Letter to the Editor

Determining the origin of the X-ray emission in blazars through multiwavelength polarization

¹ Institute of Astrophysics, Foundation for Research and Technology-Hellas, GR-70013 Heraklion, Greece
² Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany
³ NASA Marshall Space Flight Center, Huntsville, AL 35812, USA
⁴ University of Maryland Baltimore County Baltimore, Baltimore, MD 21250, USA
⁵ NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
⁶ INAF Osservatorio Astronomico di Brera, Via E. Bianchi 46, 23807 Merate, (LC), Italy
⁷ Space Science Data Center, Agenzia Spaziale Italiana, Via del Politecnico snc, 00133 Roma, Italy
⁸ INAF Osservatorio Astronomico di Roma, Via Frascati 33, 00078 Monte Porzio Catone (RM), Italy
⁹ Instituto de Astrofísica de Andalucía, IAA-CSIC, Glorieta de la Astronomía s/n, 18008 Granada, Spain
¹⁰ Istituto Nazionale di Fisica Nucleare, Sezione di Padova, 35131 Padova, Italy
¹¹ Department of Physics, University of Crete, GR-70013 Heraklion, Greece
¹² Centre for Space Research North-West University Potchefstroom, Potchefstroom 2531, South Africa
¹³ Science and Technology Institute, Universities Space Research Association, Huntsville, AL 35805, USA
¹⁴ Institute for Astrophysical Research, Boston University, 725 Commonwealth Avenue, Boston, MA 02215, USA
¹⁵ St. Petersburg State University, 7/9, Universitetskaya nab., 199034 St. Petersburg, Russia
¹⁶ Physics Department and McDonnell Center for the Space Sciences, Washington University in St. Louis, St. Louis, MO 63130, USA
¹⁷ Department of Physics and Kavli Institute for Particle Astrophysics and Cosmology, Stanford University, Stanford, California 94305, USA
¹⁸ Department of Physics and Astronomy, University of Turku, Turku FI-20014, Finland
¹⁹ Finnish Centre for Astronomy with ESO (FINCA), Quantum, Vesilinnantie 5, FI-20014 University of Turku, Finland
²⁰ Aalto University Metsähovi Radio Observatory, Metsähovintie 114, FI-02540 Kylmälä, Finland
²¹ Astrophysics Research Institute, Liverpool John Moores University, Liverpool Science Park IC2, Liverpool, 146 Brownlow Hill, UK
²² Institut de Radioastronomie Millimétrique, Avenida Divina Pastora, 7, Local 20, E-18012 Granada, Spain
²³ Center for Astrophysics | Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138, USA
²⁴ Korea Astronomy and Space Science Institute, 776 Daedeok-daero, Yuseong-gu, Daejeon 34055, Korea
²⁵ University of Science and Technology, Korea, 217 Gajeong-ro, Yuseong-gu, Daejeon 34113, Korea
²⁶ Section of Astrophysics, Astronomy & Mechanics, Department of Physics, National and Kapodistrian University of Athens, Panepistimiopolis, Zografos 15784, Greece
²⁷ Institute of Astronomy and NAO, Bulgarian Academy of Sciences, 1784 Sofia, Bulgaria
²⁸ Pulkovo Observatory, St.Petersburg 196140, Russia

^⋆ Corresponding author: liodakis@ia.forth.gr

Received: 25 March 2025
Accepted: 13 May 2025

Abstract

The origin of the high-energy emission in astrophysical jets from black holes is a highly debated issue. This is particularly true for jets from supermassive black holes, which are among the most powerful particle accelerators in the Universe. So far, the addition of new observations and new messengers have only managed to create more questions than answers. However, the newly available X-ray polarization observations promise to finally distinguish between emission models. We use extensive multiwavelength and polarization campaigns as well as state-of-the-art polarized spectral energy distribution models to attack this problem by focusing on two X-ray polarization observations of blazar BL Lacertae in flaring and quiescent γ-ray states. We find that, regardless of the jet composition and underlying emission model, inverse-Compton scattering from relativistic electrons dominates at X-ray energies.