Atmospheric muons play an important role in underwater/ice neutrino detectors. In this paper, a parameterisation of the flux of single and multiple muon events, their lateral distribution and of ...their energy spectrum is presented. The kinematics parameters were modelled starting from a full Monte Carlo simulation of the interaction of primary cosmic rays with atmospheric nuclei; secondary muons reaching the sea level were propagated in the deep water. The parametric formulas are valid for a vertical depth of 1.5–5
km.w.e. and up to 85° for the zenith angle, and can be used as input for a fast simulation of atmospheric muons in underwater/ice detectors.
A new background rejection strategy for
γ-ray astrophysics with stereoscopic Imaging Atmospheric Cherenkov Telescopes (IACT), based on Monte Carlo (MC) simulations and real background data from the ...H.E.S.S. High Energy Stereoscopic System, see
1. experiment, is described. The analysis is based on a multivariate combination of both previously-known and newly-derived discriminant variables using the physical shower properties, as well as its multiple images, for a total of eight variables. Two of these new variables are defined thanks to a new energy evaluation procedure, which is also presented here. The method allows an enhanced sensitivity with the current generation of ground-based Cherenkov telescopes to be achieved, and at the same time its main features of rapidity and flexibility allow an easy generalization to any type of IACT. The robustness against Night Sky Background (NSB) variations of this approach is tested with MC simulated events. The overall consistency of the analysis chain has been checked by comparison of the real
γ-ray signal obtained from H.E.S.S. observations with MC simulations and through reconstruction of known source spectra. Finally, the performance has been evaluated by application to faint H.E.S.S. sources. The gain in sensitivity as compared to the best standard
Hillas analysis ranges approximately from 1.2 to 1.8 depending on the source characteristics, which corresponds to an economy in observation time of a factor 1.4 to 3.2.
Abstract
We present the SEMLA (Signal Extraction using Machine
Learning for ALTO) analysis method, developed for the detection of
E>200 GeV γ rays in the context of the ALTO
wide-field-of-view ...atmospheric shower array R&D project. The
scientific focus of ALTO is extragalactic γ-ray astronomy, so
primarily the detection of soft-spectrum γ-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 γ-ray events (stage B), followed by
γ-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.
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
Recenzirano
Odprti dostop
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.
The energy spectrum of neutrino-induced upward-going muons in MACRO has been analysed in terms of relativity principles violating effects, keeping standard mass-induced atmospheric neutrino ...oscillations as the dominant source of νμ→ντ transitions. The data disfavor these exotic possibilities even at a subdominant level, and stringent 90% C.L. limits are placed on the Lorentz invariance violation parameter |Δv|<6×10−24 at sin2θv=0 and |Δv|<2.5–5×10−26 at sin2θv=±1. These limits can also be re-interpreted as upper bounds on the parameters describing violation of the equivalence principle.
Very high energy (VHE; E > or =, slanted E 100 GeV) and high-energy (HE; 100 MeV < or =, slanted E < or =, slanted 100 GeV) data from gamma-ray observations performed with the H.E.S.S. telescope ...array and the Fermi-LAT instrument, respectively, are analyzed in order to investigate the non-thermal processes in the starburst galaxy NGC 253. A power-law fit to the differential HE gamma-ray spectrum reveals a photon index of Gamma = 2.24 + or - 0.14 sub(stat) + or - 0.03 sub(sys) and an integral flux between 200 MeV and 200 GeV of F(0.2-200 GeV) = (4.9 + or - 1.0 sub(stat) + or - 0.3 sub(sys)) x 10 super(-9) cm super(-2) s super(-1). No evidence for a spectral break or turnover is found over the dynamic range of both the LAT instrument and the H.E.S.S. experiment: a combined fit of a power law to the HE and VHE gamma-ray data results in a differential photon index Gamma = 2.34 + or - 0.03 with a p-value of 30%..
► Extensive simulations for the design and optimization of CTA were carried out. ► Different sets of simulation tools were checked against each other. ► Large-scale simulations with 275 telescopes ...for later layout selection.► Different analysis methods were applied and compared. ► Resulting sensitivity predictions confirmed the goals of CTA.
The Cherenkov Telescopes Array (CTA) is planned as the future instrument for very-high-energy (VHE) gamma-ray astronomy with a wide energy range of four orders of magnitude and an improvement in sensitivity compared to current instruments of about an order of magnitude. Monte Carlo simulations are a crucial tool in the design of CTA. The ultimate goal of these simulations is to find the most cost-effective solution for given physics goals and thus sensitivity goals or to find, for a given cost, the solution best suited for different types of targets with CTA. Apart from uncertain component cost estimates, the main problem in this procedure is the dependence on a huge number of configuration parameters, both in specifications of individual telescope types and in the array layout. This is addressed by simulation of a huge array intended as a superset of many different realistic array layouts, and also by simulation of array subsets for different telescope parameters. Different analysis methods – in use with current installations and extended (or developed specifically) for CTA – are applied to the simulated data sets for deriving the expected sensitivity of CTA. In this paper we describe the current status of this iterative approach to optimize the CTA design and layout.
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 Large Magellanic Cloud, a satellite galaxy of the Milky Way, has been observed with the High Energy Stereoscopic System (H.E.S.S.) above an energy of 100 billion electron volts for a deep ...exposure of 210 hours. Three sources of different types were detected: the pulsar wind nebula of the most energetic pulsar known, N 157B; the radio-loud supernova remnant N 132D; and the largest nonthermal x-ray shell, the superbubble 30 Dor C. The unique object SN 1987A is, unexpectedly, not detected, which constrains the theoretical framework of particle acceleration in very young supernova remnants. These detections reveal the most energetic tip of a γ-ray source population in an external galaxy and provide via 30 Dor C the unambiguous detection of γ-ray emission from a superbubble.
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