Tracking Down the Broadband Polarimetric Properties of PG 1553+113;
: Middei, Riccardo; Jorstad, Svetlana G.; Marscher, Alan P.; Liodakis, Ioannis; Perri, Matteo; Maselli, Alessandro; Ciprini, Stefano; Nardini, Emanuele; Puccetti, Simonetta; Di Gesu, Laura; Agudo, Iván; Kim, Dawoon E.; Myserlis, Ioannis; Trindade Falcão, A.; Król, D. Ł.; Antonelli, Lucio A.; Aniello, Tommaso; Kouch, Pouya M.; Nilsson, Kari; Lindfors, Elina; Pursimo, Tapio; Aceituno, Francisco José; Casanova, Víctor; Emery, Gabriel; Escudero Pedrosa, Juan; Otero-Santos, Jorge; Sota, Alfredo; Piirola, Vilppu; Borman, George A.; Grishina, Tatiana S.; Hagen-Thorn, Vladimir A.; Kopatskaya, Evgenia N.; Larionova, Elena G.; Morozova, Daria A.; Savchenko, Sergey S.; Shishkina, Ekaterina V.; Troitskiy, Ivan S.; Troitskaya, Yulia V.; Vasilyev, Andrey A.; Zhovtan, Alexey V.; Benke, Petra; Debbrecht, Lena; Eich, Julia; Eppel, Florian; Gokus, Andrea; Hämmerich, Steven; Hessdörfer, Jonas; Kadler, Matthias; Kirchner, Dana; Paraschos, Georgios F.; Rösch, Florian; Schulga, Wladislaw; Gurwell, Mark; Keating, Garrett; Rao, Ramprasad; Angelakis, Emmanouil; Kraus, Alexander; Agís-González, Beatriz; Blinov, Dmitry; Glykopoulou, Anastasia; Capecchiacci, Sara; Floris, Alberto; Fotis, Panagiotis; Koukoutsi, Alkmini; Kypriotakis, John A.; Langis, Dimitrios A.; Rompogiannakis, Dimitrios; Polychronakis, Aristeidis; Tsioupli, Vasiliki; Vogiatzis, Stavros; Zoumpoulakis, Orestis; Tochihara, Sumie; Imazawa, Ryo; Sasada, Mahito; Fukazawa, Yasushi; Kawabata, Koji S.; Uemura, Makoto; Mizuno, Tsunefumi; Nakaoka, Tatsuya; Akitaya, Hiroshi; Akai, Takahiro
Publisher: Institute of Physics Publishing
: 2026
Astrophysical Journal
: 130
: 1004
: 1
: 0004-637X
: 1538-4357
DOI: https://doi.org/10.3847/1538-4357/ae6cf0
: https://doi.org/10.3847/1538-4357/ae6cf0
: https://research.utu.fi/converis/portal/detail/Publication/533831181
We report on a nine-month monitoring campaign of the blazar PG 1553+113, relying on three observations carried out in 2025 with the Imaging X-ray Polarimetry Explorer (IXPE) and supported by multiwavelength facilities. The source displayed pronounced variability across the electromagnetic spectrum, with X-ray flux changes by up to a factor of ∼5 and complex evolution of the optical polarization properties, including one of the largest (exceeding 150°) and fastest rotations in the electric vector position angle (EVPA) ever recorded. This swing of the EVPA was also accompanied by a temporary drop of the optical polarization degree to nearly zero. Significant X-ray polarization was observed during the third IXPE pointing, with a polarization degree ΠX = (18.4 ± 5.8)% and ΨX = 74° ± 9° in the 2–8 keV band, while only upper limits were obtained in the first two epochs. The optical data show that the second IXPE observation occurred shortly after a dramatic optical polarization event characterized by a rapid EVPA swing and strong depolarization. Two possible scenarios may explain the broadband polarimetric behavior: (i) the superposition of two emitting regions with nearly orthogonal magnetic field configurations and variable relative contributions, and (ii) the interaction of a single emitting region with a shock that temporarily reorders the magnetic field. In both cases, the data support a picture in which the X-ray and optical emissions arise from closely related but not strictly cospatial regions within a dynamically evolving, magnetically structured jet.
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We are grateful to the anonymous referee for valuable comments that improved this work. R.M. warmly thanks Enrico Piconcelli for useful comments and acknowledges financial support from the INAF Scientific Directorate. This work has been partially supported by the ASI-INAF program I/004/11/6. The Imaging X-ray Polarimetry Explorer (IXPE) is a joint US and Italian mission. The US contribution is supported by the National Aeronautics and Space Administration (NASA) and led and managed by its Marshall Space Flight Center (MSFC), with industry partner Ball Aerospace (contract NNM15AA18C). The Italian contribution is supported by the Italian Space Agency (Agenzia Spaziale Italiana, ASI) through contract ASI-OHBI-2022-13-I.0, agreements ASI-INAF-2022-19-HH.0 and ASI-INFN 2024-48-HH.0 ASI-INFN-2017.13-H0, and its Space Science Data Center (SSDC) with agreements ASI-INAF 2025-33-HH.0 and ASI-INFN 2026-5-HH.0, and by the Istituto Nazionale di Astrofisica (INAF) and the Istituto Nazionale di Fisica Nucleare (INFN) in Italy. This research used data products provided by the IXPE Team (MSFC, SSDC, INAF, and INFN) and distributed with additional software tools by the High-Energy Astrophysics Science Archive Research Center (HEASARC), at NASA Goddard Space Flight Center (GSFC). We acknowledge financial support from ASI-INAF agreement no. 2022-14-HH.0. 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 Perkins Telescope Observatory, located in Flagstaff, AZ, USA, is owned and operated by Boston University. The Boston University effort was supported by NASA IXPE Guest Observer grant 80NSSC25K0282. 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) and KP-06-H88/4 (2024). 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. The Submillimeter Array (SMA) 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. 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 program 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). This research was funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) as part of the DFG Research Unit FOR5195—project number 443220636. 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). The IAA-CSIC coauthors 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 Astrofíisica de Andalucía-CSIC (CEX2021-001131-S), and through grants PID2019-107847RB-C44 and PID2022-139117NB-C44. I.L., S.C, A.G., B.A.-G., A.F., D.A.L., J.A.K., D.R., and O.Z. were 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. E.L. was supported by Academy of Finland projects 317636 and 320045. 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 No. 306531). This research has made use of data from the RoboPol program, a collaboration between Caltech, the University of Crete, IA-FORTH, IUCAA, the MPIfR, and the Nicolaus Copernicus University, which was conducted at Skinakas Observatory in Crete, Greece. This work was supported by JST, the establishment of university fellowships toward the creation of science technology innovation, grant No. JPMJFS2129. This work was supported by Japan Society for the Promotion of Science (JSPS) KAKENHI grant No. 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.
