# Variability Study of Extreme Blazars with VERITAS

## TL;DR

This study analyzes long-term and short-term variability of extreme blazars observed by VERITAS, exploring correlations across energy bands and potential secondary gamma-ray production mechanisms.

## Contribution

It provides the first detailed variability analysis of extreme HBLs over multiple years, including energy-dependent variability and cosmic-ray interaction implications.

## Key findings

- Detected 39 VHE AGNs, including 24 HBLs and xHBLs.
- Characterized long-term variability over 11 years.
- Explored energy-dependent short-term variability and secondary gamma-ray production.

## Abstract

The VERITAS array of imaging atmospheric Cherenkov telescopes has collected nearly 6000 hours of observations of active galactic nuclei (AGNs). It has detected 39 very-high-energy (VHE, >100 GeV) AGNs at redshifts up to z = 0.9, of which 24 are classified as high-frequency-peaked BL Lacertae objects (HBLs). VERITAS has obtained an extensive dataset of HBL, including extreme HBL (xHBL), observations, with lightcurves spanning up to 11 years, allowing the characterization of their long-term and short-term variability. A study of various xHBLs/HBLs in the VERITAS dataset is presented, and the correlation with other energy bands tested. In particular, the short-term variability of xHBLs as a function of energy within the VHE band is examined, exploring the possibility that secondary gamma rays are produced in cosmic-ray interactions with background photons.