학술논문
Discovery of X-ray polarization angle rotation in active galaxy Mrk 421
Document Type
Working Paper
Author
Di Gesu, Laura; Marshall, Herman L.; Ehlert, Steven R.; Kim, Dawoon E.; Donnarumma, Immacolata; Tavecchio, Fabrizio; Liodakis, Ioannis; Kiehlmann, Sebastian; Agudo, Iván; Jorstad, Svetlana G.; Muleri, Fabio; Marscher, Alan P.; Puccetti, Simonetta; Middei, Riccardo; Perri, Matteo; Pacciani, Luigi; Negro, Michela; Romani, Roger W.; Di Marco, Alessandro; Blinov, Dmitry; Bourbah, Ioakeim G.; Kontopodis, Evangelos; Mandarakas, Nikos; Romanopoulos, Stylianos; Skalidis, Raphael; Vervelaki, Anna; Casadio, Carolina; Escudero, Juan; Myserlis, Ioannis; Gurwell, Mark; Rao, Ramprasad; Keating, Garrett; Kouch, Pouya M.; Lindfors, Elina; Aceituno, Francisco Josè; Bernardos, Maria I.; Bonnoli, Giacomo; Casanova, Vìctor; Garcìa-Comas, Maya; Agìs-Gonzàlez, Beatriz; Husillos, Cèsar; Marchini, Alessandro; Sota, Alfredo; Imazawa, Ryo; Sasada, Mahito; Fukazawa, Yasushi; Kawabata, Koji S.; Uemura, Makoto; Mizuno, Tsunefumi; Nakaoka, Tatsuya; Akitaya, Hiroshi; Savchenko, Sergey S.; Vasilyev, Andrey A.; Gòmez, Josè L.; Antonelli, Lucio A.; Barnouin, Thibault; Bonino, Raffaella; Cavazzuti, Elisabetta; Costamante, Luigi; Chen, Chien-Ting; Cibrario, Nicolò; De Rosa, Alessandra; Di Pierro, Federico; Errando, Manel; Kaaret, Philip; Karas, Vladimir; Krawczynski, Henric; Lisalda, Lindsey; Madejski, Grzegorz; Malacaria, Christian; Marin, Frédéric; Marinucci, Andrea; Massaro, Francesco; Matt, Giorgio; Mitsuishi, Ikuyuki; O'Dell, Stephen L.; Paggi, Alessandro; Peirson, Abel L.; Petrucci, Pierre-Olivier; Ramsey, Brian D.; Tennant, Allyn F.; Wu, Kinwah; Bachetti, Matteo; Baldini, Luca; Baumgartner, Wayne H.; Bellazzini, Ronaldo; Bianchi, Stefano; Bongiorno, Stephen D.; Brez, Alessandro; Bucciantini, Niccolò; Capitanio, Fiamma; Castellano, Simone; Ciprini, Stefano; Costa, Enrico; Del Monte, Ettore; Di Lalla, Niccolò; Doroshenko, Victor; Dovčiak, Michal; Enoto, Teruaki; Evangelista, Yuri; Fabiani, Sergio; Ferrazzoli, Riccardo; Garcia, Javier A.; Gunji, Shuichi; Hayashida, Kiyoshi; Heyl, Jeremy; Iwakiri, Wataru; Kislat, Fabian; Kitaguchi, Takao; Kolodziejczak, Jeffery J.; La Monaca, Fabio; Latronico, Luca; Maldera, Simone; Manfreda, Alberto; Ng, C. -Y.; Omodei, Nicola; Oppedisano, Chiara; Papitto, Alessandro; Pavlov, George G.; Pesce-Rollins, Melissa; Pilia, Maura; Possenti, Andrea; Poutanen, Juri; Rankin, John; Ratheesh, Ajay; Roberts, Oliver J.; Sgrò, Carmelo; Slane, Patrick; Soffitta, Paolo; Spandre, Gloria; Swartz, Douglas A.; Tamagawa, Toru; Taverna, Roberto; Tawara, Yuzuru; Thomas, Nicholas E.; Tombesi, Francesco; Trois, Alessio; Tsygankov, Sergey S.; Turolla, Roberto; Vink, Jacco; Weisskopf, Martin C.; Xie, Fei; Zane, Silvia
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Abstract
The magnetic field conditions in astrophysical relativistic jets can be probed by multiwavelength polarimetry, which has been recently extended to X-rays. For example, one can track how the magnetic field changes in the flow of the radiating particles by observing rotations of the electric vector position angle $\Psi$. Here we report the discovery of a $\Psi_{\mathrm x}$ rotation in the X-ray band in the blazar Mrk 421 at an average flux state. Across the 5 days of Imaging X-ray Polarimetry Explorer (IXPE) observations of 4-6 and 7-9 June 2022, $\Psi_{\mathrm x}$ rotated in total by $\geq360^\circ$. Over the two respective date ranges, we find constant, within uncertainties, rotation rates ($80 \pm 9$ and $91 \pm 8 ^\circ/\rm day$) and polarization degrees ($\Pi_{\mathrm x}=10\%\pm1\%$). Simulations of a random walk of the polarization vector indicate that it is unlikely that such rotation(s) are produced by a stochastic process. The X-ray emitting site does not completely overlap the radio/infrared/optical emission sites, as no similar rotation of $\Psi$ was observed in quasi-simultaneous data at longer wavelengths. We propose that the observed rotation was caused by a helical magnetic structure in the jet, illuminated in the X-rays by a localized shock propagating along this helix. The optically emitting region likely lies in a sheath surrounding an inner spine where the X-ray radiation is released.