Fabrizio Tavecchio, Dawoon E. Kim, Gabriel Emery, Ioannis Liodakis, Iván Agudo, Paolo Coppi, Giampiero Tagliaferri, Laura Di Gesu, T. Sbarrato, Lucia Ballo, A. Sciaccaluga, Steven R. Ehlert, Giacomo Bonnoli, F. J. Aceituno, Carolina Casadio Víctor Casanova, Víctor Casanova, Immacolata Donnarumma, Juan Escudero, Daniel González Morcuende, Jorge Otero-Santos, A. Sota, V. Piirola, Pouya M. Kouch, E. Lindfors, Kari Nilsson, Ioannis Myserlis, Mark Gurwell, Garrett Keating, Ramprasad Rao, E. Angelakis, Alexander Kraus, Ryo Imazawa, Mahito Sasada, Yasushi Fukazawa, Koji S. Kawabata, Makoto Uemura, Tsunefumi Mizuno, Tatsuya Nakaoka, Sumie Tochihara, T. Akai, Hiroshi Akitaya, Rumen Bachev, A. Strigachev, P. Benke, Lena Debbrecht, J. Eich, Florian Eppel, Andrea Gokus, Steven Hammerich, Jonas Heß dörfer, Matthias Kadler, Sanghyun Kim, Dana Kirchner, Georgios Filippos Paraschos, F. Rösch, Wladislaw Schulga
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 Π X /Π O ≃ 5.2. For RGB J0710+591, IXPE derives a 1 σ upper limit Π X < 11.6%, comparable to the measured optical degree of polarization (average Π O ∼ 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.