arXiv · 2305.13898
X-ray Polarization of BL Lacertae in Outburst
Abstract
We report the first $> 99\%$ confidence detection of X-ray polarization in BL Lacertae. During a recent X-ray/$\gamma$-ray outburst, a 287 ksec observation (2022 November 27-30) was taken using the Imaging X-ray Polarimetry Explorer ({\it IXPE}), together with contemporaneous multiwavelength observations from the Neil Gehrels {\it Swift} observatory and {\it XMM-Newton} in soft X-rays (0.3--10~keV), {\it NuSTAR} in hard X-rays (3--70~keV), and optical polarization from the Calar Alto, and Perkins Telescope observatories. Our contemporaneous X-ray data suggest that the {\it IXPE} energy band is at the crossover between the low- and high-frequency blazar emission humps. The source displays significant variability during the observation, and we measure polarization in three separate time bins. Contemporaneous X-ray spectra allow us to determine the relative contribution from each emission hump. We find $>99\%$ confidence X-ray polarization $\Pi_{2-4{\rm keV}} = 21.7^{+5.6}_{-7.9}\%$ and electric vector polarization angle $\psi_{2-4{\rm keV}} = -28.7 \pm 8.7^{\circ}$ in the time bin with highest estimated synchrotron flux contribution. We discuss possible implications of our observations, including previous {\it IXPE} BL Lacertae pointings, tentatively concluding that synchrotron self-Compton emission dominates over hadronic emission processes during the observed epochs.
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Abel L. Peirson, Michela Negro, Ioannis Liodakis, Riccardo Middei, Dawoon E. Kim, Alan P. Marscher, Herman L. Marshall, Luigi Pacciani, Roger W. Romani, Kinwah Wu, Alessandro Di Marco, Niccolo Di Lalla, Nicola Omodei, Svetlana G. Jorstad, Ivan Agudo, Pouya M. Kouch, Elina Lindfors, Francisco Jose Aceituno, Maria I. Bernardos, Giacomo Bonnoli, Victor Casanova, Maya Garcia-Comas, Beatriz Agis-Gonzalez, Cesar Husillos, Alessandro Marchini, Alfredo Sota, Carolina Casadio, Juan Escudero, Ioannis Myserlis, Albrecht Sievers, Mark Gurwell, Ramprasad Rao, Ryo Imazawa, Mahito Sasada, Yasushi Fukazawa, Koji S. Kawabata, Makoto Uemura, Tsunefumi Mizuno, Tatsuya Nakaoka, Hiroshi Akitaya, Whee Yeon Cheong, Hyeon-Woo Jeong, Sincheol Kang, Sang-Hyun Kim, Sang-Sung Lee, Emmanouil Angelakis, Alexander Kraus, Nicolo Cibrario, Immacolata Donnarumma, Juri Poutanen, Fabrizio Tavecchio, Lucio A. Antonelli, Matteo Bachetti, Luca Baldini, Wayne H. Baumgartner, Ronaldo Bellazzini, Stefano Bianchi, Stephen D. Bongiorno, Raffaella Bonino, Alessandro Brez, Niccolo Bucciantini, Fiamma Capitanio, Simone Castellano, Elisabetta Cavazzuti, Chien-Ting Chen, Stefano Ciprini, Enrico Costa, Alessandra De Rosa, Ettore Del Monte, Laura Di Gesu, Victor Doroshenko, Michal Dovciak, Steven R. Ehlert, Teruaki Enoto, Yuri Evangelista, Sergio Fabiani, Riccardo Ferrazzoli, Javier A. Garcia, Shuichi Gunji, Kiyoshi Hayashida, Jeremy Heyl, Wataru Iwakiri, Philip Kaaret, Vladimir Karas, Takao Kitaguchi, Jeffery J. Kolodziejczak, Henric Krawczynski, Fabio La Monaca, Luca Latronico, Grzegorz Madejski, Simone Maldera, Alberto Manfreda, Frederic Marin, Andrea Marinucci, Francesco Massaro, Giorgio Matt, Ikuyuki Mitsuishi, Fabio Muleri, C. -Y. Ng, Stephen L. O'Dell. 2023-05-23. X-ray Polarization of BL Lacertae in Outburst. https://doi.org/10.3847/2041-8213%2Facd242
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