arXiv · 2605.12602
Tracking down the broadband polarimetric properties of PG 1553+113
Abstract
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 multi-wavelength facilities. The source displayed pronounced variability across the electromagnetic spectrum, with X-ray flux changes by up to a factor of $\sim5$ and complex evolution of the optical polarization properties, including one of the largest (exceeding $150^{\circ}$) 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 $\Pi_{\rm X}\,=(\,18.4\,\pm\,5.8)\%$ and $\Psi_{\rm X}\,=\,74^{\circ} \pm 9^{\circ}$ 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 co-spatial regions within a dynamically evolving, magnetically structured jet.
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Riccardo Middei, Svetlana G. Jorstad, Alan P. Marscher, Ioannis Liodakis, Matteo Perri, Alessandro Maselli, Stefano Ciprini, Emanuele Nardini, Simonetta Puccetti, Laura Di Gesu, Iván Agudo, Dawoon E. Kim, Ioannis Myserlis, A. Trindade Falcão, D. Ł. Król, Lucio A. Antonelli, Tommaso Aniello, Pouya M. Kouch, Kari Nilsson, Elina Lindfors, Tapio Pursimo, Francisco José Aceituno, Víctor Casanova, Gabriel Emery, Juan Escudero Pedrosa, Jorge Otero-Santos, Alfredo Sota, Vilppu Piirola, George A. Borman, Tatiana S. Grishina, Vladimir A. Hagen-Thorn, Evgenia N. Kopatskaya, Elena G. Larionova, Daria A. Morozova, Sergey S. Savchenko, Ekaterina V. Shishkina, Ivan S. Troitskiy, Yulia V. Troitskaya, Andrey A. Vasilyev, Alexey V. Zhovtan, Petra Benke, Lena Debbrecht, Julia Eich, Florian Eppel, Andrea Gokus, Steven Hämmerich, Jonas Heßdörfer, Matthias Kadler, Dana Kirchner, Georgios F. Paraschos, Florian Rösch, Wladislaw Schulga, Mark Gurwell, Garrett Keating, Ramprasad Rao, Emmanouil Angelakis, Alexander Kraus, Beatriz Agís-González, Dmitry Blinov, Anastasia Glykopoulou, Sara Capecchiacci, Alberto Floris, Panagiotis Fotis, Alkmini Koukoutsi, John A. Kypriotakis, Dimitrios A. Langis, Dimitrios Rompogiannakis, Aristeidis Polychronakis, Vasiliki Tsioupli, Stavros Vogiatzis, Orestis Zoumpoulakis, Sumie Tochihara, Ryo Imazawa, Mahito Sasada, Yasushi Fukazawa, Koji S. Kawabata, Makoto Uemura, Tsunefumi Mizuno, Tatsuya Nakaoka, Hiroshi Akitaya, Takahiro Akai. 2026-05-12. Tracking down the broadband polarimetric properties of PG 1553+113. https://arxiv.org/abs/2605.12602
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