Dr. Markus Holler (Innsbruck, Austria)
" After the H.E.S.S. I Legacy - Challenges and Prospects for the First Hybrid IACT Array"
The High Energy Stereoscopic System (H.E.S.S.) is one of the major 3 experiments that turned ground-based gamma-ray astronomy with Imaging Atmospheric Cherenkov Telescopes (IACTs) from a small research field into an established branch of astrophysics. H.E.S.S. originally consisted of four identical IACTs (CT1-4) with an effective mirror diameter of 12 m which were operated in stereoscopic mode (H.E.S.S. I). In 2012, a 28 m telescope (CT5, the largest IACT in the world) was added, making it the first actual hybrid IACT array (H.E.S.S. II). The array is operated in hybrid mode, meaning that showers that trigger CT5 are always read out to lower the energy threshold and bridge the gap to Fermi-LAT; events that trigger CT1-4 are however only read out if at least two telescopes were triggered to ensure stereoscopic reconstruction, thus implying better angular and energy resolution. Combining telescopes of different size and configuration requires adaptations on many different levels to reach the desired science performance. In this presentation I will talk about the different challenges and current approaches to handle the data analysis of H.E.S.S. II with respect to its hybrid layout and operation mode. Such work is opening the way to the operation of hybrid arrays and will thus benefit future projects such as the Cherenkov Telescope Array (CTA).