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CTAO Instrument Response Functions - prod5 version v0.1
No full textCTAO Instrument Response Functions - prod5 version v0.1 The CTA Observatory (CTAO) will provide very wide energy range and excellent angular resolution and sensitivity in comparison to any existing gamma-ray detector. Energies down to 20 GeV will allow CTAO to study the most distant objects. Energies up to 300 TeV will push CTAO beyond the edge of the known electromagnetic spectrum, providing a completely new view of the sky. This data repository provides access to performance evaluation and instrument response functions (IRFs) for CTA. IRF version: prod5 v0.1 Telescope model and site configuration: prod5-model Publication date: Sep 2021 Archived webpage with performance figures included: CTAO Performance Description (file Website.md) Licence: this work is licensed under a Creative Commons Attribution 4.0 International License . Please use the contact address [email protected] for any inquiries. Citation and Acknowledgements: In cases for which the CTA instrument response functions are used in a research project, we ask to add the following acknowledgement in any resulting publication: 'This research has made use of the CTA instrument response functions provided by the CTA Consortium and Observatory, see https://www.ctao-observatory.org/science/cta-performance/ (version prod5 v0.1; [citation]) for more details.' Please use the following BibTex Entry for [citation] in the reference section of your publication: https://zenodo.org/record/5499840/export/hx Description Monte Carlo Simulations: The performance values are derived from detailed Monte Carlo (MC) simulations of the CTA instrument based on the CORSIKA air shower code (v7.71, with the hadronic interaction models QGSjet-II-04 and URQMD, [1]) and telescope simulation tool sim_telarray [2]. A power- law gamma-ray spectrum with photon index 2.62 was assumed in the calculations, although none of the instrument response functions (e.g. differential flux sensitivities, effective areas, angular or energy resolutions) depends on the assumed spectral shape of the gamma-ray source. Background cosmic-ray spectra of proton and electron/positron particle types are modelled according to recent measurements from cosmic-ray instruments. Nominal telescope pointing is assumed, with all telescopes pointing directions parallel to each other (performance estimation for other pointing modes, e.g. divergent pointing will be provided in the future). Performance estimations are available for three zenith angles (20 deg, 40 deg, and 60 deg), and for each zenith angle for two different azimuth angles (corresponding to pointing towards the magnetic North and South). There are significant performance differences found between the two azimuthal pointing directions (especially for the Northern site) as the impact of the geomagnetic field is large enough to influence notably the air shower development. For general studies, the use of the azimuth-averaged instrument response functions is recommended. Instrument Response Functions (IRFs): The analysis has been tuned to maximize the performance in terms of flux sensitivity. The optimal analysis cuts depend on the duration of the observation, therefore the IRFs are provided for 3 different observation times, from 0.5 to 50 h. IRFs are provided as binned histogram or FITS tables. It should be stressed, that the full potential of CTA in terms of angular and energy resolution is not revealed by these IRFS, due to the focus on the optimisation for best flux sensitivity. In general all histograms are binned with a 0.2-binning on the logarithmic energy axis (5 bins per decade); some selected histograms (e.g. effective areas or energy migration matrices) are provided with a finer binning. Effective area and energy migration matrix are available in a double version: one for the case in which there is no a priori knowledge of the true direction of incoming gamma rays (e.g. for the observation of diffuse sources), and another for observations of point-like objects (including among the analysis cuts one on the angle between the true and the reconstructed gamma-ray direction). IRFs are provided in ROOT format and as FITS tables. The FITS tables can be used directly as input to science analysis tools. The values of the IRFs are identical for the different file format, with one exception: the angular point-spread function is approximated by a Gaussian function for the FITS tables, while the ROOT files contain the full distribution. Telescope layouts are preliminary and subject to change. The following array layouts (Alpha configuration) have been assumed: CTA South with 14 MSTs and 37 SSTs (see [figure](figures/CTA-Performance-prod5-v0.1-South-Alpha-Layout.png)) CTA North with 4 LSTs and 9 MSTs (see [figure](figures/CTA-Performance-prod5-v0.1-North-Alpha-Layout.png)) Two zip files are uploaded: full archive with IRFs in FITS and ROOT format: cta-prod5-zenodo-v0.1.zip partial archive with IRFs in FITS format only: cta-prod5-zenodo-fitsonly-v0.1.zip File Naming (examples): Prod5-North-40deg-AverageAz-4LSTs09MSTs.18000s-v0.1.root: IRF for CTA Northern site on La Palma, 40 deg zenith angle, azimuth-averaged pointing, optimised for 5 hours of observation time Prod5-South-20deg-AverageAz-14MSTs37SSTs.180000s-v0.1.fits.gz: IRF for CTA Southern site in Paranal, 20 deg zenith angle, azimuth-averaged pointing, optimised for 50 hours of observation time List of files: FITS format: fits/CTA-Performance-prod5-v0.1-North-20deg.FITS.tar.gz fits/CTA-Performance-prod5-v0.1-North-40deg.FITS.tar.gz fits/CTA-Performance-prod5-v0.1-North-60deg.FITS.tar.gz fits/CTA-Performance-prod5-v0.1-South-20deg.FITS.tar.gz fits/CTA-Performance-prod5-v0.1-South-40deg.FITS.tar.gz fits/CTA-Performance-prod5-v0.1-South-60deg.FITS.tar.gz ROOT format: root/CTA-Performance-prod5-v0.1-North-20deg.tar.gz root/CTA-Performance-prod5-v0.1-North-40deg.tar.gz root/CTA-Performance-prod5-v0.1-North-60deg.tar.gz root/CTA-Performance-prod5-v0.1-South-20deg.tar.gz root/CTA-Performance-prod5-v0.1-South-40deg.tar.gz root/CTA-Performance-prod5-v0.1-South-60deg.tar.gz IRFs for subarrays of e.g., MSTs only are in the files named MSTSubArray (similar for all other telescope types). References [1] https://www.ikp.kit.edu/corsika/ [2] Bernloehr, K. 2008, Astroparticle Physics, 30, 149 Acknowledgements We would like to thank the computing centres that provided resources for the generation of the Prod 5 Instrument Response Functions (IRFs): CAMK, Nicolaus Copernicus Astronomical Center, Warsaw, Poland CIEMAT-LCG2, CIEMAT, Madrid, Spain CYFRONET-LCG2, ACC CYFRONET AGH, Cracow, Poland DESY-ZN, Deutsches Elektronen-Synchrotron, Standort Zeuthen, Germany GRIF, Grille de Recherche d’Ile de France, Paris, France IN2P3-CC, Centre de Calcul de l’IN2P3, Villeurbanne, France IN2P3-CPPM, Centre de Physique des Particules de Marseille, Marseille, France IN2P3-LAPP, Laboratoire d Annecy de Physique des Particules, Annecy, France INFN-FRASCATI, INFN Frascati, Frascati, Italy INFN-T1, CNAF INFN, Bologna, Italy INFN-TORINO, INFN Torino, Torino, Italy MPIK, Heidelberg, Germany OBSPM, Observatoire de Paris Meudon, Paris, France PIC, port d’informacio cientifica, Bellaterra, Spain prague_cesnet_lcg2, CESNET, Prague, Czech Republic praguelcg2, FZU Prague, Prague, Czech Republic UKI-NORTHGRID-LANCS-HEP, Lancaster University, United Kingdo
night and moon observations of the HEGRA Cherenkov telescope
No full textDuring the 1997 outburst of Mkn 501 extended observations in the presence of moonlight have been carried out with the HEGRA Cherenkov telescope CT1. Here we present the Mkn 501 energy spectrum derived from this moon data as well as the combined moon and no-moon spectrum extending well above 10 TeV
A Compact High Energy Camera (CHEC) for the Gamma-ray Cherenkov Telescope of the Cherenkov Telescope Array
No full textThe Gamma-ray Cherenkov Telescope (GCT) is one of the Small Size Telescopes (SSTs) proposed for the Cherenkov Telescope Array (CTA) aimed at the 1 TeV to 300 TeV energy range. GCT will be equipped with a Compact High-Energy Camera (CHEC) containing 2048 pixels of physical size about 66~mm, leading to a field of view of over 8 degrees. Electronics based on custom TARGET ASICs and FPGAs sample incoming signals at a gigasample per second and provide a flexible triggering scheme. Waveforms for every pixel in every event are read out are on demand without loss at over 600 events per second. A GCT prototype in Meudon, Paris saw first Cherenkov light from air showers in late 2015, using the first CHEC prototype, CHEC-M. This contribution presents results from lab and field tests with CHEC-M and the progress made to a robust camera design for deployment within CTA
Galactic transient sources with the Cherenkov Telescope Array
No full textA wide variety of Galactic sources show transient emission at soft and hard
X-ray energies: low-mass and high-mass X-ray binaries containing compact
objects (e.g., novae, microquasars, transitional millisecond pulsars,
supergiant fast X-ray transients), isolated neutron stars exhibiting extreme
variability as magnetars as well as pulsar wind nebulae. Although most of them
can show emission up to MeV and/or GeV energies, many have not yet been
detected in the TeV domain by Imaging Atmospheric Cherenkov Telescopes. In this
paper, we explore the feasibility of detecting new Galactic transients with the
Cherenkov Telescope Array (CTA) and the prospects for studying them with Target
of Opportunity observations. We show that CTA will likely detect new sources in
the TeV regime, such as the massive microquasars in the Cygnus region, low-mass
X-ray binaries with low-viewing angle, flaring emission from the Crab
pulsar-wind nebula or other novae explosions, among others. We also discuss the
multi-wavelength synergies with other instruments and large astronomical
facilities.Comment: 31 pages, 22 figures, submitted to MNRA
Simulation studies of the imaging atmospheric cherenkov technique using the Durham mark 6 and H.E.S.S. stand-alone telescopes
No full textThe subject of this thesis is the simulation study of the development of extensive air show ers produced by very high energy gamma-ray and hadronic cosmic rays with respect to the Cherenkov light they produce, and its imaging in ground based telescopes. Chapters 1-4 are introductory: Chapter 1 covers the mechanisms responsible for the production of very high energy gamma-rays, whereas, chapter 2 focusses on the development of extensive air showers and Cherenkov light production. Chapter 3 covers the instrumentation used to measure the Cherenkov light using the imaging atmospheric Cherenkov technique. Chapter 4 covers known and possible sources of very high energy gamma-rays. Chapters 5, 6 and 7 cover research performed by the author: Chapter 5 discusses some of the differences between three popular extensive air shower simulations codes, namely ALTAI, CORSIKA and MOCCA. Chapter 6 details the simulation of the response of two ground based imaging atmospheric Cherenkov telescope (the Durham Mark 6 and stand-alone H.E.S.S. telescopes), and in particular details the derivation of the flux of the x-ray selected BL-LAC PKS 2155-304 with the Durham Mark 6 telescope. This represents the refinement of a published measurement given an improved telescope simulation. The significance of the signal seen is 6.8o, and the integral flux derived above 1.5 TeV (assuming a differential spectral slope of-2.6) is {2.5±0.7stat ± (^0.5)(_1.6syst) x 10(^-7) photons m(^-2) s(^-1) Chapter 7 discusses the importance of the atmosphere, and the results of shower simulations under different atmospheric assumptions are presented, which indicate the importance of atmospheric calibration for the new generation of Cherenkov telescopes. The results of this chapter suggest that to first order large changes in the low level aerosol concentration have a much more significant effect on the trigger rate of a stand-alone H.E.S.S. telescope, than on the Hillas parameter distributions seen. Chapter 8 brings together the work done in this thesis, and highlights a final set of fluxes for the active galactic nuclei sources seen with the Durham Mark 6 telescope, many of which will form future sources to be measured with the H.E.S.S. system. The current status of the stand-alone H.E.S.S. system is also covered in chapter 8. The thesis concludes with a further brief discussion of the future prospects for imaging atmospheric Cherenkov astronomy
The effects of atmosphere conditions on gamma-ray astronomy
No full textThe High Energetic Stereoscopic System (H.E.S.S.) experiment is an array of imaging atmospheric Cherenkov (IAC) telescopes of the next generation, with enlarged mirrors and advanced detector electronics compared to its predecessors. As a member of the international H.E.S.S. collaboration, the Durham 7-rау astronomy group took over the responsibility for design, construction and commissioning of calibration systems for the H.E.S.S. telescopes and atmospheric monitoring devices. The atmosphere is an essential part of the detector system for the IAC technique, monitoring of the atmosphere's parameter is therefore important for energy calibration of the detector and variability studies of 7-ray sources to distinguish between detector and source fluctuations. A weather station, several infrared radiometers and an infrared LIDAR system have been installed to provide constant monitoring of all relevant parameters. This thesis reports about the work performed for the design and commissioning of the calibration module. Furthermore, the technicalities of the LIDAR system and the IR radiometer, their use in terms of 7-ray astronomy, especially studies about the variability of zenith angle dependencies and the correlation with other atmospheric parameters and telescope trigger rates are discussed
Sensitivity of the Cherenkov Telescope Array to a dark matter signal from the Galactic centre
No full textWe 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
A Monte Carlo simulation study for cosmic-ray chemical composition measurement with Cherenkov Telescope Array
No full textOur Galaxy is filled with cosmic-ray particles and more than 98% of them are atomic nuclei. In order to clarify their origin and acceleration mechanism, chemical composition measurements of these cosmic rays with wide energy coverage play an important role. Imaging Atmospheric Cherenkov Telescope (IACT) arrays are designed to detect cosmic gamma-rays in the very-high-energy regime (TeV). Recently these systems proved to be capable of measuring cosmic-ray chemical composition in the sub-PeV region by capturing direct Cherenkov photons emitted by charged primary particles. Extensive air shower profiles measured by IACTs also contain information about the primary particle type since the cross section of inelastic scattering in the air depends on the primary mass number. The Cherenkov Telescope Array (CTA) is the next generation IACT system, which will consist of multiple types of telescopes and have a km-scale footprint and extended energy coverage (20 GeV to 300 TeV). In order to estimate CTA potential for cosmic ray composition measurement, a full Monte Carlo simulation including a description of extensive air shower and detector response is needed. We generated a number of cosmic-ray nuclei events (8 types selected from H to Fe) for a specific CTA layout candidate in the southern-hemisphere site. We applied Direct Cherenkov event selection and shower profile analysis to these data and preliminary results on charge number resolution and expected event count rate for these cosmic-ray nuclei are presented
The gamma-ray Cherenkov telescope for the Cherenkov telescope array
No full textThe Cherenkov Telescope Array (CTA) is a forthcoming ground-based observatory for very-high-energy gamma rays. CTA will consist of two arrays of imaging atmospheric Cherenkov telescopes in the Northern and Southern hemispheres, and will combine telescopes of different types to achieve unprecedented performance and energy coverage. The Gamma-ray Cherenkov Telescope (GCT) is one of the small-sized telescopes proposed for CTA to explore the energy range from a few TeV to hundreds of TeV with a field of view ≳ 8° and angular resolution of a few arcminutes. The GCT design features dual-mirror Schwarzschild-Couder optics and a compact camera based on densely-pixelated photodetectors as well as custom electronics. In this contribution we provide an overview of the GCT project with focus on prototype development and testing that is currently ongoing. We present results obtained during the first on-telescope campaign in late 2015 at the Observatoire de Paris-Meudon, during which we recorded the first Cherenkov images from atmospheric showers with the GCT multi-anode photomultiplier camera prototype. We also discuss the development of a second GCT camera prototype with silicon photomultipliers as photosensors, and plans toward a contribution to the realisation of CTA
Sensitivity of the Cherenkov Telescope Array to spectral signatures of hadronic PeVatrons with application to Galactic Supernova Remnants
No full textThe local Cosmic Ray (CR) energy spectrum exhibits a spectral softening at energies around 3 PeV. Sources which are capable of accelerating hadrons to such energies are called hadronic PeVatrons. However, hadronic PeVatrons have not yet been firmly identified within the Galaxy. Several source classes, including Galactic Supernova Remnants (SNRs), have been proposed as PeVatron candidates. The potential to search for hadronic PeVatrons with the Cherenkov Telescope Array (CTA) is assessed. The focus is on the usage of very high energy γ-ray spectral signatures for the identification of PeVatrons. Assuming that SNRs can accelerate CRs up to knee energies, the number of Galactic SNRs which can be identified as PeVatrons with CTA is estimated within a model for the evolution of SNRs. Additionally, the potential of a follow-up observation strategy under moonlight conditions for PeVatron searches is investigated. Statistical methods for the identification of PeVatrons are introduced, and realistic Monte-Carlo simulations of the response of the CTA observatory to the emission spectra from hadronic PeVatrons are performed. Based on simulations of a simplified model for the evolution for SNRs, the detection of a γ-ray signal from in average 9 Galactic PeVatron SNRs is expected to result from the scan of the Galactic plane with CTA after 10 h of exposure. CTA is also shown to have excellent potential to confirm these sources as PeVatrons in deep observations with (100) hours of exposure per source
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