Identification of Cherenkov light generated by muons has been suggested as a promising way to dramatically improve the background rejection power of Imaging Atmospheric Cherenkov Telescope (IACT) ...arrays at high energies. However, muon identification remains a challenging task, for which efficient algorithms are still being developed. We present an approach in which, rather than identifying Cherenkov light from muons, we simply consider the presence of Cherenkov light other than the main shower image in IACTs with large mirror area. We show that in the case of the H.E.S.S. array of five telescopes this approach results in background rejection improvements at all energies above 1 TeV. In particular, the rejection power can be improved by a factor
∼
3
–4 at energies above 20 TeV while keeping
∼
90
%
of the original gamma-ray efficiency.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The Earth’s atmosphere is an integral part of the detector in ground-based imaging atmospheric Cherenkov telescope (IACT) experiments and has to be taken into account in the calibration. Atmospheric ...and hardware-related deviations from simulated conditions can result in the mis-reconstruction of primary particle energies and therefore of source spectra. During the eight years of observations with the High Energy Stereoscopic System (H.E.S.S.) in Namibia, the overall yield in Cherenkov photons has varied strongly with time due to gradual hardware aging, together with adjustments of the hardware components, and natural, as well as anthropogenic, variations of the atmospheric transparency. Here we present robust data selection criteria that minimize these effects over the full data set of the H.E.S.S. experiment and introduce the Cherenkov transparency coefficient as a new atmospheric monitoring quantity. The influence of atmospheric transparency, as quantified by this coefficient, on energy reconstruction and spectral parameters is examined and its correlation with the aerosol optical depth (AOD) of independent MISR satellite measurements and local measurements of atmospheric clarity is investigated.
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.
Pulsar wind nebulae are a prominent class of very high energy (E > 0.1 TeV) Galactic sources. Their Gamma-ray spectra are interpreted as due to inverse Compton scattering of ultrarelativistic ...electrons on the ambient photons, whereas the X-ray spectra are due to synchrotron emission. We investigate the relation between the Gamma- and-X-ray emission and the pulsars' spin-down luminosity and characteristic age. We find that the distance-independent Gamma- to X-ray flux ratio of the nebulae is inversely proportional to the spin-down luminosity, (\propto \dot{E}^-1.9), while it appears proportional to the characteristic age, (\propto tau_c^2.2), of the parent pulsar. We interpret these results as due to the evolution of the electron energy distribution and the nebular dynamics, supporting the idea of so-called relic pulsar wind nebulae. These empirical relations provide a new tool to classify unidentified diffuse Gamma-ray sources and to estimate the spin-down luminosity and characteristic age of rotation powered pulsars with no detected pulsation from the X- and Gamma-ray properties of the associated pulsar wind nebulae. We apply these relations to predict the spin-down luminosity and characteristic age of four (so far unpulsing) candidate pulsars associated to wind nebulae.
We report the discovery of 31.18 ms pulsations from the INTEGRAL source IGR J14003-6326 using the Rossi X-ray Timing Explorer (RXTE). This pulsar is most likely associated with the bright Chandra ...X-ray point source lying at the center of G310.6-1.6, a previously unrecognized Galactic composite supernova remnant (SNR) with a bright central non-thermal radio and X-ray nebula, taken to be the pulsar wind nebula (PWN). PSR J1400-6325 is amongst the most energetic rotation-powered pulsars in the Galaxy, with a spin-down luminosity of \dot{E} = 5.1 × 10^{37} erg s-1. In the rotating dipole model, the surface dipole magnetic field strength is Bs = 1.1 × 1012 G and the characteristic age τ_c ≡ P/2\dot{P} = 12.7 kyr. The high spin-down power is consistent with the hard spectral indices of the pulsar and the nebula of 1.22 ± 0.15 and 1.83 ± 0.08, respectively, and a 2-10 keV flux ratio F PWN/F PSR ~ 8. Follow-up Parkes observations resulted in the detection of radio emission at 10 and 20 cm from PSR J1400-6325 at a dispersion measure of ~560 cm-3 pc, which implies a relatively large distance of 10 ± 3 kpc. However, the resulting location off the Galactic plane of ~280 pc would be much larger than the typical thickness of the molecular disk, and we argue that G310.6-1.6 lies at a distance of ~7 kpc. There is no gamma-ray counterpart to the nebula or pulsar in the Fermi data published so far. A multi-wavelength study of this new composite SNR, from radio to very high-energy gamma rays, suggests a young (lsim103 yr) system formed by a sub-energetic (lsim1050 erg), low ejecta mass (M ej ~ 3 M sun) supernova explosion that occurred in a low-density environment (n 0~ 0.01 cm-3).
Recurrent novae are repeating thermonuclear explosions in the outer layers of white dwarfs, due to the accretion of fresh material from a binary companion. The shock generated when ejected material ...slams into the companion star's wind can accelerate particles. We report very-high-energy (VHE; Formula: see text) gamma rays from the recurrent nova RS Ophiuchi, up to 1 month after its 2021 outburst, observed using the High Energy Stereoscopic System (H.E.S.S.). The temporal profile of VHE emission is similar to that of lower-energy giga-electron volt emission, indicating a common origin, with a 2-day delay in peak flux. These observations constrain models of time-dependent particle energization, favoring a hadronic emission scenario over the leptonic alternative. Shocks in dense winds provide favorable environments for efficient acceleration of cosmic rays to very high energies.
This paper presents an analysis of the updated version of the Front-End Board (FEB) for the NectarCAM camera, developed for the Cherenkov Telescope Array Observatory (CTAO). The FEB is a critical ...component responsible for reading and converting signals from the camera’s photo-multiplier tubes into digital data and generating module-level trigger signals. This study provides an overview of the design and performance of the new FEB version, including the use of an improved NECTAr3 chip with advanced features. The NECTAr3 chip contains a switched capacitor array for sampling signals at 1 GHz and a 12-bit analog-to-digital converter (ADC) for digitization upon receiving a trigger signal. The integration of the new NECTAr3 chip results in a significant reduction of NectarCAM’s deadtime by an order of magnitude compared to the previous version. The paper also presents the results of laboratory testing, including measurements of timing performance, linearity, dynamic range, and deadtime, to characterize the new FEB’s performance.
This paper presents an analysis of the updated version of the Front-End Board (FEB) for the NectarCAM camera, developed for the Cherenkov Telescope Array Observatory (CTAO). The FEB is a critical ...component responsible for reading and converting signals from the camera's photo-multiplier tubes into digital data and generating module-level trigger signals. This study provides an overview of the design and performance of the new FEB version, including the use of an improved NECTAr3 chip with advanced features. The NECTAr3 chip contains a switched capacitor array for sampling signals at 1 GHz and a 12-bit analog-to-digital converter (ADC) for digitization upon receiving a trigger signal. The integration of the new NECTAr3 chip results in a significant reduction of NectarCAM's deadtime by an order of magnitude compared to the previous version. The paper also presents the results of laboratory testing, including measurements of timing performance, linearity, dynamic range, and deadtime, to characterize the new FEB's performance.
The High Energy Stereoscopic System (H.E.S.S.) is one of the three arrays of imaging atmospheric Cherenkov telescopes (IACTs) currently in operation. It is composed of four 12-meter telescopes and a ...28-meter one, and is sensitive to gamma rays in the energy range ~ 30 GeV – 100 TeV. The cameras of the 12-m telescopes recently underwent a substantial upgrade, with the goal of improving their performance and robustness. The upgrade involved replacing all camera components except for the photomultiplier tubes (PMTs). This meant developing new hardware for the trigger, readout, power, cooling and mechanical systems, and new software for camera control and data acquisition. Several novel technologies were employed in the cameras: the readout is built around the new NECTAr digitizer chip, developed for the next generation of IACTs; the camera electronics is fully controlled and read out via Ethernet using a combination of FPGA and embedded ARM computers; the software uses modern libraries such as Apache Thrift, ØMQ and Protocol buffers. This work describes in detail the design and the performance of the upgraded cameras.
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