# Fermi-LAT high $z$ AGN and the Extragalactic Background Light

## TL;DR

This paper investigates how the extragalactic background light affects the spectra of high-redshift gamma-ray sources observed by Fermi-LAT, using spectral fitting and Monte Carlo simulations to test EBL models and predict future observations with CTA.

## Contribution

It introduces a method to estimate the intrinsic spectra of high-z AGN and tests EBL models against VHE observations, enhancing understanding of the EBL's impact on gamma-ray astronomy.

## Key findings

- VHE photons from distant sources are consistent with current EBL models.
- Spectral fitting below 10 GeV can estimate unabsorbed source spectra.
- Upcoming CTA observations will improve EBL constraints.

## Abstract

Observations of distant gamma-ray sources are hindered by the presence of the extragalactic background light (EBL). In order to understand the physical processes that result in the observed spectrum of sources, it is imperative that a good understanding of the EBL is included. In this work, an investigation into the imprint of the EBL on the observed spectra of high redshift Fermi-LAT AGN is presented. By fitting the spectrum below $\sim$10 GeV, an estimation of the un-absorbed intrinsic source spectrum is obtained; by applying this spectrum to data up to 300 GeV, it is then possible to derive a scaling factor for different EBL models. A second approach uses 5 sources (PKS 0426-380, 4C +55.17, Ton 116, PG 1246+586 and RBS 1432) which were found to exhibit very high energy emission ($E_{\gamma}>100$ GeV). Through Monte Carlo simulations it is shown that the observation of VHE photons, despite the large distances of these objects, is consistent with current EBL models. Many of these sources would be observable with the upcoming ground based observatory the Cherenkov Telescope Array (CTA), leading to a better understanding of the EBL.