Blazars at Very High Energies: Emission Modelling

TL;DR

This paper reviews the current models of blazar emission at very high energies, highlighting their successes and challenges in explaining observed spectra, flaring activity, and extreme sources, and emphasizes the need for multi-wavelength studies to clarify underlying mechanisms.

Contribution

It provides a comprehensive overview of leptonic and lepto-hadronic models for blazar VHE emission, discussing their limitations and the importance of multi-messenger approaches for understanding particle acceleration and emission zones.

Findings

Current models explain spectra but struggle with flares and extreme sources.

Multi-wavelength and multi-messenger data are crucial for resolving model degeneracies.

Understanding particle acceleration and emission zones is key to advancing blazar physics.

Abstract

Blazars are very broadband cosmic sources with spectra spanning over twenty orders of magnitude in frequency, down to the 100 MHz regime in the radio range, up to VHE at several tens of TeV. The modelling of their spectral energy distribution at high energies currently considers two main classes of models, leptonic and lepto-hadronic, which both succeed fairly well in describing the observed spectra for the two populations of blazars, namely BL Lac objects (BL Lacs) and flat spectrum radio quasars (FSRQs). However they are both confronted with difficulties, in particular to reproduce flaring phenomena monitored with a good multi-spectral and temporal coverage, or to reproduce extreme sources which challenge the basic descriptions. Such a situation has led to a diversity of specific scenarios, the positioning of which in relation to the general context of the sources is generally not clearly fixed. The identification of the dominant particle acceleration mechanism at work and a better understanding of the location of the TeV emitting zone would make it possible to break the degeneracies between models. Multi-wavelength and multi-messenger studies should also help in this regard, with the perspective to elaborate a general reference scenario of blazars and AGNs.