Long-term multiwavelength view and modeling of the blazar B2 1811+31 in high state

Intermediate synchrotron-peaked BL Lacs (IBLs) are quite rare sources in the very high-energy (VHE; $100\,\rm GeV < E < 100\,\rm TeV$) $\gamma$-ray sky. The IBL B2 1811+31 ($z = 0.117$) showed intense flaring activity in 2020. This event was detected by a wide range of multiwavelength instruments from radio up to $\gamma$ rays. The observations carried out by the MAGIC telescopes led to the first-time detection of VHE $\gamma$-ray emission from B2 1811+31. In this contribution, we highlight the key results of our recent study \cite{Abe2025}, which offers a comprehensive analysis of the source emission both during the 2020 high-activity state and during the quiescent state. Using a comprehensive dataset, we contextualize this high-state episode within the source emissions over 18 years, from 2005 to 2024. We attribute the VHE $\gamma$-ray emission and the spectral and variability properties in the X-ray band to the electrons and positrons accelerated at the highest energies in the jet of the source. We propose a leptonic two-zone self-consistent model to interpret the observed multiwavelength emission during the 2020 flaring state. In the proposed scenario, the particle distributions in the two emission zones are steady-state solutions of the particle kinetic equation under the effects of injection of a power law spectrum of electrons and positrons, radiative losses and particle escape from the emission regions.