Abstract
The High Energy Stereoscopic System (H.E.S.S.) is an array of five Imaging Atmospheric Cherenkov Telescopes located in the Khomas Highland in Namibia. It measures cosmic gamma-rays with very high energies (> 100 GeV) using the Earth's atmosphere as a calorimeter. The H.E.S.S. experiment has entered Phase II in September 2012 with the inauguration of a fifth telescope that is larger and more complex than the other four. The very large mirror area of 600 m2 in comparison to the 100 m2 of the smaller telescopes results in a lower energy threshold as well as an increased overall sensitivity of the system. Moreover, the huge effective area, due to the large mirror size, is crucial in the detection of short time scale low energy transient events. This paper will give a brief overview of the design principles of the current H.E.S.S. data acquisition and array control system. Particular emphasis is given to the new Target of Opportunity alert system that has recently been introduced to the array and allows the instrument to react to such an alert within 60 s.
Highlights
With the current generation of ground-based Imaging Atmospheric Cherenkov Telescopes (IACTs), the field of very high energy (VHE; > 100 GeV) gamma-ray astronomy has become an important part of Astroparticle Physics
The hierarchy of Managers, and, of Contexts, is as follows: at the top the so-called RunManager is responsible for monitoring available resources and starting scheduled runs ; the level below consists of the different SubArray-Managers which take care of all processes that belong to a subset of the array that should take data on a given target; come the Managers for specific tasks in the Data Acquisition System (DAQ) such as the control of all processes concerned with a particular telescope
Due to the unpredictable nature of Target of Opportunity (ToO) alerts, the DAQ must be able to react in any given state, regardless of one or multiple runs currently ongoing or of a SubArray currently being in transition
Summary
With the current generation of ground-based Imaging Atmospheric Cherenkov Telescopes (IACTs), the field of very high energy (VHE; > 100 GeV) gamma-ray astronomy has become an important part of Astroparticle Physics. The H.E.S.S. DAQ allows the array to operate in different observation modes with different sets of telescopes at the same time using so-called SubArrays. The hierarchy of Managers, and, of Contexts, is as follows: at the top the so-called RunManager is responsible for monitoring available resources and starting scheduled runs ; the level below consists of the different SubArray-Managers which take care of all processes that belong to a subset of the array that should take data on a given target; come the Managers for specific tasks in the DAQ such as the control of all processes concerned with a particular telescope.
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