# Cherenkov Telescope Array

The Cherenkov Telescope Array, or CTA, is a multinational, worldwide project to build a new generation of ground-based gamma-ray instruments in the energy range extending from some tens of GeV to about 300 TeV. It is proposed as an open observatory and will consist of two arrays of imaging atmospheric Cherenkov telescopes (IACT), a first array at the Northern Hemisphere with emphasis on the study of extragalactic objects at the lowest possible energies, and a second array at the Southern Hemisphere, which is to cover the full energy range and concentrate on galactic sources. The physics program of CTA goes beyond high-energy astrophysics into cosmology and fundamental physics.
Building on the technology of current-generation ground-based gamma-ray detectors (MAGIC, HESS, and VERITAS), CTA will be ten times more sensitive and have unprecedented accuracy in its detection of high-energy gamma rays. Current gamma-ray telescope arrays host up to five individual telescopes, but CTA is designed to detect gamma rays over a larger area and a wider range of views, with more than 100 telescopes located in the northern and southern hemispheres. At least three classes of telescopes are required to cover the full CTA energy range (20 GeV to 300 TeV): Large-Sized Telescope (LST), Medium-Sized Telescope (MST), and Small-Sized Telescope (SST).
The project to build CTA is well advanced: prototypes exist for all the proposed telescope designs, and significant site characterization and preparations are underway. An intergovernmental agreement for construction and subsequent operation of the observatory—a European Research Infrastructure Consortium (ERIC)—is in preparation, and the financial threshold is expected to be reached in 2019.
The project was promoted to a landmark on the roadmap of the European Strategy Forum on Research Infrastructures (ESFRI) and is on the roadmaps for the Aspera European Astroparticle network and Astronet. The cost for baseline design of the project is estimated at €300 million (US$350 million).

## Members

As of December 2018, the CTA consortium includes more than 1,420 members from 210 institutes in 31 countries: Armenia, Australia, Austria, Brazil, Bulgaria, Canada, Chile, Croatia, Czech Republic, Finland, France, Germany, Greece, India, Ireland, Italy, Japan, Mexico, Namibia, Netherlands, Norway, Poland, Slovenia, South Africa, Spain, Sweden, Switzerland, Thailand, the United Kingdom, Ukraine, and the United States.

## Array sites

On 15 and 16 July 2015, the CTA decided to enter into detailed contract negotiations for hosting CTA at the European Southern Observatory (ESO) of Paranal Observatory, in Chile, and at the Instituto de Astrofisica de Canarias (IAC), Roque de los Muchachos Observatory in La Palma, Spain. On 19 September 2016, the Council of the Cherenkov Telescope Array Observatory (CTAO) concluded negotiations with the IAC to host CTA's northern-hemisphere array. On 19 December 2018, final agreements were signed for the southern array as well.
CTA's northern hemisphere site is located on the existing site of the IAC's Roque de los Muchachos Observatory on the island of La Palma, the fifth largest island in the Canary Islands. At 2,200 metres of altitude and nestled on a plateau below the rim of an extinct volcanic crater, the site currently hosts an operating gamma-ray observatory, the Major Atmospheric Gamma Ray Imaging Cherenkov (MAGIC) telescopes, as well as a variety of optical telescopes of various sizes.

## Science

CTA will look at higher-energy photons than ever measured before. Its cosmic particle accelerators can reach energies inaccessible to such accelerators as the Large Hadron Collider. CTA will seek to understand the impact of high-energy particles in the evolution of cosmic systems and to gain insight into the most extreme and unusual phenomena in the Universe. It will also search for annihilating dark matter particles and deviations from Einstein's theory of special relativity, even conducting a census of particle acceleration in the Universe.
Research at the CTA will seek to address questions in and beyond astrophysics that fall under three major themes of study: understanding the origin and role of relativistic cosmic particles, probing extreme environments, and exploring frontiers in physics. To address these themes, CTA will observe the following key targets: Galactic Center, Large Magellanic Cloud, Galactic Plane, galaxy clusters, cosmic ray PeVatrons, star-forming systems, active galactic nuclei, and transient phenomena.