Gamma-ray counterparts of 2WHSP high-synchrotron-peaked BL Lac objects as possible signatures of ultra-high-energy cosmic-ray emission

TL;DR

This study searches for gamma-ray emissions from high-synchrotron-peaked BL Lac objects to identify potential ultra-high-energy cosmic-ray sources, detecting 160 significant sources and proposing candidates for further TeV observations.

Contribution

It introduces a method to distinguish electromagnetic cascade emission from leptonic emission in high-redshift BL Lac objects using Fermi-LAT data, identifying promising UHECR candidate sources.

Findings

Detected 160 gamma-ray sources above 5σ significance.

Identified candidate sources for ultra-high-energy cosmic-ray emission.

Provided a prioritized list for follow-up TeV observations.

Abstract

We present a search for high-energy $\gamma$-ray emission from 566 Active Galactic Nuclei at redshift $z > 0.2$, from the 2WHSP catalog of high-synchrotron peaked BL Lac objects with eight years of Fermi-LAT data. We focus on a redshift range where electromagnetic cascade emission induced by ultra-high-energy cosmic rays can be distinguished from leptonic emission based on the spectral properties of the sources. Our analysis leads to the detection of 160 sources above $\approx$ $5\sigma$ (TS $\geq 25$) in the 1 - 300 GeV energy range. By discriminating significant sources based on their $\gamma$-ray fluxes, variability properties, and photon index in the Fermi-LAT energy range, and modeling the expected hadronic signal in the TeV regime, we select a list of promising sources as potential candidate ultra-high-energy cosmic-ray emitters for follow-up observations by Imaging Atmospheric Cherenkov Telescopes.