# H.E.S.S. observations of the flaring gravitationally lensed galaxy PKS 1830-211

## TL;DR

This paper reports on H.E.S.S. observations of the gravitationally lensed quasar PKS 1830-211 following a Fermi-LAT detected flare, but finds no significant gamma-ray signal above 67 GeV, setting upper limits on its flux.

## Contribution

First H.E.S.S. observations of PKS 1830-211 after a Fermi-LAT flare, providing constraints on very-high-energy gamma-ray emission from a lensed quasar.

## Key findings

- No significant gamma-ray excess detected by H.E.S.S.
- Established upper limits on PKS 1830-211 flux above 67 GeV.
- Compared H.E.S.S. upper limits with Fermi-LAT flare spectrum extrapolation.

## Abstract

PKS 1830-211 is a known macrolensed quasar located at a redshift of z=2.5. Its high-energy gamma-ray emission has been detected with the Fermi-LAT instrument and evidence for lensing was obtained by several authors from its high-energy data. Observations of PKS 1830-211 were taken with the H.E.S.S. array of Imaging Atmospheric Cherenkov Telescopes in August 2014, following a flare alert by the Fermi- LAT collaboration. The H.E.S.S observations were aimed at detecting a gamma-ray flare delayed by 20-27 days from the alert flare, as expected from observations at other wavelengths. More than twelve hours of good quality data were taken with an analysis threshold of $\sim67$ GeV. The significance of a potential signal is computed as a function of the date as well as the average significance over the whole period. Data are compared to simultaneous observations by Fermi-LAT. No photon excess or significant signal is detected. An upper limit on PKS 1830-211 flux above 67 GeV is computed and compared to the extrapolation of the Fermi-LAT flare spectrum.