arXiv · 2209.06227
Polarized Blazar X-rays imply particle acceleration in shocks
Abstract
Most of the light from blazars, active galactic nuclei with jets of magnetized plasma that point nearly along the line of sight, is produced by high-energy particles, up to $\sim 1$ TeV. Although the jets are known to be ultimately powered by a supermassive black hole, how the particles are accelerated to such high energies has been an unanswered question. The process must be related to the magnetic field, which can be probed by observations of the polarization of light from the jets. Measurements of the radio to optical polarization - the only range available until now - probe extended regions of the jet containing particles that left the acceleration site days to years earlier (Jorstad et al., 2005; Marin et al., 2018; Blinov et al., 2021), and hence do not directly explore the acceleration mechanism, as could X-ray measurements. Here we report the detection of X-ray polarization from the blazar Markarian~501 (Mrk~501). We measure an X-ray linear polarization degree $\Pi_X \sim10\%$, a factor of $\sim2$ higher than the value at optical wavelengths, with a polarization angle parallel to the radio jet. This points to a shock front as the source of particle acceleration, and also implies that the plasma becomes increasingly turbulent with distance from the shock.
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Ioannis Liodakis, Alan P. Marscher, Iván Agudo, Andrei V. Berdyugin, Maria I. Bernardos, Giacomo Bonnoli, George A. Borman, Carolina Casadio, Víctor Casanova, Elisabetta Cavazzuti, Nicole Rodriguez Cavero, Laura Di Gesu, Niccoló Di Lalla, Immacolata Donnarumma, Steven R. Ehlert, Manel Errando, Juan Escudero, Maya García-Comas, Beatriz Agís-González, César Husillos, Jenni Jormanainen, Svetlana G. Jorstad, Masato Kagitani, Evgenia N. Kopatskaya, Vadim Kravtsov, Henric Krawczynski, Elina Lindfors, Elena G. Larionova, Grzegorz M. Madejski, Frédéric Marin, Alessandro Marchini, Herman L. Marshall, Daria A. Morozova, Francesco Massaro, Joseph R. Masiero, Dimitri Mawet, Riccardo Middei, Maxwell A. Millar-Blanchaer, Ioannis Myserlis, Michela Negro, Kari Nilsson, Stephen L. O'Dell, Nicola Omodei, Luigi Pacciani, Alessandro Paggi, Georgia V. Panopoulou, Abel L. Peirson, Matteo Perri, Pierre-Olivier Petrucci, Juri Poutanen, Simonetta Puccetti, Roger W. Romani, Takeshi Sakanoi, Sergey S. Savchenko, Alfredo Sota, Fabrizio Tavecchio, Samaporn Tinyanont, Andrey A. Vasilyev, Zachary R. Weaver, Alexey V. Zhovtan, Lucio A. Antonelli, Matteo Bachetti, Luca Baldini, Wayne H. Baumgartner, Ronaldo Bellazzini, Stefano Bianchi, Stephen D. Bongiorno, Raffaella Bonino, Alessandro Brez, Niccoló Bucciantini, Fiamma Capitanio, Simone Castellano, Stefano Ciprini, Enrico Costa, Alessandra De Rosa, Ettore Del Monte, Alessandro Di Marco, Victor Doroshenko, Michal Dovčiak, Teruaki Enoto, Yuri Evangelista, Sergio Fabiani, Riccardo Ferrazzoli, Javier A. Garcia, Shuichi Gunji, Kiyoshi Hayashida, Jeremy Heyl, Wataru Iwakiri, Vladimir Karas, Takao Kitaguchi, Jeffery J. Kolodziejczak, Fabio La Monaca, Luca Latronico, Simone Maldera, Alberto Manfreda, Andrea Marinucci, Giorgio Matt, Ikuyuki Mitsuishi, Tsunefumi Mizuno, Fabio Muleri. 2022-09-13. Polarized Blazar X-rays imply particle acceleration in shocks. https://doi.org/10.1038/s41586-022-05338-0
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