Polarized Blazar X-rays imply particle acceleration in shocks
Creators: name: Liodakis, Ioannis
name: Marscher, Alan P.
name: Agudo, Iván
name: Berdyugin, Andrei V.
name: Bernardos, Maria I.
name: Bonnoli, Giacomo
name: Borman, George A.
name: Casadio, Carolina
name: Casanova, Víctor
name: Cavazzuti, Elisabetta
name: Cavero, Nicole Rodriguez
name: Di Gesu, Laura
name: Di Lalla, Niccoló
name: Donnarumma, Immacolata
name: Ehlert, Steven R.
name: Errando, Manel
name: Escudero, Juan
name: García-Comas, Maya
name: Agís-González, Beatriz
name: Husillos, César
name: Jormanainen, Jenni
name: Jorstad, Svetlana G.
name: Kagitani, Masato
name: Kopatskaya, Evgenia N.
name: Kravtsov, Vadim
name: Krawczynski, Henric
name: Lindfors, Elina
name: Larionova, Elena G.
name: Madejski, Grzegorz M.
name: Marin, Frédéric
name: Marchini, Alessandro
name: Marshall, Herman L.
name: Morozova, Daria A.
name: Massaro, Francesco
name: Masiero, Joseph R.
name: Mawet, Dimitri
name: Middei, Riccardo
name: Millar-Blanchaer, Maxwell A.
name: Myserlis, Ioannis
name: Negro, Michela
name: Nilsson, Kari
name: O'Dell, Stephen L.
name: Omodei, Nicola
name: Pacciani, Luigi
name: Paggi, Alessandro
name: Panopoulou, Georgia V.
name: Peirson, Abel L.
name: Perri, Matteo
name: Petrucci, Pierre-Olivier
name: Poutanen, Juri
name: Puccetti, Simonetta
name: Romani, Roger W.
name: Sakanoi, Takeshi
name: Savchenko, Sergey S.
name: Sota, Alfredo
name: Tavecchio, Fabrizio
name: Tinyanont, Samaporn
name: Vasilyev, Andrey A.
name: Weaver, Zachary R.
name: Zhovtan, Alexey V.
name: Antonelli, Lucio A.
name: Bachetti, Matteo
name: Baldini, Luca
name: Baumgartner, Wayne H.
name: Bellazzini, Ronaldo
name: Bianchi, Stefano
name: Bongiorno, Stephen D.
name: Bonino, Raffaella
name: Brez, Alessandro
name: Bucciantini, Niccoló
name: Capitanio, Fiamma
name: Castellano, Simone
name: Ciprini, Stefano
name: Costa, Enrico
name: De Rosa, Alessandra
name: Del Monte, Ettore
name: Di Marco, Alessandro
name: Doroshenko, Victor
name: Dovčiak, Michal
name: Enoto, Teruaki
name: Evangelista, Yuri
name: Fabiani, Sergio
name: Ferrazzoli, Riccardo
name: Garcia, Javier A.
name: Gunji, Shuichi
name: Hayashida, Kiyoshi
name: Heyl, Jeremy
name: Iwakiri, Wataru
name: Karas, Vladimir
name: Kitaguchi, Takao
name: Kolodziejczak, Jeffery J.
name: La Monaca, Fabio
name: Latronico, Luca
name: Maldera, Simone
name: Manfreda, Alberto
name: Marinucci, Andrea
name: Matt, Giorgio
name: Mitsuishi, Ikuyuki
name: Mizuno, Tsunefumi
name: Muleri, Fabio
name: Ng, Stephen C. -Y.
name: Oppedisano, Chiara
name: Papitto, Alessandro
name: Pavlov, George G.
name: Pesce-Rollins, Melissa
name: Pilia, Maura
name: Possenti, Andrea
name: Ramsey, Brian D.
name: Rankin, John
name: Ratheesh, Ajay
name: Sgró, Carmelo
name: Slane, Patrick
name: Soffitta, Paolo
name: Spandre, Gloria
name: Tamagawa, Toru
name: Taverna, Roberto
name: Tawara, Yuzuru
name: Tennant, Allyn F.
name: Thomas, Nicolas E.
name: Tombesi, Francesco
name: Trois, Alessio
name: Tsygankov, Sergey
name: Turolla, Roberto
name: Vink, Jacco
name: Weisskopf, Martin C.
name: Wu, Kinwah
name: Xie, Fei
name: Zane, Silvia
Publisher: name: arXiv
Year: 2022
Subjects: subject: High Energy Astrophysical Phenomena (astro-ph.HE)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: 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 $Π_X \sim10\%$, 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.
description: 34 pages, 4 figures, 4 tables