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arXiv · 2510.16109

Detection of Compton scattering in the jet of 3C 84

Ioannis Liodakis·Sudip Chakraborty·Frédéric Marin·Steven R. Ehlert·Thibault Barnouin·Pouya M. Kouch·Kari Nilsson·Elina Lindfors·Tapio Pursimo·Georgios F. Paraschos·Riccardo Middei·Anna Trindade Falcão·Svetlana Jorstad·Iván Agudo·Yuri Y. Kovalev·Jacob J. Casey·Laura Di Gesu·Philip Kaaret·Dawoon E. Kim·Fabian Kislat·Ajay Ratheesh·M. Lynne Saade·Francesco Tombesi·Alan Marscher·Francisco José Aceituno·Giacomo Bonnoli·Víctor Casanova·Gabriel Emery·Juan Escudero Pedrosa·Daniel Morcuende·Jorge Otero-Santos·Alfredo Sota·Vilppu Piirola·Rumen Bachev·Anton Strigachev·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·Ioannis Myserlis·Mark Gurwell·Garrett Keating·Ramprasad Rao·Sincheol Kang·Sang-Sung Lee·Sanghyun Kim·Whee Yeon Cheong·Hyeon-Woo Jeong·Chanwoo Song·Shan Li·Myeong-Seok Nam·Diego Álvarez-Ortega·Carolina Casadio·Emmanouil Angelakis·Alexander Kraus·Jenni Jormanainen·Vandad Fallah Ramazani·Chien-Ting Chen·Enrico Costa·Eugene Churazov·Riccardo Ferrazzoli·Giorgio Galanti·Ildar Khabibulin·Stephen L. O'Dell·Luigi Pacciani·Marco Roncadelli·Oliver J. Roberts·Paolo Soffitta·Douglas A. Swartz·Fabrizio Tavecchio·Martin C. Weisskopf·Irina Zhuravleva
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Abstract

3C 84 is the brightest cluster galaxy in the Perseus Cluster. It is among the closest radio-loud active galaxies and among the very few that can be detected from low frequency radio up to TeV $\gamma$-rays. Here we report on the first X-ray polarization observation of 3C~84 with the Imaging X-ray Polarimetry Explorer, for a total of 2.2 Msec that coincides with a flare in $\gamma$-rays. This is the longest observation for a radio-loud active galaxy that allowed us to reach unprecedented sensitivity, leading to the detection of an X-ray polarization degree of $\rm\Pi_X=4.2\pm1.3\%$ ($\sim3.2\sigma$ confidence) at an X-ray electric vector polarization angle of $\rm \psi_X=163^{\circ}\pm9^{\circ}$, that is aligned with the radio jet direction on the sky. Optical polarization observations show fast variability about the jet axis as well. Our results strongly favor models in which X-rays are produced by Compton scattering from relativistic electrons -- specifically Synchrotron Self-Compton -- that takes places downstream, away from the supermassive black hole.

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Ioannis Liodakis, Sudip Chakraborty, Frédéric Marin, Steven R. Ehlert, Thibault Barnouin, Pouya M. Kouch, Kari Nilsson, Elina Lindfors, Tapio Pursimo, Georgios F. Paraschos, Riccardo Middei, Anna Trindade Falcão, Svetlana Jorstad, Iván Agudo, Yuri Y. Kovalev, Jacob J. Casey, Laura Di Gesu, Philip Kaaret, Dawoon E. Kim, Fabian Kislat, Ajay Ratheesh, M. Lynne Saade, Francesco Tombesi, Alan Marscher, Francisco José Aceituno, Giacomo Bonnoli, Víctor Casanova, Gabriel Emery, Juan Escudero Pedrosa, Daniel Morcuende, Jorge Otero-Santos, Alfredo Sota, Vilppu Piirola, Rumen Bachev, Anton Strigachev, 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, Ioannis Myserlis, Mark Gurwell, Garrett Keating, Ramprasad Rao, Sincheol Kang, Sang-Sung Lee, Sanghyun Kim, Whee Yeon Cheong, Hyeon-Woo Jeong, Chanwoo Song, Shan Li, Myeong-Seok Nam, Diego Álvarez-Ortega, Carolina Casadio, Emmanouil Angelakis, Alexander Kraus, Jenni Jormanainen, Vandad Fallah Ramazani, Chien-Ting Chen, Enrico Costa, Eugene Churazov, Riccardo Ferrazzoli, Giorgio Galanti, Ildar Khabibulin, Stephen L. O'Dell, Luigi Pacciani, Marco Roncadelli, Oliver J. Roberts, Paolo Soffitta, Douglas A. Swartz, Fabrizio Tavecchio, Martin C. Weisskopf, Irina Zhuravleva. 2025-10-17. Detection of Compton scattering in the jet of 3C 84. https://doi.org/10.3847/2041-8213%2Fae157d

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