Cherenkov Telescope Array Consortium Research Articles

The Cherenkov Telescope Array production system proto-type for large-scale data processing and simulations

The Cherenkov Telescope Array (CTA) is the next-generation instrument in the very-high energy gamma ray astronomy domain. It will consist of tens of Cherenkov telescopes deployed in 2 arrays at La Palma (Spain) and Paranal (ESO, Chile) respectively. Currently under construction, CTA will start operations around 2023 for a duration of about 30 years. During operations CTA is expected to produce about 2 PB of raw data per year plus 5-20 PB of Monte Carlo data. The global data volume to be managed by the CTA archive, including all versions and copies, is of the order of 100 PB with a smooth growing profile. The associated processing needs are also very high, of the order of hundreds of millions of CPU HS06 hours per year. In order to optimize the instrument design and study its performances, during the preparatory phase (2010-2017) and the current construction phase, the CTA consortium has run massive Monte Carlo productions on the EGI grid infrastructure. In order to handle these productions and the future data processing, we have developed a production system based on the DIRAC framework. The current system is the result of several years of hardware infrastructure upgrades, software development and integration of different services like CVMFS and FTS. In this paper we present the current status of the CTA production system and its exploitation during the latest large-scale Monte Carlo campaigns.

Sensitivity of the Cherenkov Telescope Array to a dark matter signal from the Galactic centre

We provide an updated assessment of the power of the Cherenkov Telescope Array (CTA) to search for thermally produced dark matter at the TeV scale, via the associated gamma-ray signal from pair-annihilating dark matter particles in the region around the Galactic centre. We find that CTA will open a new window of discovery potential, significantly extending the range of robustly testable models given a standard cuspy profile of the dark matter density distribution. Importantly, even for a cored profile, the projected sensitivity of CTA will be sufficient to probe various well-motivated models of thermally produced dark matter at the TeV scale. This is due to CTA's unprecedented sensitivity, angular and energy resolutions, and the planned observational strategy. The survey of the inner Galaxy will cover a much larger region than corresponding previous observational campaigns with imaging atmospheric Cherenkov telescopes. CTA will map with unprecedented precision the large-scale diffuse emission in high-energy gamma rays, constituting a background for dark matter searches for which we adopt state-of-the-art models based on current data. Throughout our analysis, we use up-to-date event reconstruction Monte Carlo tools developed by the CTA consortium, and pay special attention to quantifying the level of instrumental systematic uncertainties, as well as background template systematic errors, required to probe thermally produced dark matter at these energies.

РЕЗУЛЬТАТИ ФОТОМЕТРИЧНОГО ОПТИЧНОГО МОНІТОРИНГУ ЧОТИРЬОХ АКТИВНИХ ЯДЕР ГАЛАКТИК У 2018–2019 РОКАХ

Active galactic nuclei (AGN) are a source of very high energies. Blazars are a subclass of active galactic nuclei that can be observed in the optical spectral range. The aim of the study is some BL Lacertae type blazars, which are characterized by a non-emission optical spectrum and exhibit brightness variations at all wavelengths. The results of systematical monitoring of selected objects from the CTA (Cherenkov Telescope Array) optical follow up list, started in January 2018 are presented. The observations are carried out with the AZT-8 (D = 70 cm, F = 2.8 m) telescope of the observation station Lisnyky of Taras Shevchenko National University of Kyiv. In 2018 the telescope AZT-8 was included in the list of supporting instruments in the CTA consortium. The AZT-8 equipped with the PL4710-1-BB-E2V CCD (1027×1048 pixels, 13×13 µm/pixel, scale is 0.95 “/pixel, field of view is 16.2 angular minutes) and broadband Johnson/Bessel UBVRI filters. For processing the software Maxim DL was used. During processing accounting of substrate (bias), dark current, flat-field were taken into account. The fluxes of energy from objects of research with the help of standard stars has been turned into visible stellar magnitudes. Light curves for four objects: 1ES 1011+496, PKS 1222+216, 1ES 1426+428, PKS 1510-089 were plotted. Variability of color indexes with time was investigated. In addition, we determined the variability amplitude and tested all these objects for Intraday Variations (IDV), Short (STV) and Long term variability (LTV) where it was possible. A short-term brightness change (STV) with an amplitude of 0.5 to 1 in all filters (UBVRI) of the Johnson/Bessel system for AGN 1ES 1011+496, PKS 1510-089 was determined. For objects 1ES 1426+428 and PKS 1222+216, the brightness variations do not exceed the total error (instrumental and methodical). The total error is ∆Σ ≈ 0.060.1 magnitude.

Astroclimatic Characterization of Vallecitos: A Candidate Site for the Cherenkov Telescope Array at San Pedro Mártir

We conducted an 18 month long study of the weather conditions of the Vallecitos, a proposed site in México to harbor the northern array of the Cherenkov Telescope Array (CTA). It is located in Sierra de San Pedro Mártir (SPM) a few kilometers away from Observatorio Astronómico Nacional. The study is based on data collected by the ATMOSCOPE, a multi-sensor instrument measuring the weather and sky conditions, which was commissioned and built by the CTA Consortium. Additionally, we compare the weather conditions of the optical observatory at SPM to the Vallecitos regarding temperature, humidity, and wind distributions. It appears that the excellent conditions at the optical observatory benefit from the presence of microclimate established in the Vallecitos.

The readout and control system of the mid-size telescope prototype of the Cherenkov Telescope Array

The Cherenkov Telescope Array (CTA) is one of the major ground-based astronomy projects being pursued and will be the largest facility for ground-based y-ray observations ever built. CTA will consist of two arrays: one in the Northern hemisphere composed of about 20 telescopes, and the other one in the Southern hemisphere composed of about 100 telescopes, both arrays containing telescopes of different type and size. A prototype for the Mid-Size Telescope (MST) with a diameter of 12 m has been installed in Berlin and is currently being commissioned. This prototype is composed of a mechanical structure, a drive system and mirror facets mounted with powered actuators to enable active control. Five Charge-Coupled Device (CCD) cameras, and a wide set of sensors allow the evaluation of the performance of the instrument. The design of the control software is following concepts and tools under evaluation within the CTA consortium in order to provide a realistic test-bed for the middleware: 1) The readout and control system for the MST prototype is implemented with the Atacama Large Millimeter/submillimeter Array (ALMA) Common Software (ACS) distributed control middleware; 2) the OPen Connectivity-Unified Architecture (OPC UA) is used for hardware access; 3) the document oriented MongoDB database is used for an efficient storage of CCD images, logging and alarm information: and 4) MySQL and MongoDB databases are used for archiving the slow control monitoring data and for storing the operation configuration parameters. In this contribution, the details of the implementation of the control system for the MST prototype telescope are described.

Introducing the CTA concept

The Cherenkov Telescope Array (CTA) is a new observatory for very high-energy (VHE) gamma rays. CTA has ambitions science goals, for which it is necessary to achieve full-sky coverage, to improve the sensitivity by about an order of magnitude, to span about four decades of energy, from a few tens of GeV to above 100TeV with enhanced angular and energy resolutions over existing VHE gamma-ray observatories. An international collaboration has formed with more than 1000 members from 27 countries in Europe, Asia, Africa and North and South America. In 2010 the CTA Consortium completed a Design Study and started a three-year Preparatory Phase which leads to production readiness of CTA in 2014. In this paper we introduce the science goals and the concept of CTA, and provide an overview of the project.

Evaluating the control software for CTA in a medium size telescope prototype

CTA (Cherenkov Telescope Array) is one of the largest ground-based astronomy projects being pursued and will be the largest facility for ground-based γ-ray observations ever built. CTA will consist of two arrays (one in the Northern hemisphere and one in the Southern hemisphere) composed of telescopes of several sizes. A prototype for the Medium Size Telescope (MST) of a diameter of 12 m will be installed in Berlin by the end of 2012. This MST prototype will be composed of the mechanical structure, drive system and mirror facets mounted with powered actuators to enable active control. Five Charge-Coupled Device (CCD) cameras and a weather station will allow the measurement of the performance of the instrument. The Atacama Large Millimeter/submillimeter Array (ALMA) Common Software (ACS) distributed control framework is currently being considered by the CTA consortium to serve as the array control middleware. In order to evaluate the ACS software, it has been decided to implement an ACS-based readout and control system for the MST prototype. The design of the control software is following the concepts and tools under evaluation within the CTA consortium, like the use of a Unified Modeling Language (UML) based code generation framework for ACS component modeling, and the use of OPen Connectivity-Unified Architecture (OPC UA) for hardware access. In this contribution, the progress in the implementation of the control system for this CTA prototype telescope is described.

New Electronics for the Cherenkov Telescope Array

Very high energy gamma-ray astronomy is now bringing an invaluable contribution to the understanding of violent phenomena in the Universe, as well as the search for exotic physics such as indirect detection of dark matter or a test of Lorentz invariance violation. The current Imaging Arrays of Cherenkov Telescopes (IACT) show that this technique is mature. In Europe, the community is gathering around the Cherenkov Telescope Array consortium, to design and build the next generation ground-based array. It should reach an order of magnitude in sensitivity in a wide energy band, ranging from 10 GeV to more than 100 TeV. This goal can be achieved with an array of 50–100 telescopes of various sizes at various spacings. With about 2000 channels per camera, a specific effort has to be made to design front-end electronics with a lower cost and better performances. A gain in cost and performances can be obtained by maximising the integration of the front-end electronics in an ASIC. The amplifiers, analogue memories, digitization and first level buffering can be embedded in the same component. We present here the NECTAr project aiming at building a demonstrator element of a generic camera built around this component.