# The VHE anomaly in blazar spectra and related phenomena

## TL;DR

This paper reviews observed anomalies in very high energy gamma-ray spectra from blazars, discusses their potential explanations via electromagnetic cascades, and evaluates the viability of different models including hadronic cascades.

## Contribution

It provides a comprehensive review of VHE anomalies, discusses the cascade development explanations, and compares electromagnetic and hadronic cascade models.

## Key findings

- VHE anomalies are not supported by exotic interpretations.
- Intergalactic electromagnetic cascades naturally explain the anomalies.
- Hadronic cascade models require specific magnetic field conditions.

## Abstract

Most of the recent research on extragalactic $\gamma$-ray propagation focused on the study of the $\gamma\gamma \rightarrow e^{+}e^{-}$ absorption process ("absorption-only model"). Starting from a possible anomaly at very high energies (VHE, E >100 GeV), we briefly review several existing deviations from this model. The exotic interpretation of the VHE anomaly is not supported by the recent works. On the other hand, the process of intergalactic electromagnetic cascade development naturally explains these effects. We discuss phenomenology of intergalactic cascades and the main spectral signatures of the electromagnetic cascade model. We also briefly consider the hadronic cascade model; it also may explain the data, but requires low strength of magnetic field around the source of primary protons or nuclei.