A1 Refereed original research article in a scientific journal
The IXPE and multifrequency polarimetric view of the extreme blazars 1ES 1101-232 and RGB J0710+591; 
Authors: Tavecchio, Fabrizio; Kim, Dawoon E.; Emery, Gabriel; Liodakis, Ioannis; Agudo, Iván; Coppi, Paolo; Tagliaferri, Giampiero; Di Gesu, Laura; Sbarrato, Tullia; Ballo, Lucia; Sciaccaluga, Alberto; Ehlert, Steven R.; Bonnoli, Giacomo; José Aceituno, Francisco; Casadio, Carolina; Casanova, Víctor; Donnarumma, Immacolata; Escudero, Juan; Morcuende, Daniel; Otero-Santos, Jorge; Sota, Alfredo; Piirola, Vilppu; Kouch, Pouya M.; Lindfors, Elina; Nilsson, Kari; Myserlis, Ioannis; Gurwell, Mark; Keating, Garrett; Rao, Ramprasad; Angelakis, Emmanouil; Kraus, Alexander; Imazawa, Ryo; Sasada, Mahito; Fukazawa, Yasushi; Kawabata, Koji S.; Uemura, Makoto; Mizuno, Tsunefumi; Nakaoka, Tatsuya; Tochihara, Sumie; Akai, Takahiro; Akitaya, Hiroshi; Bachev, Rumen; Strigachev, Anton; Benke, Petra; Debbrecht, Lena; Eich, Julia; Eppel, Florian; Gokus, Andrea; Hämmerich, Steven; Heßdörfer, Jonas; Kadler, Matthias; Kim, Sanghyun; Kirchner, Dana; Paraschos, Georgios Filippos; Rösch, Florian; Schulga, Wladislaw
Publisher: EDP Sciences
Publication year: 2026
Journal: Astronomy and Astrophysics
Article number: A150
Volume: 709
ISSN: 0004-6361
eISSN: 1432-0746
DOI: https://doi.org/10.1051/0004-6361/202558716
Publication's open availability at the time of reporting: Open Access
Publication channel's open availability : Open Access publication channel
Web address : https://doi.org/10.1051/0004-6361/202558716
Self-archived copy’s web address: https://research.utu.fi/converis/portal/detail/Publication/524879127
Self-archived copy's licence: CC BY
Self-archived copy's version: Publisher`s PDF
Multiwavelength polarimetry offers a powerful tool to probe magnetic field and flow geometries in the relativistic jets of blazars. Sources with synchrotron emission that spans a broad frequency range, from radio to X-rays, such as High Synchrotron Peak (HSP) type BL Lac objects, are particularly interesting. Previous measurements including radio, optical, and X-ray data show a clear trend, with the degree of polarization increasing with frequency. Here we report radio, optical, and X-ray observations (Swift, Nustar, and IXPE) of 1ES 1101-232 and RGB J0710+591, two blazars belonging to the puzzling subclass of extreme BL Lacs (EHBL). For 1ES 1101-232, we find a strong frequency dependence of the degree of polarization, with a ratio ΠX/ΠO ≃ 5.2. For RGB J0710+591, IXPE derives a 1σ upper limit ΠX < 11.6%, comparable to the measured optical degree of polarization (average ΠO ∼ 12%). We discuss the results in the framework of current interpretations and, in particular, we report an improved version of the stratified shock model that reproduces the observed data of both sources.
Keywords:
BL Lacertae objects: individual: 1ES 1101-232, BL Lacertae objects: individual: RGB J0710+591, radiation mechanisms: non-thermal
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We acknowledge financial support from a INAF Theory Grant 2024 (PI F. Tavecchio). This work has been funded by the European Union-Next Generation EU, PRIN 2022 RFF M4C21.1 (2022C9TNNX). We acknowledge financial support from ASI grant I/004/11/6. We thank Dr. Brad Cenko and the Swift team for approving and carrying out the Swift ToO observations. Part of this work is based on archival data provided by the Space Science Data Center-ASI. The IAA-CSIC co-authors acknowledge financial support from the Spanish “Ministerio de Ciencia e Innovación” (MCIN/AEI/ 10.13039/501100011033) through the Center of Excellence Severo Ochoa award for the Instituto de Astrofísica de Andalucía-CSIC (CEX2021-001131-S), and through grants PID2019-107847RB-C44 and PID2022-139117NB-C44. Some of the data are based on observations collected at the Observatorio de Sierra Nevada; which is owned and operated by the Instituto de Astrofísica de Andalucía (IAA-CSIC), and at the Centro Astronómico Hispano en Andalucía (CAHA); which is operated jointly by Junta de Andalucía and Consejo Superior de Investigaciones Científicas (IAA-CSIC). The Submillimeter Array is a joint project between the Smithsonian Astrophysical Observatory and the Academia Sinica Institute of Astronomy and Astrophysics and is funded by the Smithsonian Institution and the Academia Sinica. Maunakea, the location of the SMA, is a culturally important site for the indigenous Hawaiian people; we are privileged to study the cosmos from its summit. E.L. was supported by Academy of Finland projects 317636 and 320045. P.K. was supported by Academy of Finland projects 346071 and 345899. P.K. acknowledges support from the Metsähovi Radio Observatory of Aalto University. This work was supported by JST, the establishment of university fellowships towards the creation of science technology innovation, Grant Number JPMJFS2129. This work was supported by Japan Society for the Promotion of Science (JSPS) KAKENHI Grant Numbers JP21H01137. This work was also partially supported by Optical and Near-Infrared Astronomy Inter-University Cooperation Program from the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan. We are grateful to the observation and operating members of Kanata Telescope. I.L 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. The data in this study include observations made with the Nordic Optical Telescope, owned in collaboration by the University of Turku and Aarhus University, and operated jointly by Aarhus University, the University of Turku and the University of Oslo, representing Denmark, Finland and Norway, the University of Iceland and Stockholm University at the Observatorio del Roque de los Muchachos, La Palma, Spain, of the Instituto de Astrofisica de Canarias. The data presented here were obtained in part with ALFOSC, which is provided by the Instituto de Astrofísica de Andalucía (IAA) under a joint agreement with the University of Copenhagen and NOT. We acknowledge funding to support our NOT observations from the Finnish Centre for Astronomy with ESO (FINCA), University of Turku, Finland (Academy of Finland grant nr 306531). This research was partially supported by the Bulgarian National Science Fund of the Ministry of Education and Science under grants KP-06-H68/4 (2022), KP-06-H78/5 (2023) and KP-06-H88/4 (2024). Partly based on observations with the 100-m telescope of the MPIfR (Max-Planck-Institut für Radioastronomie) at Effelsberg. Observations with the 100-m radio telescope at Effelsberg have received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 101004719 (ORP). F.E., S.H., J.H., M.K., and F.R. acknowledge support from the Deutsche Forschungsgemeinschaft (DFG, grants 447572188, 434448349, 465409577). G. F. P. acknowledges support by the European Research Council advanced grant “M2FINDERS – Mapping Magnetic Fields with INterferometry Down to Event hoRizon Scales” (Grant No. 101018682). C.C. acknowledges support from the European Research Council (ERC) under the Horizon ERC Grants 2021 programme under grant agreement No. 101040021.
