# Observations of blazar PKS 2023-07 in flaring state with HESS and Fermi-LAT in 2016-2017 and constraints on an intrinsic cut-off

## TL;DR

This study reports on multi-wavelength observations of the distant blazar PKS 2023-07 during flaring states, providing constraints on its gamma-ray spectrum and intrinsic cutoff, despite non-detections at very high energies.

## Contribution

It presents the first combined analysis of H.E.S.S. and Fermi-LAT data for PKS 2023-07, setting new limits on its intrinsic gamma-ray spectral cutoff.

## Key findings

- No significant H.E.S.S. detection; upper limits established.
- Constraints on the intrinsic gamma-ray cutoff energy.
- Multi-wavelength observations during flares enhance understanding of distant blazar spectra.

## Abstract

PKS 2023-07 is a flat spectrum radio quasar located at a redshift $z=1.388$, farther than any source currently detected at very high energies ($E>100$ GeV). At such energies, absorption by the extragalactic background light (EBL) renders the detection of distant sources particularly challenging. The High Energy Stereoscopic System (H.E.S.S.) observed the source following reports from AGILE (April 2016) and Fermi-LAT (April 2016, September and October 2017) on high-flux states in gamma rays. During each of the three flaring periods, near-simultaneous observations were obtained with H.E.S.S., Fermi-LAT and multiple telescopes at other wavelengths. Though the source was not significantly detected by H.E.S.S., upper limits were derived for each observation period. Through constraints given by Fermi-LAT in the MeV--GeV domain and differential upper limits by H.E.S.S., we searched for an intrinsic cutoff in the EBL-corrected gamma ray spectrum of PKS 2023-07.