Issue |
A&A
Volume 695, March 2025
|
|
---|---|---|
Article Number | A217 | |
Number of page(s) | 18 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361/202452785 | |
Published online | 21 March 2025 |
Insights from the first flaring activity of a high synchrotron peaked blazar with X-ray polarization and VHE gamma rays
1
Japanese MAGIC Group: Department of Physics, Tokai University, Hiratsuka, 259-1292 Kanagawa, Japan
2
Japanese MAGIC Group: Institute for Cosmic Ray Research (ICRR), The University of Tokyo, Kashiwa, 277-8582 Chiba, Japan
3
ETH Zürich, CH-8093 Zürich, Switzerland
4
Università di Siena and INFN Pisa, I-53100 Siena, Italy
5
Institut de Física d’Altes Energies (IFAE), The Barcelona Institute of Science and Technology (BIST), E-08193 Bellaterra (Barcelona), Spain
6
Universitat de Barcelona, ICCUB, IEEC-UB, E-08028 Barcelona, Spain
7
Instituto de Astrofísica de Andalucía-CSIC, Glorieta de la Astronomía s/n, 18008 Granada, Spain
8
National Institute for Astrophysics (INAF), I-00136 Rome, Italy
9
Università di Udine and INFN Trieste, I-33100 Udine, Italy
10
Max-Planck-Institut für Physik, D-85748 Garching, Germany
11
Università di Padova and INFN, I-35131 Padova, Italy
12
Croatian MAGIC Group: University of Zagreb, Faculty of Electrical Engineering and Computing (FER), 10000 Zagreb, Croatia
13
Centro Brasileiro de Pesquisas Físicas (CBPF), 22290-180 URCA, Rio de Janeiro (RJ), Brazil
14
IPARCOS Institute and EMFTEL Department, Universidad Complutense de Madrid, E-28040 Madrid, Spain
15
Instituto de Astrofísica de Canarias and Dpto. de Astrofísica, Universidad de La Laguna, E-38200 La Laguna, Tenerife, Spain
16
University of Lodz, Faculty of Physics and Applied Informatics, Department of Astrophysics, 90-236 Lodz, Poland
17
Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas, E-28040 Madrid, Spain
18
Departament de Física, and CERES-IEEC, Universitat Autònoma de Barcelona, E-08193 Bellaterra, Spain
19
Università di Pisa and INFN Pisa, I-56126 Pisa, Italy
20
INFN MAGIC Group: INFN Sezione di Bari and Dipartimento Interateneo di Fisica dell’Università e del Politecnico di Bari, I-70125 Bari, Italy
21
Armenian MAGIC Group: A. Alikhanyan National Science Laboratory, 0036 Yerevan, Armenia
22
Department for Physics and Technology, University of Bergen, Bergen, Norway
23
INFN MAGIC Group: INFN Sezione di Torino and Università degli Studi di Torino, I-10125 Torino, Italy
24
Croatian MAGIC Group: University of Rijeka, Faculty of Physics, 51000 Rijeka, Croatia
25
Universität Würzburg, D-97074 Würzburg, Germany
26
Technische Universität Dortmund, D-44221 Dortmund, Germany
27
Japanese MAGIC Group: Physics Program, Graduate School of Advanced Science and Engineering, Hiroshima University, 739-8526 Hiroshima, Japan
28
Deutsches Elektronen-Synchrotron (DESY), D-15738 Zeuthen, Germany
29
Armenian MAGIC Group: ICRANet-Armenia, 0019 Yerevan, Armenia
30
Croatian MAGIC Group: University of Split, Faculty of Electrical Engineering, Mechanical Engineering and Naval Architecture (FESB), 21000 Split, Croatia
31
Croatian MAGIC Group: Josip Juraj Strossmayer University of Osijek, Department of Physics, 31000 Osijek, Croatia
32
Finnish MAGIC Group: Finnish Centre for Astronomy with ESO, Department of Physics and Astronomy, University of Turku, FI-20014 Turku, Finland
33
University of Geneva, Chemin d’Ecogia 16, CH-1290 Versoix, Switzerland
34
Saha Institute of Nuclear Physics, A CI of Homi Bhabha National Institute, Kolkata, 700064 West Bengal, India
35
Inst. for Nucl. Research and Nucl. Energy, Bulgarian Academy of Sciences, BG-1784 Sofia, Bulgaria
36
Japanese MAGIC Group: Department of Physics, Yamagata University, Yamagata 990-8560, Japan
37
Finnish MAGIC Group: Space Physics and Astronomy Research Unit, University of Oulu, FI-90014 Oulu, Finland
38
Japanese MAGIC Group: Chiba University, ICEHAP, 263-8522 Chiba, Japan
39
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
40
Japanese MAGIC Group: Department of Physics, Kyoto University, 606-8502 Kyoto, Japan
41
INFN MAGIC Group: INFN Roma Tor Vergata, I-00133 Roma, Italy
42
Japanese MAGIC Group: Department of Physics, Konan University, Kobe, Hyogo 658-8501, Japan
43
also at International Center for Relativistic Astrophysics (ICRA), Rome, Italy
44
also at Port d’Informació Científica (PIC), E-08193 Bellaterra (Barcelona), Spain
45
also at Department of Physics, University of Oslo, Oslo, Norway
46
also at Dipartimento di Fisica, Università di Trieste, I-34127 Trieste, Italy
47
Max-Planck-Institut für Physik, D-85748 Garching, Germany
48
also at INAF Padova, Padova, Italy
49
Japanese MAGIC Group: Institute for Cosmic Ray Research (ICRR), The University of Tokyo, Kashiwa, 277-8582 Chiba, Japan
50
NASA Marshall Space Flight Center, Huntsville, AL 35812, USA
51
Institute of Astrophysics, Foundation for Research and Technology – Hellas, GR-70013 Heraklion, Crete, Greece
52
INAF Istituto di Astrofisica e Planetologia Spaziali, Via del Fosso del Cavaliere 100, 00133 Roma, Italy
53
ASI – Agenzia Spaziale Italiana, Via del Politecnico snc, 00133 Roma, Italy
54
Dipartimento di Fisica, Università degli Studi di Roma “La Sapienza”, Piazzale Aldo Moro 5, 00185 Roma, Italy
55
Dipartimento di Fisica, Università degli Studi di Roma “Tor Vergata”, Via della Ricerca Scientifica 1, 00133 Roma, Italy
56
Science & Technology Institute, Universities Space Research Association, 320 Sparkman Drive, Huntsville, AL 35805, USA
57
Quasar Science Resource S.L. for the European Space Agency (ESA), European Space Astronomy Centre (ESAC), Camino Bajo del Castillo s/n, 28692 Villanueva de la Cañada, Madrid, Spain
58
Space Science Data Center, Agenzia Spaziale Italiana, Via del Politecnico snc, 00133 Roma, Italy
59
INAF Osservatorio Astronomico di Roma, Via Frascati 33, 00078 Monte Porzio Catone (RM), Italy
60
Hans-Haffner-Sternwarte, Hettstadt; Naturwissenschaftliches Labor für Schüler am FKG; Friedrich-Koenig-Gymnasium, D-97082 Würzburg, Germany
61
Astrophysics Research Institute, Liverpool John Moores University, Liverpool Science Park IC2, 146 Brownlow Hill, Liverpool, UK
62
Institute for Astrophysical Research, Boston University, 725 Commonwealth Avenue, Boston, MA 02215, USA
63
Perkins Telescope Observatory, Boston University, 725 Commonwealth Avenue, Boston, MA 02215, USA
64
Institute of Integrated Research, Institute of Science Tokyo, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8550, Japan
65
Department of Physics, Graduate School of Advanced Science and Engineering, Hiroshima University Kagamiyama, 1-3-1 Higashi-Hiroshima, Hiroshima 739-8526, Japan
66
Hiroshima Astrophysical Science Center, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8526, Japan
67
Core Research for Energetic Universe (Core-U), Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8526, Japan
68
Astronomy Research Center, Chiba Institute of Technology, 2-17-1 Tsudanuma, Narashino, Chiba 275-0016, Japan
69
Institut de Radioastronomie Millimétrique, Avenida Divina Pastora, 7, Local 20, E–18012 Granada, Spain
70
Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany
71
Center for Astrophysics | Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138, USA
72
Orchideenweg 8, 53123 Bonn, Germany
73
INAF Istituto di Radioastronomia, Via P. Gobetti 101, I-40129 Bologna, Italy
74
now at Université Paris Cité, CNRS, Astroparticule et Cosmologie, F-75013 Paris, France
⋆ Corresponding authors; A. Arbet Engels, L. Heckmann, D. Paneque, E-mail: contact.magic@mpp.mpg.de
Received:
28
October
2024
Accepted:
17
January
2025
Context. Blazars exhibit strong variability across the entire electromagnetic spectrum, including periods of high-flux states commonly known as flares. The physical mechanisms in blazar jets responsible for flares remain poorly understood to date.
Aims. Our aim is to better understand the emission mechanisms during blazar flares using X-ray polarimetry and broadband observations from the archetypical TeV blazar Mrk 421, which can be studied with higher accuracy than other blazars that are dimmer and/or located farther away.
Methods. We studied a flaring activity from December 2023 that was characterized from radio to very high-energy (VHE; E > 0.1 TeV) gamma rays with MAGIC, Fermi-LAT, Swift, XMM-Newton, and several optical and radio telescopes. These observations included, for the first time for a gamma-ray flare of a blazar, simultaneous X-ray polarization measurements with IXPE, in addition to optical and radio polarimetry data. We quantify the variability and correlations among the multi-band flux and polarization measurements, and describe the varying broadband emission within a theoretical scenario constrained by the polarization data.
Results. We find substantial variability in both X-rays and VHE gamma rays throughout the campaign, with the highest VHE flux above 0.2 TeV occurring during the IXPE observing window, and exceeding twice the flux of the Crab Nebula. However, the VHE and X-ray spectra are on average softer, and the correlation between these two bands is weaker than those reported in the previous flares of Mrk 421. IXPE reveals an X-ray polarization degree significantly higher than that at radio and optical frequencies, similar to previous results for Mrk 421 and other high synchrotron peaked blazars. Differently to past observations, the X-ray polarization angle varies by ∼100° on timescales of days, and the polarization degree changes by more than a factor of 4. The highest X-ray polarization degree, analyzed in 12 h time intervals, reaches 26 ± 2%, around which an X-ray counter-clockwise hysteresis loop is measured with XMM-Newton. It suggests that the X-ray emission comes from particles close to the high-energy cutoff, hence possibly probing an extreme case of the Turbulent Extreme Multi-Zone model for which the chromatic trend in the polarization may be more pronounced than theoretically predicted. We model the broadband emission with a simplified stratified jet model throughout the flare. The polarization measurements imply an electron distribution in the X-ray emitting region with a very high minimum Lorentz factor (), which is expected in electron-ion plasma, as well as a variation of the emitting region size of up to a factor of 3 during the flaring activity. We find no correlation between the fluxes and the evolution of the model parameters, which indicates a stochastic nature of the underlying physical mechanism that likely explains the lack of a tight X-ray/VHE correlation during this flaring activity. Such behavior would be expected in a highly turbulent electron-ion plasma crossing a shock front.
Key words: acceleration of particles / radiation mechanisms: non-thermal / galaxies: active / BL Lacertae objects: individual: Markarian 421 / gamma rays: general / X-rays: general
© The Authors 2025
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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Open access funding provided by Max Planck Society.
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