Insights from the first flaring activity of a high synchrotron peaked blazar with X-ray polarization and VHE gamma rays

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 ($ \gamma\prime_{\mathrm{min}}\gtrsim10^4 $), 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.

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Journal
Astronomy and Astrophysics
Published
2025-02-21
DOI
https://doi.org/10.1051/0004-6361/202452785
Citations
3
Primary Topic
Astrophysics and Cosmic Phenomena
Type
article
Field-Weighted Citation Impact
5.61

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article

Insights from the first flaring activity of a high synchrotron peaked blazar with X-ray polarization and VHE gamma rays

A. Hahn, M. Martínez, J. Sitarek, K. Nishijima et al.
3 citations
Astronomy and Astrophysics
Astrophysics and Cosmic Phenomena
5.61
article

Insights from the first flaring activity of a high synchrotron peaked blazar with X-ray polarization and VHE gamma rays

A. Hahn, M. Martínez, J. Sitarek, K. Nishijima, I. de la Calle Pérez, D. Sobczyńska, O. Blanch, R. Walter, S. Kiehlmann, Irene Burelli, Hiroshi Akitaya, M. Persic, Marine Pihet, Jürgen Besenrieder, T. Njoh Ekoume, S. Mender, Laura Di Gesu, E. Molina, D. Israyelyan, Francesco Gabriele Saturni, Alvaro Mas-Aguilar, C. Bigongiari, P. Günther, Juliane van Scherpenberg, Dawoon E. Kim, S. Abe, P. Temnikov, H. Tajima, J.L Schubert, M. Mariotti, M. Takahashi, C. Delgado Mendez, Jarred Gershon Green, L. Font, Daniel Morcuende, M. Delfino, J. Abhir, Laura Eisenberger, F. Di Pierro, A. Sota, A. Kraus, Ioannis Liodakis, R. Takeishi, R. Steineke, J. Baxter, U. Barres de Almeida, Pouya M. Kouch, E. Bernardini, Garrett K. Keating, A. López-Oramas, E. Angelakis, F. Podobnik, A. Biland, D. Reinhart, R. Paoletti, D. Cerasole, R. Grau, J. A. Barrio, Stefan Fröse, G. Principe, Svetlana G. Jorstad, W. Peter Maksym, M. Lynne Saade, I. Batković, G. Maneva, H. Jermak, M. Feige, D. Dorner, G. D'Amico, P. Maruševec, Jorge Otero-Santos, Jelena Strišković, M. Perri, M. Carretero-Castrillo, Hiroaki Kubo, Takeshi Nakamori, E. Prandini, M. Ribó, C. Vigorito, V. Fallah Ramazanı, I. Myserlis, S. Paiano, T. Kayanoki, E. Colombo, N. Sahakyan, Y. Fukazawa, B. De Lotto, Sofia Ventura, J. M. Paredes, I. Agudo, T. Terzić, Ramprasad Rao, Antonio Tutone, V. A. Acciari, G. Verna, Takashi Itokawa, J. Delgado, Davide Miceli, Steven R. Ehlert, C.T. Chen, M. Nievas Rosillo, K. Noda, Martin Will, V. Neustroev, C. McCall, F. J. Aceituno, N. Godinović, Makoto Uemura, Lea Heckmann, Vitalii Sliusar, C. Nanci, Santiago Ubach, L. Fariña, M. Doro, A. Berti, A. Babić, G. Bonnoli, L. Foffano, A. Stamerra, H. A. Mondal, T. Mizuno, V. Casanova, D. Mazin, K. Terauchi, N. Giglietto, D. Dominis Prester, A. Chilingarian, S. Lombardi, Raniere de Menezes, M. Gaug, Janusz Konrad, Cornelia Arcaro, Gabriella Silvestri, J. Cortina, T. Hassan, Felix Schmuckermaier, W. Rhode, Y. Chai, S. Covino, Arnau Aguasca-Cabot, Ievgen Vovk, G. Ceribella, F. Longo, Katsuaki Asano, M. Garczarczyk, Mahito Sasada, I. A. Steele, Jenni Jormanainen, Gert Werner Kluge, D. Elsäesser, Ryo Imazawa, S. Loporchio, Ilaria Viale, R. Middei, Stephan Dürr, Mark Gurwell, P. Gliwny, G. Pirola, M. Manganaro, J. G. Giesbrecht Paiva, A. Donini, M. Strzys, J. Rico, A. Okumura, Magda Gonzalez, A. Sciaccaluga, A. Cifuentes, P. Kaaret, T. Aniello, David A. Green, Irene Jiménez Martínez, S. Ansoldi, J. M. Miranda, Koji S. Kawabata, A.J. Castro-Tirado, E. Lyard, Alessandro Vigliano, Chiara Righi, C. Nigro, F. Verrecchia, Lukas Nickel, J. Kushida, Stefano Menchiari, Martin Heidemann, M. Peresano, R. Carosi, L. A. Antonelli, K. Mannheim, L. Di Venere, F. D'Ammando, M. Khachatryan, J. Bernete, E. Bronzini, A. Campoy-Ordaz, T. Gradetzke, S. Kankkunen, J. Becerra González, Y. Suda, Yukiho Kobayashi, Marcos López, S. Nozaki, J. Jiménez Quiles, Juan Escudero, D. Strom, T. Saito, S. Mangano, R. López-Coto, P. Majumdar, R. J. Garcı́a López, A. Abhishek, A. Lorini, D. Hadasch, J. Herrera Llorente, T. Yamamoto, K. Nilsson, F. Dazzi, P. Da Vela, D. Hrupec, S. Gasparyan, M. Makariev, W. Bednarek, Stefano Truzzi, V. Vitale, A. P. Marscher, Juan L. Contreras, E. Lindfors, A. Carosi, A. De Angelis, A. Lamastra, Ž. Bošnjak, A. Arbet Engels, R. Mirzoyan, F. Giordano, D. Paneque, A. Moralejo, María Láinez, R. Di Tria, P.G. Prada Moroni, C. Lorey, K. Abe, Tatsuya Nakaoka, M. Teshima, A. Dinesh, P.K.H. Yeung, D. Kerszberg, Colt Pauley, L. Barrios-Jiménez, F. Wersig, O. Domann, O. Koppitz, G. Manhalter, L. Nikolić
article en
3 citations

Abstract

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 ($ \gamma\prime_{\mathrm{min}}\gtrsim10^4 $), 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.

Astronomy and AstrophysicsVol. 695
University of Siena (IT), University of Pisa (IT), Boston University (US), Yamagata University (JP), Hiroshima University (JP), University of Geneva (CH), Tokyo Institute of Technology (JP), University of Rome Tor Vergata (IT), Obayashi (Japan) (JP), Universidad Complutense de Madrid (ES), Universitat Autònoma de Barcelona (ES), University of Udine (IT), Marshall Space Flight Center (US), Centre National de la Recherche Scientifique (FR), Tokai University (JP), A. Alikhanyan National Laboratory (AM), Universities Space Research Association (US), University of Padua (IT), University of Trieste (IT), University of Rijeka (HR), University of Turku (FI), Universidad de La Laguna (ES), Chiba University (JP), Konan University (JP), Saha Institute of Nuclear Physics (IN), University of Zagreb (HR), Turku Centre for Computer Science (FI), OsloMet – Oslo Metropolitan University (NO), University of Oslo (NO), Institute for High Energy Physics (ES), Homi Bhabha National Institute (IN), TU Dortmund University (DE), Université Paris Cité (FR), Kyoto University (JP), Bulgarian Academy of Sciences (BG), University of Würzburg (DE), Astronomical Observatory of Rome (IT), Agenzia Spaziale Italiana (IT), Deutsches Elektronen-Synchrotron DESY (DE), Laboratoire AstroParticule et Cosmologie (FR), University of Łódź (PL), ETH Zurich (CH), Max Planck Institute for Physics (DE), European Space Astronomy Centre (ES), Istituto Nazionale di Fisica Nucleare, Sezione di Torino (IT), Institute for Space Astrophysics and Planetology (IT), St. Marien-Hospital Bonn (DE), Istituto Nazionale di Fisica Nucleare, Sezione di Padova (IT), Istituto Nazionale di Fisica Nucleare, Sezione di Bari (IT), Istituto di Radioastronomia di Bologna (IT), Finnish Youth Research Society (FI), International Center for Relativistic Astrophysics (IT), Center for Astrophysics Harvard & Smithsonian (US), Centro Brasileiro de Pesquisas Físicas (BR), Instituto de Astrofísica de Canarias (ES), MVZ Labor Ravensburg (DE), International Center for Relativistic Astrophysics Network (AM), Port d'Informació Científica (ES), Instituto de Radioastronomía Milimétrica (ES), Istituto Nazionale di Fisica Nucleare, Sezione di Roma I (IT), Max Planck Institute for Radio Astronomy (DE), Instituto de Astrofísica de Andalucía (ES), Istituto Nazionale di Fisica Nucleare, Sezione di Pisa (IT), Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas (ES), University of Bergen (NO), University of Osijek (HR), University of Turin (IT), Nagoya University (JP), Liverpool John Moores University (GB), Polytechnic University of Bari (IT), Universitat de Barcelona (ES), The University of Tokyo (JP), Chiba Institute of Technology (JP), Sapienza University of Rome (IT), National Institute for Astrophysics (IT), Foundation for Research and Technology Hellas (GR), University of Split (HR), University of Oulu (FI)
National Science Foundation, Smithsonian Institution, U.S. Department of Energy, National Aeronautics and Space Administration, W. M. Keck Foundation, Centres de Recerca de Catalunya, European Commission, Deutsche Forschungsgemeinschaft, Ministry of Education, Culture, Sports, Science and Technology, Academia Sinica, Generalitat de Catalunya, Conselho Nacional de Desenvolvimento Científico e Tecnológico, Nuclear Safety and Security Commission, Agenzia Spaziale Italiana, Liverpool John Moores University, Vetenskapsrådet, Hrvatska Zaklada za Znanost, Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro, Centre National de la Recherche Scientifique, Istituto Nazionale di Astrofisica, High Energy Accelerator Research Organization, Junta de Andalucía, Ministério da Ciência, Tecnologia, Inovações e Comunicações, Istituto Nazionale di Fisica Nucleare, Instituto de Astrofísica de Andalucía, Marshall Space Flight Center, Goddard Space Flight Center, Smithsonian Astrophysical Observatory, Science and Technology Facilities Council, Consejo Superior de Investigaciones Científicas, Japan Aerospace Exploration Agency, Institut National de Physique Nucléaire et de Physique des Particules, Integrated Electronics Engineering Center, Binghamton University
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Astrophysics and Cosmic Phenomena
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