Overview

• NASA's IXPE, in collaboration with ground-based telescopes, identified Compton scattering by electrons as the source of X-ray emissions in the blazar BL Lacertae's jets.
• The study utilized polarization measurements, finding X-ray polarization capped at 7.6% compared to a record-high optical polarization of 47.5%.
• This discovery resolves a longstanding debate between electron-photon interactions and proton-driven mechanisms in jet physics.
• The observations were conducted during a seven-day campaign in November 2023, combining IXPE data with simultaneous optical and radio measurements.
• The results, led by Iván Agudo and team, are now available as an arXiv preprint and will be published in the Astrophysical Journal Letters.