Target of Opportunity observations of blazars with H.E.S.S.$\ $
  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. 
M. Cerruti, M. B\"ottcher, N. Chakraborty, I.D. Davids, M.   F\"u{\ss}ling, F. Jankowsky, J.P. Lenain, M. Meyer, H. Prokoph,...
astro-ph.HE