arXiv subjects

Vincent Marandon

Publications and source records attributed to Vincent Marandon.

12 recordsLinked to original sources

arXiv2025

Design and characterization of the Flat-Field Calibration of the NectarCAM Camera

The NectarCAM flat-field flasher is a calibration device designed for the camera that will equip the Medium-Sized Telescopes (MSTs) of the northern site of the Cherenkov Telescope Array Observatory (CTAO). Positioned in the centre of the MST dish, 16 meters in front of the camera, the flasher emits short (FWHM $\approx$ 5 ns), uniform (2$-$4%) light pulses to illuminate the entire focal plane. Accurate calibration is crucial for the optimal operation of the NectarCAM, ensuring precise gain computation and mitigating differences in light-collection efficiency of the pixels of the camera. Using the flat-field flasher, two informations are obtained : the pixel gain and the relative efficiency between pixels. In addition, the flasher is used to probe the dynamic range over which the camera operates effectively. In this study, we report on the performance characterisation of the flat-field flasher using a dedicated test bench. We report on the results of tests conducted on several flasher units, evaluating their reliability. Furthermore, we describe how the flat-field coefficients are applied within the camera to ensure uniformity of response of few percent level across all 1855 pixels. As the deployment of the first MST at the CTAO northern site is scheduled for 2027, this work represents a significant contribution to the collaboration`s efforts to finalize camera calibration systems.

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arXiv2023

$\texttt{nectarchain}$, the scientific software for the Cherenkov Telescope Array -- NectarCAM

The NectarCAM is a camera that will be mounted on the Medium-Sized Telescopes of the Cherenkov Telescope Array (CTA) observatory. Along with the hardware integration of the camera, the scientific software, $\texttt{nectarchain}$, is being developed. The software is responsible for transforming the raw data from the camera into analysis-ready calibrated data. In this contribution, we present the structure of the software, which consists of two modules: the calibration pipeline and the data quality check pipeline. The calibration pipeline reduces the data, performs flat fielding, and determines the gain for the analysis. The data quality monitoring pipeline is used to select the data that meets the necessary standards for analysis. Additionally, we discuss the format of the downstream data and the integration of the $\texttt{nectarchain}$ modules in the general software framework of CTA. We also present the necessary tests for validating each part of the code. We conclude by mentioning the prospects for the future of the software.

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arXiv2022

Background rejection using image residuals from large telescopes in imaging atmospheric Cherenkov telescope arrays

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 $\sim3-4$ at energies above 20 TeV while keeping $\sim90\%$ of the original gamma-ray efficiency.

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arXiv2021

Science verification of the new FlashCam-based camera in the 28m telescope of H.E.S.S

In October 2019 the central 28m telescope of the H.E.S.S. experiment has been upgraded with a new camera. The camera is based on the FlashCam design which has been developed in view of a possible future implementation in the medium-sized telescopes of the Cherenkov Telescope Array (CTA). We report here on the results of the science verification program that has been performed after commissioning of the new camera, to show that the camera and software pipelines are working up to expectations.

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arXiv2020

A NECTAr-based upgrade for the Cherenkov cameras of the H.E.S.S. 12-meter telescopes

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, ZMQ and Protocol buffers. This work describes in detail the design and the performance of the upgraded cameras.

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arXiv2019

Latest news from the HAWC outrigger array

The High Altitude Water Cherenkov (HAWC) observatory is a very high energy gamma-ray detector located in Mexico. In late 2018, the HAWC collaboration completed a major upgrade consisting of the addition of a sparse outrigger array of 345 small water Cherenkov detectors (WCDs) surrounding the 300 WCDs of the main array and extending the instrumented area by a factor of 4. It provides an improved reconstruction of the showers whose core and footprint are not well contained in the array and increases the effective area in the range of a few TeV to beyond 100 TeV. This improvement in sensitivity will help to have a better understanding of the Galactic sources that accelerate particles up to the knee of the cosmic ray spectrum. In this contribution, we will show the current status, the performance, and the first results from the HAWC outrigger array.

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arXiv2019

A complementary view of the Galactic plane in TeV gamma rays by HAWC and H.E.S.S

The H.E.S.S. collaboration recently published its Galactic Plane Survey, which is a deep survey of half of the Milky Way in TeV gamma-rays, using almost 10 years of observations. It contains 78 sources, including 16 new sources. On the other hand, the HAWC collaboration also published its 2HWC catalogue based on 507 days of data. It is the result of the first source search performed with the complete HAWC detector, covering two thirds of the sky. In this search, 39 sources have been reported, amongst them 16 detected for the first time at TeV energies. The HAWC data set doubled since then, revealing 10 more sources. Both instruments are very different in terms of conception, observation and regarding event analysis and reconstruction, but they operate at a similar energy range. In a sense, they are very complementary. I will present a comparison of the Galactic plane seen by both instruments in the overlapping region, highlight the similarities and differences which arise from intrinsic properties of the instruments and from their dedicated data analysis, and show that background estimation is a major ingredient.

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arXiv2013

Study of the Very High Energy emission from Supernova Remnants with H.E.S.S

From radio and higher-frequency observations, more than 300 SNRs have been discovered in the Milky Way, of which 220 fall into the H.E.S.S. Galactic Plane Survey. However only 50 SNRs are coincident with a H.E.S.S source and in 8 cases the VHE emission is firmly associated with the SNR. The H.E.S.S. dataset includes now more than 8 years of observations and it is of great interest to extract VHE flux upper limits from undetected SNRs. These new measurements can then be used to test the standard paradigm of the SNRs as the origin of Galactic cosmic rays. In this contribution, the H.E.S.S. results on the population of SNRs and the subsequent constraints on the cosmic-ray acceleration efficiency in these sources will be presented.

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arXiv2012

Exploring the Galaxy at TeV energies: Latest results from the H.E.S.S. Galactic Plane Survey

The High Energy Stereoscopic System (H.E.S.S.) is an array of four imaging atmospheric-Cherenkov telescopes located in Namibia and designed to detect extensive air showers initiated by gamma-rays in the very-high-energy domain. It is an ideal instrument for surveying the Galactic plane in search of new sources, thanks to its location in the Southern Hemisphere, its excellent sensitivity, and its large field-of-view. The efforts of the H.E.S.S. Galactic Plane Survey, the first comprehensive survey of the inner Galaxy at TeV energies, have contributed to the discovery of an unexpectedly large and diverse population of over 60 sources of VHE gamma rays within its current range of l=250 to 65 degrees in longitude and |b|<=3.5 degrees in latitude. The population of VHE gamma-ray emitters is dominated by the pulsar wind nebula and supernova remnant source classes, although nearly a third remain unidentified or confused. The sensitivity of H.E.S.S. to sources in the inner Galaxy has improved significantly over the past two years, from continued survey observations, dedicated follow-up observations of interesting source candidates, and from the development of advanced methods for discrimination of gamma-ray-induced showers from the dominant background of hadron-induced showers. The latest maps of the Galaxy at TeV energies will be presented, and a few remarkable new sources will be highlighted.

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arXiv2011

Very-high-energy gamma radiation from supernova remnants as seen with H.E.S.S

Very-high-energy (VHE, E > 100 GeV) gamma radiation has already been detected from several supernova remnants (SNRs). These objects, which are well-studied in radio, optical and X-ray wavelengths, constitute one of the most intriguing source classes in VHE astronomy. H.E.S.S., an array of four imaging atmospheric Cherenkov telescopes in Namibia, has recorded an extensive dataset of VHE gamma-ray observations covering the central region of the Milky Way, both from pointed observations as well as from the Galactic Plane Survey conducted in the inner region of the Galaxy. From radio observations, several hundred SNRs are known in the Milky Way, but until now only few of them have been identified as VHE gamma-ray emitters. Using the H.E.S.S. dataset and a large ensemble of radio SNRs localized in the inner region of the Galaxy, the standard framework that links the origin of cosmic rays to the gamma-ray visibility of SNRs can now be tested. Here we present the ensemble of investigated SNRs and discuss constraints on the parameter space used within a theoretical model of hadronic VHE gamma-ray production.

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arXiv2011

A new analysis strategy for detection of faint gamma-ray sources with Imaging Atmospheric Cherenkov Telescopes

A new background rejection strategy for gamma-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 gamma-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.

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arXiv2008

On the evolution of the Gamma- and X-ray luminosities of Pulsar Wind Nebulae

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.

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