mode with the Cherenkov Telescope Array
CTA is a ground-based observatory for gamma-ray astronomy at very high energies in the range of 20 GeV ÷ 300 TeV, and it will be the biggest observatory constructed so far with more than 100 telescopes in two different sites, one in the northern emisphere and the other in the southern.
The detection of gamma-rays is based on the imaging air Cherenkov technique. CTA is composed by three classes of telescopes: Large Sized Telescope (LST), aimed at covering the energy range 20 GeV ÷ 100 GeV, Middle Sized Telescope (MST), covering the core range 100 GeV ÷ 10 TeV and the more sensitive Small Sized Telescopes (SST) that will expand the energy range of the array up to 300 TeV. For CTA, major objectives should be an improved Galactic and Extragalactic plane survey for the southern site and the capacity of performing an all-sky survey in unprecedentedly short time at high sensitivity for the northern site.
The main idea of the project is to investigate sky survey performed in normal and divergent mode. The optimization of the pointing strategy, taking into account numerous characteristics of an array, such as distance between telescopes, field of view (FOV), energy threshold etc, can significantly reduce the observation time needed to achieve a given sensitivity. In the normal approach, sky surveys may be performed with telescopes pointed parallelly into the same direction of the sky, however, in such a case the FOV of the telescope system is highly limited by the FOVs of individual telescopes and the time needed for the scan is large. The FOV of a telescope array can be significantly enlarged by slightly deviating the pointing direction of each telescope: in the divergent mode, telescopes are inclined into the outward direction by an angle increasing with the telescope distance from the array center.
This pointing mode leads to an increase of the array FOV up to ∼ 14° or even larger. The goal is the study of the performance of the divergent mode for different array configurations and number of telescopes, and see if the performance are competitive compared to normal pointing. This type of observation should also improve CTA capacity to detect transient event, like Gamma Ray Bursts, thanks to LSTs fast repointing capability and low energy threshold.