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Anisotropy test of the axion-like particle Universe opacity effect: a case for the Cherenkov Telescope Array  [PDF]
D. Wouters,P. Brun
Physics , 2013, DOI: 10.1088/1475-7516/2014/01/016
Abstract: The Universe opacity to gamma rays is still an open question, in particular anomalies may have been observed. Assuming that such anomalies find their origin in conventional physics like intrinsic source spectra or the density of the extragalactic background light, they would be evenly distributed over the sky. If they exist, axion-like particles (ALPs) would have a potential effect on the opacity of the Universe to gamma rays, possibly related to the anomalies in the spectral indices of distant gamma-ray sources. In the scenario where ALPs from distant sources convert back to photons in the Galactic magnetic field, their effect on the opacity is expected to depend on the position of the sources. In that case the anomaly is expected to exhibit peculiar correlations on the sky. We propose a method to test the origin of the opacity anomaly, based on angular correlations of spectral softening anomalies. Such a diagnosis requires a wide-field survey of high-energy gamma-ray sources over a broad range of energy. The future Cherenkov Telescope Array (CTA) is perfectly suited to perform such a study. It is shown that while the current sample of sources is not large enough to base conclusions on, with this method CTA will be sensitive to ALP couplings to gamma rays of the order of 3e-11 GeV^-1 for ALP masses below 1e-8 eV.
Calibration of the Cherenkov Telescope Array  [PDF]
Markus Gaug,Michael Daniel,David Berge,Raquel de los Reyes,Michele Doro,Andreas Foerster,Maria Concetta Maccarone,Dan Parsons,Christopher van Eldik,for the CTA Consortium
Physics , 2015,
Abstract: The construction of the Cherenkov Telescope Array is expected to start soon. We will present the baseline methods and their extensions currently foreseen to calibrate the observatory. These are bound to achieve the strong requirements on allowed systematic uncertainties for the reconstructed gamma-ray energy and flux scales, as well as on the pointing resolution, and on the overall duty cycle of the observatory. Onsite calibration activities are designed to include a robust and efficient calibration of the telescope cameras, and various methods and instruments to achieve calibration of the overall optical throughput of each telescope, leading to both inter-telescope calibration and an absolute calibration of the entire observatory. One important aspect of the onsite calibration is a correct understanding of the atmosphere above the telescopes, which constitutes the calorimeter of this detection technique. It is planned to be constantly monitored with state-of-the-art instruments to obtain a full molecular and aerosol profile up to the stratosphere. In order to guarantee the best use of the observation time, in terms of usable data, an intelligent scheduling system is required, which gives preference to those sources and observation programs that can cope with the given atmospheric conditions, especially if the sky is partially covered by clouds, or slightly contaminated by dust. Ceilometers in combination with all-sky-cameras are plannned to provide the observatory with a fast, online and full-sky knowledge of the expected conditions for each pointing direction. For a precise characterization of the adopted observing direction, wide-field optical telescopes and Raman Lidars are planned to provide information about the height-resolved and wavelength-dependent atmospheric extinction, throughout the field-of-view of the cameras.
The hunt for axionlike particles with the Cherenkov Telescope Array  [PDF]
Miguel A. Sanchez-Conde,Stefan Funk,Frank Krennrich,Amanda Weinstein
Physics , 2013,
Abstract: Gamma-ray photons can convert into axion-like particles (ALPs) and vice versa when interacting with astrophysical magnetic fields. The conversions of ALPs may have important implications for astrophysics since they would imprint characteristic features on the spectra of gamma-ray sources. The features may be detected by the Fermi Gamma-ray Space Telescope and by current Imaging Atmospheric Cherenkov Telescopes (IACTs) or the future Cherenkov Telescope Array (CTA). Thus, gamma-ray observations can provide valuable constraints on the nature of ALPs, and represent an excellent complementary approach to laboratory searches for ALPs. CTA's twenty times larger collection area and improved sensitivity compared to current IACTs will make it an extraordinarily powerful instrument to search for signatures of ALPs imprinted in the spectra of gamma-ray sources in the energy range between a few tens of GeV up to a few dozen TeV. The US contribution of Medium Size Telescopes will be therefore particularly important for ALP searches, as it will improve the sensitivity of the core energy regime (100 GeV - 10 TeV) of CTA by a factor of 2-3. As photon/ALP conversions are used as the main vehicle in the search, rather than the usual self-annihilations for WIMP candidates, the unknown dark matter nature will be scrutinized from a different perspective. Indeed, CTA could probe a region of the ALP parameter space in which ALPs might account for the total cold dark matter content in the Universe.
Pulsar Prospects for the Cherenkov Telescope Array  [PDF]
T. Hassan,S. Bonnefoy,M. Lopez,N. Mirabal,J. A. Barrio,J. L. Contreras,R. de los Reyes,E. O. Wilhelmi,B. Rudak,for the CTA Consortium
Physics , 2012, DOI: 10.1063/1.4772379
Abstract: In the last few years, the Fermi-LAT telescope has discovered over a 100 pulsars at energies above 100 MeV, increasing the number of known gamma-ray pulsars by an order of magnitude. In parallel, imaging Cherenkov telescopes, such as MAGIC and VERITAS, have detected for the first time VHE pulsed gamma-rays from the Crab pulsar. Such detections have revealed that the Crab VHE spectrum follows a power-law up to at least 400 GeV, challenging most theoretical models, and opening wide possibilities of detecting more pulsars from the ground with the future Cherenkov Telescope Array (CTA). In this contribution, we study the capabilities of CTA for detecting Fermi pulsars. For this, we extrapolate their spectra with "Crab-like" power-law tails in the VHE range, as suggested by the latest MAGIC and VERITAS results.
Upgrade of the VERITAS Cherenkov Telescope Array  [PDF]
A. Nepomuk Otte,for the VERITAS collaboration
Physics , 2009,
Abstract: The VERITAS Cherenkov telescope array has been fully operational since Fall 2007 and has fulfilled or outperformed its design specifications. We are preparing an upgrade program with the goal to lower the energy threshold and improve the sensitivity of VERITAS at all accessible energies. In the baseline program of the upgrade we will relocate one of the four telescopes, replace the photo-sensors by higher efficiency photomultipliers and install a new trigger system. In the enhanced program of the upgrade we foresee, in addition, the construction of a fifth telescope and installation of an active mirror alignment system.
Schwarzschild-Couder Telescope for the Cherenkov Telescope Array  [PDF]
Kevin J. Meagher
Physics , 2014, DOI: 10.1117/12.2054979
Abstract: The Cherenkov Telescope Array (CTA) is the next major ground-based observatory for gamma-ray astronomy. With CTA gamma-ray sources will be studied in the very-high energy gamma-ray range of a few tens of GeV to 100 TeV with up to ten times better sensitivity than available with current generation instruments. We discuss the proposed US contribution to CTA that comprises imaging atmospheric Cherenkov telescope with Schwarzschild-Couder (SC) optics. Key features of the SC telescope are a wide field of view of eight degrees, a finely pixelated camera with silicon photomultipliers as photon detectors, and a compact and power efficient 1 GS/s readout. The progress in both the optical system and camera development are discussed in this paper.
Dark Matter and Fundamental Physics with the Cherenkov Telescope Array  [PDF]
M. Doro,J. Conrad,D. Emmanoulopoulos,M. A. Sanchez-Conde,J. A. Barrio,E. Birsin,J. Bolmont,P. Brun,S. Colafrancesco,S. H. Connell,J. L. Contreras,M. K. Daniel,M. Fornasa,M. Gaug,J. F. Glicenstein,A. Gonzalez-Munoz,T. Hassan,D. Horns,A. Jacholkowska,C. Jahn,R. Mazini,N. Mirabal,A. Moralejo,E. Moulin,D. Nieto,J. Ripken,H. Sandaker,U. Schwanke,G. Spengler,A. Stamerra,A. Viana,H. S. Zechlin,S. Zimmer,for the CTA collaboration
Physics , 2012, DOI: 10.1016/j.astropartphys.2012.08.002
Abstract: The Cherenkov Telescope Array (CTA) is a project for a next-generation observatory for very high energy (GeV-TeV) ground-based gamma-ray astronomy, currently in its design phase, and foreseen to be operative a few years from now. Several tens of telescopes of 2-3 different sizes, distributed over a large area, will allow for a sensitivity about a factor 10 better than current instruments such as H.E.S.S, MAGIC and VERITAS, an energy coverage from a few tens of GeV to several tens of TeV, and a field of view of up to 10 deg. In the following study, we investigate the prospects for CTA to study several science questions that influence our current knowledge of fundamental physics. Based on conservative assumptions for the performance of the different CTA telescope configurations, we employ a Monte Carlo based approach to evaluate the prospects for detection. First, we discuss CTA prospects for cold dark matter searches, following different observational strategies: in dwarf satellite galaxies of the Milky Way, in the region close to the Galactic Centre, and in clusters of galaxies. The possible search for spatial signatures, facilitated by the larger field of view of CTA, is also discussed. Next we consider searches for axion-like particles which, besides being possible candidates for dark matter may also explain the unexpectedly low absorption by extragalactic background light of gamma rays from very distant blazars. Simulated light-curves of flaring sources are also used to determine the sensitivity to violations of Lorentz Invariance by detection of the possible delay between the arrival times of photons at different energies. Finally, we mention searches for other exotic physics with CTA.
The Cherenkov Telescope Array Large Size Telescope  [PDF]
G. Ambrosi,Y. Awane,H. Baba,A. Bamba,M. Barceló,U. Barres de Almeida,J. A. Barrio,O. Blanch Bigas,J. Boix,L. Brunetti,E. Carmona,E. Chabanne,M. Chikawa,P. Colin,J. L. Conteras,J. Cortina,F. Dazzi,A. Deangelis,G. Deleglise,C. Delgado,C. Díaz,F. Dubois,A. Fiasson,D. Fink,N. Fouque,L. Freixas,C. Fruck,A. Gadola,R. García,D. Gascon,N. Geffroy,N. Giglietto,F. Giordano,F. Gra?ena,S. Gunji,R. Hagiwara,N. Hamer,Y. Hanabata,T. Hassan,K. Hatanaka,T. Haubold,M. Hayashida,R. Hermel,D. Herranz,K. Hirotani,S. Inoue,Y. Inoue,K. Ioka,C. Jablonski,M. Kagaya,H. Katagiri,T. Kishimoto,K. Kodani,K. Kohri,Y. Konno,S. Koyama,H. Kubo,J. Kushida,G. Lamanna,T. Le Flour,M. López-Moya,R. López,E. Lorenz,P. Majumdar,A. Manalaysay,M. Mariotti,G. Martínez,M. Martínez,D. Mazin,J. M. Miranda,R. Mirzoyan,I. Monteiro,A. Moralejo,K. Murase,S. Nagataki,D. Nakajima,T. Nakamori,K. Nishijima,K. Noda,A. Nozato,Y. Ohira,M. Ohishi,H. Ohoka,A. Okumura,R. Orito,J. L. Panazol,D. Paneque,R. Paoletti,J. M. Paredes,G. Pauletta,S. Podkladkin,J. Prast,R. Rando,O. Reimann,M. Ribó,S. Rosier-Lees,K. Saito,T. Saito,Y. Saito,N. Sakaki,R. Sakonaka,A. Sanuy,H. Sasaki,M. Sawada,V. Scalzotto,S. Schultz,T. Schweizer,T. Shibata,S. Shu,J. Sieiro,V. Stamatescu,S. Steiner,U. Straumann,R. Sugawara,H. Tajima,H. Takami,S. Tanaka,M. Tanaka,L. A. Tejedor,Y. Terada,M. Teshima,T. Totani,H. Ueno,K. Umehara,A. Vollhardt,R. Wagner,H. Wetteskind,T. Yamamoto,R. Yamazaki,A. Yoshida,T. Yoshida,T. Yoshikoshi,for the CTA Consortium
Physics , 2013,
Abstract: The two arrays of the Very High Energy gamma-ray observatory Cherenkov Telescope Array (CTA) will include four Large Size Telescopes (LSTs) each with a 23 m diameter dish and 28 m focal distance. These telescopes will enable CTA to achieve a low-energy threshold of 20 GeV, which is critical for important studies in astrophysics, astroparticle physics and cosmology. This work presents the key specifications and performance of the current LST design in the light of the CTA scientific objectives.
Surveys with the Cherenkov Telescope Array  [PDF]
G. Dubus,J. L. Contreras,S. Funk,Y. Gallant,T. Hassan,J. Hinton,Y. Inoue,J. Kn?dlseder,P. Martin,N. Mirabal,M. de Naurois,M. Renaud,for the CTA consortium
Physics , 2012, DOI: 10.1016/j.astropartphys.2012.05.020
Abstract: Surveys open up unbiased discovery space and generate legacy datasets of long-lasting value. One of the goals of imaging arrays of Cherenkov telescopes like CTA is to survey areas of the sky for faint very high energy gamma-ray (VHE) sources, especially sources that would not have drawn attention were it not for their VHE emission (e.g. the Galactic "dark accelerators"). More than half the currently known VHE sources are to be found in the Galactic plane. Using standard techniques, CTA can carry out a survey of the region |l|<60 degrees, |b|<2 degrees in 250 hr (1/4th the available time per year at one location) down to a uniform sensitivity of 3 mCrab (a "Galactic Plane survey"). CTA could also survey 1/4th of the sky down to a sensitivity of 20 mCrab in 370 hr of observing time (an "all-sky survey"), which complements well the surveys by the Fermi/LAT at lower energies and extended air shower arrays at higher energies. Observations in (non-standard) divergent pointing mode may shorten the "all-sky survey" time to about 100 hr with no loss in survey sensitivity. We present the scientific rationale for these surveys, their place in the multi-wavelength context, their possible impact and their feasibility. We find that the Galactic Plane survey has the potential to detect hundreds of sources. Implementing such a survey should be a major goal of CTA. Additionally, about a dozen blazars, or counterparts to Fermi/LAT sources, are expected to be detected by the all-sky survey, whose prime motivation is the search for extragalactic "dark accelerators".
Cherenkov Telescope Array Data Management  [PDF]
G. Lamanna,L. A. Antonelli,J. L. Contreras,J. Kn?dlseder,K. Kosack,N. Neyroud,A. Aboudan,L. Arrabito,C. Barbier,D. Bastieri,C. Boisson,S. Brau-Nogué,J. Bregeon,A. Bulgarelli,A. Carosi,A. Costa,G. De Cesare,R. de los Reyes,V. Fioretti,S. Gallozzi,J. Jacquemier,B. Khelifi,J. Kocot,S. Lombardi,F. Lucarelli,E. Lyard,G. Maier,P. Massimino,J. P. Osborne,M. Perri,J. Rico,D. A. Sanchez,K. Satalecka,H. Siejkowski,T. Stolarczyk,T. Szepieniec,V. Testa,R. Walter,J. E. Ward,A. Zoli,for the CTA consortium
Physics , 2015,
Abstract: Very High Energy gamma-ray astronomy with the Cherenkov Telescope Array (CTA) is evolving towards the model of a public observatory. Handling, processing and archiving the large amount of data generated by the CTA instruments and delivering scientific products are some of the challenges in designing the CTA Data Management. The participation of scientists from within CTA Consortium and from the greater worldwide scientific community necessitates a sophisticated scientific analysis system capable of providing unified and efficient user access to data, software and computing resources. Data Management is designed to respond to three main issues: (i) the treatment and flow of data from remote telescopes; (ii) "big-data" archiving and processing; (iii) and open data access. In this communication the overall technical design of the CTA Data Management, current major developments and prototypes are presented.
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