Very high-energy gamma-ray detection and long-term multiwavelength view of the flaring blazar B2 1811+31

Abe, K.; Abe, S.; Abhir, J.; Abhishek, A.; Acciari, V. A.; Aguasca-Cabot, A.; Agudo, I.; Aniello, T.; Ansoldi, S.; Antonelli, L. A.; Arbet Engels, A.; Arcaro, C.; Asano, K.; Babić, A.; Barres de Almeida, U.; Barrio, J. A.; Barrios-Jiménez, L.; Batković, I.; Baxter, J.; Becerra González, J.; Bednarek, W.; Bernardini, E.; Bernete, J.; Berti, A.; Besenrieder, J.; Bigongiari, C.; Biland, A.; Blanch, O.; Bonnoli, G.; Bošnjak, Ž.; Bronzini, E.; Burelli, I.; Campoy-Ordaz, A.; Carosi, A.; Carosi, R.; Carretero-Castrillo, M.; Castro-Tirado, A. J.; Cerasole, D.; Ceribella, G.; Chilingarian, A.; Cifuentes, A.; Colombo, E.; Contreras, J. L.; Cortina, J.; Covino, S.; D'Ammando, F.; D'Amico, G.; Da Vela, P.; Dazzi, F.; De Angelis, A.; De Lotto, B.; de Menezes, R.; Delfino, M.; Delgado, J.; Delgado Mendez, C.; Di Pierro, F.; Di Tria, R.; Di Venere, L.; Dinesh, A.; Dominis Prester, D.; Donini, A.; Dorner, D.; Doro, M.; Eisenberger, L.; Elsaesser, D.; Escudero, J.; Fariña, L.; Foffano, L.; Font, L.; Fröse, S.; Fukazawa, Y.; García López, R. J.; Garczarczyk, M.; Gasparyan, S.; Gaug, M.; Giesbrecht Paiva, J. G.; Giglietto, N.; Giordano, F.; Gliwny, P.; Gradetzke, T.; Grau, R.; Green, D.; Green, J. G.; Günther, P.; Hadasch, D.; Hahn, A.; Hassan, T.; Heckmann, L.; Herrera Llorente, J.; Hrupec, D.; Imazawa, R.; Israyelyan, D.; Itokawa, T.; Jiménez Martínez, I.; Jiménez Quiles, J.; Jormanainen, J.; Kankkunen, S.; Kayanoki, T.; Kerszberg, D.; Khachatryan, M.; Kluge, G. W.; Kobayashi, Y.; Konrad, J.; Kouch, P. M.; Kubo, H.; Kushida, J.; Láinez, M.; Lamastra, A.; Lindfors, E.; Lombardi, S.; Longo, F.; López-Coto, R.; López-Moya, M.; López-Oramas, A.; Loporchio, S.; Lorini, A.; Lulić, L.; Lyard, E.; Majumdar, P.; Makariev, M.; Maneva, G.; Manganaro, M.; Mangano, S.; Mannheim, K.; Mariotti, M.; Martínez, M.; Maruševec, P.; Mas-Aguilar, A.; Mazin, D.; Menchiari, S.; Mender, S.; Miceli, D.; Miranda, J. M.; Mirzoyan, R.; Molero González, M.; Molina, E.; Mondal, H. A.; Moralejo, A.; Nakamori, T.; Nanci, C.; Neustroev, V.; Nickel, L.; Nievas Rosillo, M.; Nigro, C.; Nikolić, L.; Nilsson, K.; Nishijima, K.; Njoh Ekoume, T.; Noda, K.; Nozaki, S.; Okumura, A.; Paiano, S.; Paneque, D.; Paoletti, R.; Paredes, J. M.; Pavletić, L.; Peresano, M.; Persic, M.; Pihet, M.; Pirola, G.; Podobnik, F.; Prada Moroni, P. G.; Prandini, E.; Principe, G.; Rhode, W.; Ribó, M.; Rico, J.; Righi, C.; Sahakyan, N.; Saito, T.; Saturni, F. G.; Schmitz, K.; Schmuckermaier, F.; Schubert, J. L.; Sciaccaluga, A.; Silvestri, G.; Sitarek, J.; Sliusar, V.; Sobczynska, D.; Stamerra, A.; Strišković, J.; Strom, D.; Strzys, M.; Suda, Y.; Tajima, H.; Takahashi, M.; Takeishi, R.; Temnikov, P.; Terauchi, K.; Terzić, T.; Teshima, M.; Tutone, A.; Ubach, S.; van Scherpenberg, J.; Vazquez Acosta, M.; Ventura, S.; Verna, G.; Viale, I.; Vigliano, A.; Vigorito, C. F.; Vitale, V.; Vovk, I.; Walter, R.; Wersig, F.; Will, M.; Yamamoto, T.; Bartolini, C.; Bissaldi, E.; Garrappa, S.; Ankara, E.; Bader, N.; Feige, M.; Hümmer, F.; Kaplan, F.; Lorey, C.; Reinhart, D.; Schoch, K.; Steineke, R.; Marchini, A.; Fallah Ramazani, V.; Graham, M. J.; Hovatta, T.; Kiehlmann, S.; Readhead, A. C. S.; Benke, P.; Eppel, F.; Hämmerich, S.; Heßdörfer, J.; Kadler, M.; Kirchner, D.; Gokus, A.; Paraschos, G. F.; Rösch, F.; Sinapius, J.

doi:10.1051/0004-6361/202452942

Published May 2025 | Version Published

Journal Article Open

Very high-energy gamma-ray detection and long-term multiwavelength view of the flaring blazar B2 1811+31

1. Tokai University
2. University of Tokyo
3. ETH Zurich
4. University of Siena
5. Institute for High Energy Physics
6. University of Barcelona
7. Instituto de Astrofísica de Andalucía
8. National Institute for Astrophysics
9. University of Udine
10. Max Planck Institute for Physics
11. University of Padua
12. University of Zagreb
13. Centro Brasileiro de Pesquisas Físicas
14. Complutense University of Madrid
15. University of La Laguna
16. University of Łódź
17. Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas
18. Autonomous University of Barcelona
19. University of Pisa
20. INFN Sezione di Bari
21. Armenian MAGIC Group: A. Alikhanyan National Science Laboratory, 0036, Yerevan, Armenia
22. Istituto di Radioastronomia di Bologna
23. University of Bergen
24. University of Turin
25. University of Rijeka
26. University of Würzburg
27. TU Dortmund University
28. Hiroshima University
29. Deutsches Elektronen-Synchrotron DESY
30. Armenian MAGIC Group: ICRANet-Armenia, 0019, Yerevan, Armenia
31. Astroparticle and Cosmology Laboratory
32. University of Osijek
33. University of Turku
34. University of Oslo
35. University of Trieste
36. University of Geneva
37. Saha Institute of Nuclear Physics
38. Institute for Nuclear Research and Nuclear Energy
39. Yamagata University
40. University of Oulu
41. Chiba University
42. Nagoya University
43. Kyoto University
44. National Institute for Nuclear Physics
45. Konan University
46. University of Trento
47. Polytechnic University of Bari
48. Weizmann Institute of Science
49. Hans-Haffner-Sternwarte (Hettstadt), Naturwissenschaftliches Labor für Schüler am FKG, Friedrich-Koenig-Gymnasium, D-97082, Würzburg, Germany
50. California Institute of Technology
51. Aalto University
52. Max Planck Institute for Radio Astronomy
53. University of Erlangen-Nuremberg
54. Washington University in St. Louis

Context. Among the blazars whose emission has been detected up to very high-energy (VHE; 100 GeV<E<100 TeV) γ rays, intermediate synchrotron-peaked BL Lacs (IBLs) are quite rare. The IBL B2 1811+31 (z = 0.117) exhibited intense flaring activity in 2020. Detailed characterization of the source emission from radio to γ-ray energies was achieved with quasi-simultaneous observations, which led to the first-time detection of VHE γ-ray emission from the source with the MAGIC telescopes.

Aims. In this work, we present a comprehensive multiwavelength (MWL) view of B2 1811+31, with a specific focus on the 2020 VHE flare, employing data from MAGIC, Fermi-LAT, Swift-XRT, Swift-UVOT, and several optical and radio ground-based telescopes.

Methods. Long-term MWL data were employed to contextualize the high-state episode within the source emissions over 18 years. We investigated the variability, cross-correlations, and classification of the source emissions during low and high states. We propose an interpretative leptonic model for the observed radiative high state.

Results. During the 2020 flaring state, the synchrotron peak frequency shifted to higher values and reached the limit of the IBL classification. Variability in timescales of a few hours in the high-energy (HE; 100 MeV<E<100 GeV) γ-ray band poses an upper limit of 6×10¹⁴ δ_D cm on the size of the emission region responsible for the γ-ray flare, with δ_D being the relativistic Doppler factor of the region. During the 2020 high state, the average spectrum became harder in the HE γ-ray band compared to the low states. A similar behavior has been observed in X-rays. Conversely, during different activity periods, we find harder-when-brighter trends in X-rays and a hint of softer-when-brighter trends at HE γ rays. A long-term HE γ-ray and optical correlation indicates that the same emission regions dominate the radiative output in both ranges, whereas the evolution at 15 GHz shows no correlation with the fluxes at higher frequencies. We test one-zone and two-zone synchrotron-self-Compton models for describing the broadband spectral energy distribution during the 2020 flaring state and investigate the self-consistency of the proposed scenario.

Copyright and License

© 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.

Acknowledgement

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, MPG and HGF; the Italian INFN and INAF; the Swiss National Fund SNF; the grants PID2019-104114RB-C31, PID2019-104114RB-C32, PID2019-104114RB-C33, PID2019-105510GB-C31, PID2019-107847RB-C41, PID2019-107847RB-C42, PID2019-107847RB-C44, PID2019-107988GB-C22, PID2022-136828NB-C41, PID2022-137810NB-C22, PID2022-138172NB-C41, PID2022-138172NB-C42, PID2022-138172NB-C43, PID2022-139117NB-C41, PID2022-139117NB-C42, PID2022-139117NB-C43, PID2022-139117NB-C44 funded by the Spanish MCIN/AEI/ 10.13039/501100011033 and “ERDF A way of making Europe”; 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 DO1-400/18.12.2020 and the Academy of Finland grant nr. 320045 is gratefully acknowledged. This work was also been supported by Centros de Excelencia “Severo Ochoa” y Unidades “María de Maeztu” program of the Spanish MCIN/AEI/ 10.13039/501100011033 (CEX2019-000920-S, CEX2019-000918-M, CEX2021-001131-S) and by the CERCA institution and grants 2021SGR00426 and 2021SGR00773 of the Generalitat de Catalunya; by the Croatian Science Foundation (HrZZ) Project IP-2022-10-4595 and the University of Rijeka Project uniri-prirod-18-48; by the Deutsche Forschungsgemeinschaft (SFB1491) and by the Lamarr-Institute for Machine Learning and Artificial Intelligence; by the Polish Ministry Of Education and Science grant No. 2021/WK/08; and by the Brazilian MCTIC, CNPq and FAPERJ. 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 performed in part under DOE Contract DE-AC02-76SF00515. We acknowledge the use of public data from the Swift data archive. This work has made use of data from the Joan Oró Telescope (TJO) of the Montsec Observatory (OdM), which is owned by the Catalan Government and operated by the Institute for Space Studies of Catalonia (IEEC). This research has made use of data from the OVRO 40-m monitoring program (Richards et al. 2011), supported by private funding from the California Institute of Technology and the Max Planck Institute for Radio Astronomy, and by NASA grants NNX08AW31G, NNX11A043G, and NNX14AQ89G and NSF grants AST-0808050 and AST-1109911. S.K. was funded by the European Union ERC-2022-STG – BOOTES – 101076343. Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the European Research Council Executive Agency. Neither the European Union nor the granting authority can be held responsible for them. This work is based on observations with the 100-m telescope of the MPIfR (Max-Planck-Institut für Radioastronomie) at Effelsberg.

Contributions

D. Cerasole: project leadership, Fermi-LAT data analysis, Swift data analysis, multiwavelength data analysis, theoretical modeling and interpretation, paper drafting and editing; L. Di Venere: supervising the Fermi-LAT analysis, paper editing; T. Hovatta: OVRO data analysis; E. Lindfors: optical data analysis and collection, theoretical interpretation, paper drafting and editing; S. Loporchio: MAGIC data analysis, theoretical interpretation, paper drafting and editing; S. Kiehlmann: OVRO data analysis; P. Kouch: optical data analysis and collection; L. Pavletic: MAGIC analysis cross-check; A. C. S. Readhead: OVRO data analysis. The rest of the authors have contributed in one or several of the following ways: design, construction, maintenance and operation of the instrument(s); preparation and/or evaluation of the observation proposals; data acquisition, processing, calibration and/or reduction; production of analysis tools and/or related Monte Carlo simulations; discussion and approval of the contents of the draft.

Data Availability

All data shown in Figures 1, 2, 3, 4, 5, 9, 10 and 11 are available at the CDS via anonymous ftp to cdsarc.cds.unistra.fr (130.79.128.5) or via https://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/697/A172

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Is new version of: Discussion Paper: arXiv:2503.19054 (arXiv)
Is supplemented by: Dataset: https://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/697/A172 (URL)

Federal Ministry of Education and Research
Max Planck Society
Istituto Nazionale di Fisica Nucleare
National Institute for Astrophysics
Swiss National Science Foundation
Ministerio de Ciencia, Innovación y Universidades
PID2019-104114RB-C31
Ministerio de Ciencia, Innovación y Universidades
PID2019-104114RB-C32
Ministerio de Ciencia, Innovación y Universidades
PID2019-104114RB-C33
Ministerio de Ciencia, Innovación y Universidades
PID2019-105510GB-C31
Ministerio de Ciencia, Innovación y Universidades
PID2019-107847RB-C41
Ministerio de Ciencia, Innovación y Universidades
PID2019-107847RB-C42
Ministerio de Ciencia, Innovación y Universidades
PID2019-107847RB-C44
Ministerio de Ciencia, Innovación y Universidades
PID2019-107988GB-C22
Ministerio de Ciencia, Innovación y Universidades
PID2022-136828NB-C41
Ministerio de Ciencia, Innovación y Universidades
PID2022-137810NB-C22
Ministerio de Ciencia, Innovación y Universidades
PID2022-138172NB-C41
Ministerio de Ciencia, Innovación y Universidades
PID2022-138172NB-C42
Ministerio de Ciencia, Innovación y Universidades
PID2022-138172NB-C43
Ministerio de Ciencia, Innovación y Universidades
PID2022-139117NB-C41
Ministerio de Ciencia, Innovación y Universidades
PID2022-139117NB-C42
Ministerio de Ciencia, Innovación y Universidades
PID2022-139117NB-C43
Ministerio de Ciencia, Innovación y Universidades
PID2022-139117NB-C44
Department of Atomic Energy
Institute for Cosmic Ray Research
The University of Tokyo
Japan Society for the Promotion of Science
Ministry of Education, Culture, Sports, Science and Technology
Ministry of Education and Science
Research Council of Finland
DO1-400/18.12.2020
Research Council of Finland
320045
Ministerio de Ciencia, Innovación y Universidades
CEX2019-000920-S
Ministerio de Ciencia, Innovación y Universidades
CEX2019-000918-M
Ministerio de Ciencia, Innovación y Universidades
CEX2021-001131-S
CERCA Institution
Government of Catalonia
2021SGR00426
Government of Catalonia
2021SGR00773
Croatian Science Foundation
IP-2022-10-4595
University of Rijeka
uniri-prirod-18-48
Deutsche Forschungsgemeinschaft
SFB1491
Lamarr Institute
Ministry of Science and Higher Education
2021/WK/08
Ministry of Science, Technology and Innovation
National Council for Scientific and Technological Development
Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro
United States Department of Energy
DE-AC02-76SF00515
National Aeronautics and Space Administration
NNX08AW31G
National Aeronautics and Space Administration
NNX11A043G
National Aeronautics and Space Administration
NNX14AQ89G
National Science Foundation
AST-0808050
National Science Foundation
AST-1109911
European Research Council
BOOTES 101076343

Accepted: 2025-03-20
Available: 2025-05-20

Published online

Caltech groups: Astronomy Department, Owens Valley Radio Observatory, Division of Physics, Mathematics and Astronomy (PMA)
Publication Status: Published

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Very high-energy gamma-ray detection and long-term multiwavelength view of the flaring blazar B2 1811+31

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Very high-energy gamma-ray detection and long-term multiwavelength view of the flaring blazar B2 1811+31

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