X-Ray Polarization of BL Lacertae in Outburst

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 , Niccoló Di Lalla , Nicola Omodei , Svetlana G. Jorstad , Iván Agudo , Pouya M. Kouch , Elina Lindfors , Francisco José Aceituno , Maria I. Bernardos , Giacomo Bonnoli , Víctor Casanova , Maya García-Comas , Beatriz Agís-González , César 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 , Yeon Cheong , Hyeon-Woo Jeong , Sincheol Kang , Sang-Hyun Kim , Sang-Sung Lee , Emmanouil Angelakis , Alexander Kraus , Nicoló 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 , Niccoló 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 Dovčiak , 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 , Frédéric Marin (1) , Andrea Marinucci , Francesco Massaro , Giorgio Matt , Ikuyuki Mitsuishi , Fabio Muleri , C. -Y. Ng , Stephen L. O'Dell , Chiara Oppedisano , Alessandro Papitto , George G. Pavlov , Matteo Perri , Melissa Pesce-Rollins , Pierre-Olivier Petrucci (2) , Maura Pilia , Andrea Possenti , Simonetta Puccetti , Brian D. Ramsey , John Rankin , Ajay Ratheesh , Oliver J. Roberts , Carmelo Sgró , Patrick Slane , Paolo Soffitta , Gloria Spandre , Douglas A. Swartz , Toru Tamagawa , Roberto Taverna , Yuzuru Tawara , Allyn F. Tennant , Nicholas E. Thomas , Francesco Tombesi , Alessio Trois , Sergey Tsygankov , Roberto Turolla , Jacco Vink , Martin C. Weisskopf , Fei Xie , Silvia Zane

1 ObAS - Observatoire astronomique de Strasbourg
2 IPAG - Institut de Planétologie et d'Astrophysique de Grenoble

We report the first >99% confidence detection of X-ray polarization in BL Lacertae. During a recent X-ray/γ-ray outburst, a 287 ks observation (2022 November 27-30) was taken using the Imaging X-ray Polarimetry Explorer (IXPE), together with contemporaneous multiwavelength observations from the Neil Gehrels Swift observatory and XMM-Newton in soft X-rays (0.3-10 keV), 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 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 ${{\rm{\Pi }}}_{2\mbox{--}4\mathrm{keV}}={21.7}_{-7.9}^{+5.6} \% $ and electric vector polarization angle ψ _2-4keV = -28.°7 ± 8.°7 in the time bin with highest estimated synchrotron flux contribution. We discuss possible implications of our observations, including previous IXPE BL Lacertae pointings, tentatively concluding that synchrotron self-Compton emission dominates over hadronic emission processes during the observed epochs.

Keywords: 1390; 289; 1810; Astrophysical black holes; Black hole physics; Supermassive black holes; Active galactic nuclei; Active galaxies; Jets; Galaxy jets; Relativistic jets; Compact radiation sources; X-ray astronomy

Domains: Sciences of the Universe [physics]

Abel L. Peirson, Michela Negro, Ioannis Liodakis, Riccardo Middei, Dawoon E. Kim, et al.. X-Ray Polarization of BL Lacertae in Outburst. The Astrophysical Journal Letters, 2023, 948, ⟨10.3847/2041-8213/acd242⟩. ⟨insu-04102297⟩