E. Lorenz

Long term VHE gamma ray monitoring of bright blazars with a dedicated Cherenkov telescope

We intend to set up an imaging air Cherenkov telescope with low cost, but high performance design for remote operation. The goal is to dedicate this gamma-ray telescope to long-term monitoring observations of nearby, bright blazars at very high energies (VHE). We will (i) search for orbital modulation of the blazar emission due to supermassive black hole binaries, (ii) study the statistics of flares and their physical origin, and (iii) correlate the data with observations of flares with higher sensitivity telescopes such as MAGIC, VERITAS, and H.E.S.S. Common observations with theWhipple 10m-monitoring telescope will be the first step towards a future 24 h-monitoring of selected sources. This idea was presented for the first time in [1]. The telescope design is based on a full technological upgrade of one of the former telescopes of the HEGRA collaboration, still located at the Observatorio del Roque de los Muchachos on the Canarian Island of La Palma (Spain). After this upgrade, the telescope will be operated robotic, its sensitivity will greatly be improved and a much lower energy threshold below 350GeV will be achieved.

Geiger-mode avalanche photodiodes as photodetectors in Cherenkov astronomy

The progress in the development of Geiger-mode avalanche photodiodes (G-APD) has resulted in devices which show great promise for Imaging Atmospheric Cherenkov Telescopes (IACT). In the course of the First G-APD Camera Test (FACT) project with the purpose to construct a G-APD based camera, their characteristics are analysed and measured in detail. The angle dependence of the photon detection efficiency was measured and found to be flat. The effects of saturation and cross-talk on the reconstruction of the number of detected photons was studied. Since these effects are of a statistical nature, the reconstructed number is limited in its precision. For small numbers of photons, crosstalk is the limiting factor. For photon numbers comparable to or higher than the number of cells of the G-APD, the main limitation is the saturation.

Light Sensor Candidates for the Cherenkov Telescope Array

We report on the characterization of candidate light sensors for use in the next-generation Imaging Atmospheric Cherenkov Telescope project called Cherenkov Telescope Array, a major astro-particle physics project of about 100 telescopes that is currently in the prototyping phase. Our goal is to develop with the manufacturers the best possible light sensors (highest photon detection efficiency, lowest crosstalk and afterpulsing). The cameras of those telescopes will be based on classical super-bi-alkali Photomultiplier tubes but also Silicon Photomultipliers are candidate light sensors. A full characterisation of selected sensors was done. We are working in close contact with several manufacturers, giving them feedback and suggesting improvements.

Cherenkov light based measurement of extensive air showers around the knee with the HEGRA experiment

Data of the wide angle atmospheric Cherenkov light detector array AIROBICC and the scintillator matrix of the HEGRA air shower detector complex are combined to determine the energy spectrum and coarse composition of charged cosmic rays in the energy interval from 300 TeV to 10 PeV.