V. Stamatescu

On the potential of the Cherenkov Telescope Array for the study of cosmic-ray diffusion in molecular clouds

Aims. Molecular clouds act as primary targets for cosmic-ray interactions and are expected to shine in γ-rays as a by-product of these interactions. Indeed, several detected γ-ray sources both in HE and VHE γ-rays (HE: 100 MeV 100 GeV) have been directly or indirectly associated with molecular clouds. Information on the local diffusion coefficient and the cosmic-ray population can be inferred from the observed γ-ray signals. In this work we explore the capability of the forthcoming Cherenkov Telescope Array observatory (CTA) to provide such measurements. Methods. We investigate the expected emission from clouds hosting an accelerator, surveying the parameter space for different modes of acceleration, age of the source, cloud density profile, and cosmic-ray diffusion coefficient. Results. We present some of the most interesting cases for CTA regarding this science topic. The simulated γ-ray fluxes depend strongly on the input parameters. In several cases, we find that it will be possible to constrain both the properties of the accelerator and the propagation mode of cosmic rays in the cloud from CTA data alone.

Performance studies of the CTA observatory

The Cherenkov Telescope Array (CTA), currently in the Preparatory Phase, will study gamma rays in the energy range from a few tens of GeV to >100 TeV with unprecedented sensitivity and angular resolution. In order to cover such a vast energy range, an array of three complementary telescope types is envisaged: a small number of Large Size Telescopes (LST, 23m-diameter dish) for the low-energy range (below 200 GeV), few tens of Medium Size Telescopes (MST,12mdish)forthe central energy range (100 GeV - 10 TeV) and alarge number of Small Size Telescopes (SST, 4-7m dish) for the high energy range (above 10 TeV). The optimization of the performance (sensitivity, angular and energy resolutions) of such a complex system requires intensive simulation activities. Some preliminary results in terms of off-axis performance, operation under moonlight conditions and high altitude performance are reported and discussed.

Towards an optimized design for the Cherenkov Telescope Array

The Cherenkov Telescope Array (CTA) is a future instrument for very-high-energy (VHE) gamma-ray astronomy that is expected to deliver an order of magnitude improvement in sensitivity over existing instruments. In order to meet the physics goals of CTA in a cost-effective way, Monte Carlo simulations of the telescope array are used in its design. Specifically, we simulate large arrays comprising numerous large-size, medium-size and small-size telescopes whose configuration parameters are chosen based on current technical design studies and understanding of the costs involved. Subset candidate arrays with various layout configurations are then selected and evaluated in terms of key performance parameters, such as the sensitivity. This is carried out using a number of data analysis methods, some of which were developed within the field and extended to CTA, while others were developed specifically for this purpose. We outline some key results from recent studies that illustrate our approach to the optimization of the CTA design.