Target of Opportunity Observations of Blazars with H.E.S.S

TL;DR

This paper discusses H.E.S.S.'s targeted follow-up observations of blazars during flaring events at other wavelengths, detailing procedures and recent notable observations to understand their VHE emission variability.

Contribution

It presents the H.E.S.S. extragalactic ToO program, outlining procedures for multi-wavelength alert follow-ups and showcasing recent significant blazar observations.

Findings

Successful detection of VHE emission during blazar flares

Enhanced understanding of blazar variability at VHE

Effective multi-wavelength alert follow-up procedures

Abstract

The very-high-energy (VHE, E>100 GeV) extragalactic sky is dominated by blazars, a class of active galactic nuclei which show rapid variability at all wavelengths. Target of Opportunity (ToO) observations triggered by flaring activity detected at longer wavelengths are, thus, an important part of the blazar observing strategy of H.E.S.S., an array of five imaging atmospheric Cherenkov telescopes sensitive to VHE photons. In this contribution we detail the H.E.S.S. extragalactic ToO program, describing the specific procedures currently in place to follow up on multi-wavelength alerts. The program is illustrated by discussing a few recent noteworthy targets observed with the H.E.S.S. phase II array over the last two years of blazar ToO observations.