Science with the Cherenkov Telescope Array The Cta Consortium, The Cta Consortium
The Astrophysical journal. Supplement series,
01/2019, Letnik:
240, Številka:
2
eBook, Journal Article, Book
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This book summarizes the science to be carried out by the upcoming Cherenkov Telescope Array, a major ground-based gamma-ray observatory that will be constructed over the next six to eight years. The ...major scientific themes, as well as core program of key science projects, have been developed by the CTA Consortium, a collaboration of scientists from many institutions worldwide. CTA will be the major facility in high-energy and very high-energy photon astronomy over the next decade and beyond. CTA will have capabilities well beyond past and present observatories. Thus, CTA's science program is expected to be rich and broad and will complement other major multiwavelength and multimessenger facilities. This book is intended to be the primary resource for the science case for CTA and it thus will be of great interest to the broader physics and astronomy communities. The electronic version (e-book) is available in open access.
Context.
Young massive stellar clusters are extreme environments and potentially provide the means for efficient particle acceleration. Indeed, they are increasingly considered as being responsible ...for a significant fraction of cosmic rays (CRs) that are accelerated within the Milky Way. Westerlund 1, the most massive known young stellar cluster in our Galaxy, is a prime candidate for studying this hypothesis. While the very-high-energy
γ
-ray source HESS J1646−458 has been detected in the vicinity of Westerlund 1 in the past, its association could not be firmly identified.
Aims.
We aim to identify the physical processes responsible for the
γ
-ray emission around Westerlund 1 and thus to understand the role of massive stellar clusters in the acceleration of Galactic CRs better.
Methods.
Using 164 h of data recorded with the High Energy Stereoscopic System (H.E.S.S.), we carried out a deep spectromorphological study of the
γ
-ray emission of HESS J1646−458. We furthermore employed H I and CO observations of the region to infer the presence of gas that could serve as target material for interactions of accelerated CRs.
Results.
We detected large-scale (∼2° diameter)
γ
-ray emission with a complex morphology, exhibiting a shell-like structure and showing no significant variation with
γ
-ray energy. The combined energy spectrum of the emission extends to several tens of TeV, and it is uniform across the entire source region. We did not find a clear correlation of the
γ
-ray emission with gas clouds as identified through H I and CO observations.
Conclusions.
We conclude that, of the known objects within the region, only Westerlund 1 can explain the majority of the
γ
-ray emission. Several CR acceleration sites and mechanisms are conceivable and discussed in detail. While it seems clear that Westerlund 1 acts as a powerful particle accelerator, no firm conclusions on the contribution of massive stellar clusters to the flux of Galactic CRs in general can be drawn at this point.
The CoMET is an R\(\&\)D project aiming to design a very-high-energy (VHE) gamma-ray observatory sensitive to energies above \(\sim\) 200 GeV. The science goals include continuous observation of ...soft-spectrum VHE gamma-ray sources such as Active Galactic Nuclei (AGNs) and transients like Gamma-Ray Bursts (GRBs). With these objectives, CoMET is designed to have a low energy threshold with a wide field-of-view of about 2 sr, at a high altitude, and combines ALTO particle detectors with CLiC air-Cherenkov detectors. In this contribution, we focus on the ALTO particle detector array performance only. Water Cherenkov detectors are used for the detection of secondary particles in atmospheric air showers while scintillators serve as muon counters. A detailed study is presented through air-shower, detector and trigger simulations, followed by the reconstruction of the event parameters and the extraction of the signal (gamma-rays) from the background (cosmic-rays). We present the sensitivity of the ALTO detectors to a list of astrophysical sources using two SEMLA analysis configurations.
In the context of atmospheric shower arrays designed for $\gamma$-ray
astronomy and in the context of the ALTO project, we present: a study of the
impact of heavier nuclei in the cosmic-ray ...background on the estimated
$\gamma$-ray detection performance on the basis of dedicated Monte Carlo
simulations, a method to calculate the sensitivity to a point-like source, and
finally the required observation times to reach a firm detection on a list of
known point-like sources.
We present the SEMLA (Signal Extraction using Machine Learning for ALTO)
analysis method, developed for the detection of $\rm E>200\,GeV$ $\gamma$ rays
in the context of the ALTO wide-field-of-view ...atmospheric shower array R&D
project. The scientific focus of ALTO is extragalactic $\gamma$-ray astronomy,
so primarily the detection of soft-spectrum $\gamma$-ray sources such as Active
Galactic Nuclei and Gamma Ray Bursts. The current phase of the ALTO R&D project
is the optimization of sensitivity for such sources and includes a number of
ideas which are tested and evaluated through the analysis of dedicated Monte
Carlo simulations and hardware testing. In this context, it is important to
clarify how data are analysed and how results are being obtained. SEMLA takes
advantage of machine learning and comprises four stages: initial event cleaning
(stage A), filtering out of poorly reconstructed $\gamma$-ray events (stage B),
followed by $\gamma$-ray signal extraction from proton background events (stage
C) and finally reconstructing the energy of the events (stage D). The
performance achieved through SEMLA is evaluated in terms of the angular, shower
core position, and energy resolution, together with the effective detection
area, and background suppression. Our methodology can be easily generalized to
any experiment, provided that the signal extraction variables for the specific
analysis project are considered.
In the context of atmospheric shower arrays designed for \(\gamma\)-ray astronomy and in the context of the ALTO project, we present: a study of the impact of heavier nuclei in the cosmic-ray ...background on the estimated \(\gamma\)-ray detection performance on the basis of dedicated Monte Carlo simulations, a method to calculate the sensitivity to a point-like source, and finally the required observation times to reach a firm detection on a list of known point-like sources.
We present the SEMLA (Signal Extraction using Machine Learning for ALTO) analysis method, developed for the detection of \(\rm E>200\,GeV\) \(\gamma\) rays in the context of the ALTO ...wide-field-of-view atmospheric shower array R&D project. The scientific focus of ALTO is extragalactic \(\gamma\)-ray astronomy, so primarily the detection of soft-spectrum \(\gamma\)-ray sources such as Active Galactic Nuclei and Gamma Ray Bursts. The current phase of the ALTO R&D project is the optimization of sensitivity for such sources and includes a number of ideas which are tested and evaluated through the analysis of dedicated Monte Carlo simulations and hardware testing. In this context, it is important to clarify how data are analysed and how results are being obtained. SEMLA takes advantage of machine learning and comprises four stages: initial event cleaning (stage A), filtering out of poorly reconstructed \(\gamma\)-ray events (stage B), followed by \(\gamma\)-ray signal extraction from proton background events (stage C) and finally reconstructing the energy of the events (stage D). The performance achieved through SEMLA is evaluated in terms of the angular, shower core position, and energy resolution, together with the effective detection area, and background suppression. Our methodology can be easily generalized to any experiment, provided that the signal extraction variables for the specific analysis project are considered.
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