Faculty of Electrical Engineering, Mechanical Engineering and Naval Architecture (FESB), 21000 Split, Croatia
³² Croatian MAGIC Group: Josip Juraj Strossmayer University of Osijek, Department of Physics, 31000 Osijek, Croatia
³³ Japanese MAGIC Group: Department of Physics, Kyoto University, 606-8502 Kyoto, Japan
³⁴ Japanese MAGIC Group: Department of Physics, Tokai University, Hiratsuka, 259-1292 Kanagawa, Japan
³⁵ Università di Siena and INFN Pisa, 53100 Siena, Italy
³⁶ Saha Institute of Nuclear Physics, A CI of Homi Bhabha National Institute, Kolkata, 700064 West Bengal, India
³⁷ Inst. for Nucl. Research and Nucl. Energy, Bulgarian Academy of Sciences, 1784 Sofia, Bulgaria
³⁸ Japanese MAGIC Group: Department of Physics, Yamagata University, Yamagata 990-8560, Japan
³⁹ Finnish MAGIC Group: Space Physics and Astronomy Research Unit, University of Oulu, 90014 Oulu, Finland
⁴⁰ Croatian MAGIC Group: Ruđer Bošković Institute, 10000 Zagreb, Croatia
⁴¹ Japanese MAGIC Group: Institute for Space-Earth Environmental Research and Kobayashi-Maskawa Institute for the Origin of Particles and the Universe, Nagoya University, 464-6801 Nagoya, Japan
⁴² INFN MAGIC Group: INFN Sezione di Perugia, 06123 Perugia, Italy
⁴³ INFN MAGIC Group: INFN Roma Tor Vergata, 00133 Roma, Italy
⁴⁴ Japanese MAGIC Group: Department of Physics, Konan University, Kobe, Hyogo 658-8501, Japan
⁴⁵ International Center for Relativistic Astrophysics (ICRA), Rome, Italy
⁴⁶ University of Innsbruck, Institute for Astro and Particle Physics, Innsbruck, Austria
⁴⁷ Port d’Informació Científica (PIC), 08193 Bellaterra, Barcelona, Spain
⁴⁸ Ruhr-Universität Bochum, Fakultät für Physik und Astronomie, Astronomisches Institut (AIRUB), 44801 Bochum, Germany
⁴⁹ University of Innsbruck, Institute for Astro- and Particle Physics, Innsbruck, Austria
⁵⁰ Dipartimento di Fisica, Università di Trieste, 34127 Trieste, Italy
⁵¹ University of Lodz, Faculty of Physics and Applied Informatics, Department of Astrophysics, 90-236 Lodz, Poland
⁵² Max-Planck-Institut für Physik, 80805 München, Germany
⁵³ INAF Trieste and Dept. of Physics and Astronomy, University of Bologna, Bologna, Italy
⁵⁴ Japanese MAGIC Group: Institute for Cosmic Ray Research (ICRR), The University of Tokyo, Kashiwa, 277-8582 Chiba, Japan
⁵⁵ INAF-Istituto di Radioastronomia, Via Gobetti 101, 40129 Bologna, Italy
⁵⁶ Finnish Centre for Astronomy with ESO (FINCA), University of Turku, 20014 Turku, Finland
⁵⁷ Aalto University Metsähovi Radio Observatory, Metsähovintie 114, 02540 Kylmälä, Finland
⁵⁸ Institute of Astrophysics, Foundation for Research and Technology-Hellas, 71110 Heraklion, Greece
⁵⁹ Department of Physics, Univ. of Crete, 70013 Heraklion, Greece
⁶⁰ Space Science Data Center (SSDC) – ASI, Via del Politecnico, s.n.c., 00133 Roma, Italy
⁶¹ Italian Space Agency, ASI, Via del Politecnico s.n.c., 00133 Roma, Italy
⁶² Departamento de Astronomía, Universidad de Chile, Camino El Observatorio 1515, Las Condes, Santiago, Chile
⁶³ Istituto di Astrofisica e Planetologia Spaziali-INAF, Via Fosso del Cavaliere 100, 00133 Rome, Italy
⁶⁴ INAF – Osservatorio Astronomico di Roma, Via di Frascati 33, 00040 Monteporzio, Italy
⁶⁵ Owens Valley Radio Observatory, California Institute of Technology, Pasadena, CA 91125, USA
⁶⁶ CePIA, Departamento de Astronomía, Universidad de Concepción, Concepción, Chile

Received: 12 July 2022
Accepted: 18 November 2022

Abstract

Context. The BL Lac object 1ES 0647+250 is one of the few distant γ-ray emitting blazars detected at very high energies (VHEs; ≳100 GeV) during a non-flaring state. It was detected with the MAGIC telescopes during a period of low activity in the years 2009−2011 as well as during three flaring activities in the years 2014, 2019, and 2020, with the highest VHE flux in the last epoch. An extensive multi-instrument data set was collected as part of several coordinated observing campaigns over these years.

Aims. We aim to characterise the long-term multi-band flux variability of 1ES 0647+250, as well as its broadband spectral energy distribution (SED) during four distinct activity states selected in four different epochs, in order to constrain the physical parameters of the blazar emission region under certain assumptions.

Methods. We evaluated the variability and correlation of the emission in the different energy bands with the fractional variability and the Z-transformed discrete correlation function, as well as its spectral evolution in X-rays and γ rays. Owing to the controversy in the redshift measurements of 1ES 0647+250 reported in the literature, we also estimated its distance in an indirect manner through a comparison of the GeV and TeV spectra from simultaneous observations with Fermi-LAT and MAGIC during the strongest flaring activity detected to date. Moreover, we interpret the SEDs from the four distinct activity states within the framework of one-component and two-component leptonic models, proposing specific scenarios that are able to reproduce the available multi-instrument data.

Results. We find significant long-term variability, especially in X-rays and VHE γ rays. Furthermore, significant (3−4σ) correlations were found between the radio, optical, and high-energy (HE) γ-ray fluxes, with the radio emission delayed by about ∼400 days with respect to the optical and γ-ray bands. The spectral analysis reveals a harder-when-brighter trend during the non-flaring state in the X-ray domain. However, no clear patterns were observed for either the enhanced states or the HE (30 MeV < E < 100 GeV) and VHE γ-ray emission of the source. The indirect estimation of the redshift yielded a value of z = 0.45 ± 0.05, which is compatible with some of the values reported in the literature. The SEDs related to the low-activity state and the three flaring states of 1ES 0647+250 can be described reasonably well with the both one-component and two-component leptonic scenarios. However, the long-term correlations indicate the need for an additional radio-producing region located about 3.6 pc downstream from the gamma-ray producing region.