Target of Opportunity observations of blazars with H.E.S.S.$\ $

TL;DR

This paper discusses H.E.S.S.'s targeted observations of blazars, highlighting two major discoveries in 2015: VHE emission from 3C 279 and the identification of PKS 0736+017 as a new VHE quasar.

Contribution

It presents the status and results of H.E.S.S. blazar target of opportunity observations, including significant detections and discoveries in 2015.

Findings

Detection of VHE emission from 3C 279 during a flare

Discovery of PKS 0736+017 as a new VHE quasar

Approximately 70 hours of blazar ToO data collected in 2015

Abstract

The very high energy (VHE, E > 100 GeV) sky is dominated by blazars, radio-loud active galactic nuclei whose relativistic jet is closely aligned with the line of sight. Blazars are characterized by rapid variability at all wavelengths and thus an important part of the H.E.S.S. blazar program is devoted to target of opportunity (ToO) observations. H.E.S.S. triggers blazar ToOs on the basis of publicly available blazar observations at longer wavelengths (optical, X-rays, and $\gamma$-rays), from private optical observations with the ATOM telescope, and from private communications by $\gamma$-ray partners in the context of MoUs. In 2015, about 70 hours of H.E.S.S. data were taken in the form of blazar ToOs, which represents ~15$\%$ of all extragalactic observations. In this contribution, we present the H.E.S.S. blazar ToO status, and we focus on two major results from the 2015 season: the detection of VHE emission from 3C 279 during the June 2015 flare, and the discovery of PKS 0736+017 as a new VHE quasar.