High energy blazar physics in the Multi-Messenger context

Active galactic nuclei (AGN) are among the most powerful sources in the Universe, dominating the non-thermal energy output across nearly all electromagnetic bands. Understanding the mechanisms behind this emission, such as accretion onto supermassive black holes, particle acceleration, magnetic field generation, and shock formation in relativistic plasma, is essential for interpreting high-energy and multi-messenger observations. These processes can be best probed through coordinated studies combining very-high-energy and high-angular-resolution observations.

I will present recent results from polarization VLBI studies that trace jet formation, acceleration, and magnetic field structure in AGN on parsec scales. Our observations provide clear evidence for a net toroidal magnetic field in a current-carrying blazar jet. We also find that blazars viewed at extremely small angles to the line of sight can naturally resolve the long-standing «Doppler factor crisis,» reconciling the low apparent jet speeds from VLBI with the high Doppler factors inferred from very-high-energy observations.

Our results highlight the central role of relativistic beaming in shaping the gamma-ray and neutrino emission of blazars. This suggests that parent PeV-scale protons exhibit relativistic bulk motion and offers new constraints for models of their multi-messenger output.

Fecha y lugar: 19/01/2026 – 13:00 | Salón de Actos
Yuri Kovalev
Max Planck Institute for Radio Astronomy