Measurement of performance of the NectarCAM photodetectors

NectarCAM is a camera for the medium-sized telescopes of the Cherenkov Telescope Array (CTA), which covers the energy range of 100 GeV to 30 TeV. The camera is equipped with 265 focal plane modules (FPMs). Each FPM comprises 7 pixels, each consisting of a photo-multiplier tube, a preamplifier, an independently controlled power supply, and a common control system. We developed a dedicated test bench to validate and qualify the industrial FPM production and to measure the performance of each FPM in a dark room before its integration in the camera. We report the measured performance of 61 FPM prototypes obtained with our experimental setup. We demonstrate that the gains of the photo multiplier tubes are stable and that pulse widths, transit time spreads, afterpulse rates and charge resolutions are within the specifications for NectarCAM.The authors are grateful for the support of the Région Occitanie and Microtec

Dip-coated screen for gain calibration and alignment of gamma-ray telescope mirrors

In this communication, we will present a dual-purpose calibration system of NectarCAM, a medium-size-telescope camera proposed for the Cherenkov Telescope Array (CTA). The device is based on a white diffuse-reflective screen mounted on an XY motorization to reach every location in the focal plane, including a parking position when not in use. The design of the system was led by the requirements to perform the mirror alignment and the study of the telescope Point Spread Function (PSF) on one side (A), and to calibrate the photodetection chains (one for each of the 1855 photomultiplier tubes) of the camera in single photoelectron mode on the other side (B). The main requirement for the calibration device consists in producing a high-reflective (> 90% between 450 nm and 700 nm) and diffusive (following Lambert's cosine law) surface for side A. The other side, B, should emit an homogeneous amount of light over the surface. To satisfy these requirements, we developed a unique screen made out of PMMA and coated with the BC-620 paint from Saint-Gobain. For single-photoelectron calibration purposes, light is produced by a pulsed light source and injected into the screen via a fishtail light guide. We studied the optimal screen shape, paint, and painting process. To do so, we produced several prototypes and compared the light output intensity over the screen surface. These studies led to the definition of a specific painting pattern that enhances the light emission uniformity over the final octagonal screen surface. After having briefly described the developed prototypes that led to the current calibration device, we will focus on the calibration system performances and will describe the dip-coating application process, which is an essential technique to achieve reliable and reproducible optical performances

Measurement of performance of the NectarCAM photodetectors

International audienc

Dip-coated screen for gain calibration and alignment of gamma-ray telescope mirrors

In this communication, we will present a dual-purpose calibration system of NectarCAM, a medium-size-telescope camera proposed for the Cherenkov Telescope Array (CTA). The device is based on a white diffuse-reflective screen mounted on an XY motorization to reach every location in the focal plane, including a parking position when not in use. The design of the system was led by the requirements to perform the mirror alignment and the study of the telescope Point Spread Function (PSF) on one side (A), and to calibrate the photodetection chains (one for each of the 1855 photomultiplier tubes) of the camera in single photoelectron mode on the other side (B). The main requirement for the calibration device consists in producing a high-reflective (> 90% between 450 nm and 700 nm) and diffusive (following Lambert's cosine law) surface for side A. The other side, B, should emit an homogeneous amount of light over the surface. To satisfy these requirements, we developed a unique screen made out of PMMA and coated with the BC-620 paint from Saint-Gobain. For single-photoelectron calibration purposes, light is produced by a pulsed light source and injected into the screen via a fishtail light guide. We studied the optimal screen shape, paint, and painting process. To do so, we produced several prototypes and compared the light output intensity over the screen surface. These studies led to the definition of a specific painting pattern that enhances the light emission uniformity over the final octagonal screen surface. After having briefly described the developed prototypes that led to the current calibration device, we will focus on the calibration system performances and will describe the dip-coating application process, which is an essential technique to achieve reliable and reproducible optical performances

Dip-coated screen for gain calibration and alignment of gamma-ray telescope mirrors

In this communication, we will present a dual-purpose calibration system of NectarCAM, a medium-size-telescope camera proposed for the Cherenkov Telescope Array (CTA). The device is based on a white diffuse-reflective screen mounted on an XY motorization to reach every location in the focal plane, including a parking position when not in use. The design of the system was led by the requirements to perform the mirror alignment and the study of the telescope Point Spread Function (PSF) on one side (A), and to calibrate the photodetection chains (one for each of the 1855 photomultiplier tubes) of the camera in single photoelectron mode on the other side (B). The main requirement for the calibration device consists in producing a high-reflective (> 90% between 450 nm and 700 nm) and diffusive (following Lambert's cosine law) surface for side A. The other side, B, should emit an homogeneous amount of light over the surface. To satisfy these requirements, we developed a unique screen made out of PMMA and coated with the BC-620 paint from Saint-Gobain. For single-photoelectron calibration purposes, light is produced by a pulsed light source and injected into the screen via a fishtail light guide. We studied the optimal screen shape, paint, and painting process. To do so, we produced several prototypes and compared the light output intensity over the screen surface. These studies led to the definition of a specific painting pattern that enhances the light emission uniformity over the final octagonal screen surface. After having briefly described the developed prototypes that led to the current calibration device, we will focus on the calibration system performances and will describe the dip-coating application process, which is an essential technique to achieve reliable and reproducible optical performances

Dip-coated screen for gain calibration and alignment of gamma-ray telescope mirrors

In this communication, we will present a dual-purpose calibration system of NectarCAM, a medium-size-telescope camera proposed for the Cherenkov Telescope Array (CTA). The device is based on a white diffuse-reflective screen mounted on an XY motorization to reach every location in the focal plane, including a parking position when not in use. The design of the system was led by the requirements to perform the mirror alignment and the study of the telescope Point Spread Function (PSF) on one side (A), and to calibrate the photodetection chains (one for each of the 1855 photomultiplier tubes) of the camera in single photoelectron mode on the other side (B). The main requirement for the calibration device consists in producing a high-reflective (> 90% between 450 nm and 700 nm) and diffusive (following Lambert's cosine law) surface for side A. The other side, B, should emit an homogeneous amount of light over the surface. To satisfy these requirements, we developed a unique screen made out of PMMA and coated with the BC-620 paint from Saint-Gobain. For single-photoelectron calibration purposes, light is produced by a pulsed light source and injected into the screen via a fishtail light guide. We studied the optimal screen shape, paint, and painting process. To do so, we produced several prototypes and compared the light output intensity over the screen surface. These studies led to the definition of a specific painting pattern that enhances the light emission uniformity over the final octagonal screen surface. After having briefly described the developed prototypes that led to the current calibration device, we will focus on the calibration system performances and will describe the dip-coating application process, which is an essential technique to achieve reliable and reproducible optical performances

CTA – the World’s largest ground-based gamma-ray observatory

International audienc

Prospects for a survey of the Galactic plane with the Cherenkov Telescope Array

International audienceApproximately one hundred sources of very-high-energy (VHE) gamma rays are known in the Milky Way. A survey of the entire Galactic Plane in the energy range from a few tens of GeV to a few hundred TeV has been proposed as a Key Science Project for the upcoming Cherenkov Telescope Array Observatory (CTAO). This article presents the status of the studies towards the Galactic Plane Survey (GPS). We build and make publicly available a sky model that combines data from observations of known gamma-ray emitters with state-of-the-art physically-driven models of synthetic populations of the main classes of established Galactic VHE sources, as well as of interstellar emission from cosmic-ray interactions in the Milky Way. We also perform an optimisation of the observation strategy. We use the improved sky model and observation strategy to simulate GPS data that are analysed using the methods and software tools under development for real data. We show that the GPS has the potential to increase the number of known Galactic VHE emitters by almost a factor of five. This corresponds to the detection of more than two hundred pulsar wind nebulae and a few tens of supernova remnants at average integral fluxes one order of magnitude lower than in the existing sample above 1 TeV, therefore opening the possibility to perform unprecedented population studies. The GPS also has the potential to provide new VHE detections of binary systems and pulsars, and to identify any bright PeVatrons. Furthermore, the GPS will constitute a pathfinder for deeper follow-up observations of these source classes. Finally, we show that we can extract from GPS data an estimate of the contribution to diffuse emission from unresolved sources, and that there are good prospects of detecting interstellar emission and statistically distinguishing different scenarios. (Abridged

Searching for very-high-energy electromagnetic counterparts to gravitational-wave events with the Cherenkov Telescope Array

The detection of electromagnetic (EM) emission following the gravitational wave (GW) event GW170817 opened the era of multi-messenger astronomy with GWs and provided the first direct evidence that at least a fraction of binary neutron star (BNS) mergers are progenitors of short Gamma-Ray Bursts (GRBs). GRBs are also expected to emit very-high energy (VHE, > 100 GeV) photons, as proven by the recent MAGIC and H.E.S.S. observations. One of the challenges for future multi-messenger observations will be the detection of such VHE emission from GRBs in association with GWs. In the next years, the Cherenkov Telescope Array (CTA) will be a key instrument for the EM follow-up of GW events in the VHE range, owing to its unprecedented sensitivity, rapid response, and capability to monitor a large sky area via scan-mode operation. We present the CTA GW follow-up program, with a focus on the searches for short GRBs possibly associated with BNS mergers. We investigate the possible observational strategies and we outline the prospects for the detection of VHE EM counterparts to transient GW events

Prospects for a survey of the Galactic plane with the Cherenkov Telescope Array

International audienceApproximately one hundred sources of very-high-energy (VHE) gamma rays are known in the Milky Way. A survey of the entire Galactic Plane in the energy range from a few tens of GeV to a few hundred TeV has been proposed as a Key Science Project for the upcoming Cherenkov Telescope Array Observatory (CTAO). This article presents the status of the studies towards the Galactic Plane Survey (GPS). We build and make publicly available a sky model that combines data from observations of known gamma-ray emitters with state-of-the-art physically-driven models of synthetic populations of the main classes of established Galactic VHE sources, as well as of interstellar emission from cosmic-ray interactions in the Milky Way. We also perform an optimisation of the observation strategy. We use the improved sky model and observation strategy to simulate GPS data that are analysed using the methods and software tools under development for real data. We show that the GPS has the potential to increase the number of known Galactic VHE emitters by almost a factor of five. This corresponds to the detection of more than two hundred pulsar wind nebulae and a few tens of supernova remnants at average integral fluxes one order of magnitude lower than in the existing sample above 1 TeV, therefore opening the possibility to perform unprecedented population studies. The GPS also has the potential to provide new VHE detections of binary systems and pulsars, and to identify any bright PeVatrons. Furthermore, the GPS will constitute a pathfinder for deeper follow-up observations of these source classes. Finally, we show that we can extract from GPS data an estimate of the contribution to diffuse emission from unresolved sources, and that there are good prospects of detecting interstellar emission and statistically distinguishing different scenarios. (Abridged