arXiv subjects

L. A. Tejedor

Publications and source records attributed to L. A. Tejedor.

10 recordsLinked to original sources

arXiv2025

Development of a Central Trigger Processor board for the Advanced SiPM based camera of the CTA Large-Sized Telescopes

We present ongoing work on the Central Trigger Processor board (CTPb), a trigger subsystem for the future advanced SiPM-based Large-Sized Telescope (LST) camera of the Cherenkov Telescope Array Observatory (CTAO). The camera will implement a fully digital trigger, exploiting the increased resolution to improve discrimination of low-energy $γ$-ray events from Night Sky Background noise. This approach aims to enhance telescope sensitivity while satisfying strict timing and data rate constraints. We describe the CTPb conceptual design and report initial results from hardware prototypes under evaluation within this next-generation trigger architecture.

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arXiv2023

Timing performances of NectarCAM, a Medium Sized Telescope Camera for the Cherenkov Telescope Array

NectarCAM is a Cherenkov camera that will be installed on Medium-Sized Telescopes of the northern array of the Cherenkov Telescope Array Observatory (CTAO). It is composed of 265 modules, each of which includes 7 photo-multiplier tubes, a Front-End Board and a camera trigger system for data collection. The first NectarCAM unit is currently being integrated at CEA Paris-Saclay in France. Once installed at the CTAO's northern site, the NectarCAM's timing abilities will be crucial for reducing noise in images, improving image cleaning, and distinguishing between gamma-ray photons and cosmic-ray background. Additionally, it will enable coincidence identification with neighboring telescopes for stereoscopic observations. The timing system of NectarCAM has been tested in a dark room with various light sources. The results of the tests, including timing precision and accuracy of the trigger arrival relative to a laser source, and the timing of individual and multiple pixel signals, will be presented.

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arXiv2023

The NectarCAM Timing System

NectarCAM is a Cherenkov camera which is going to equip the Medium-Sized Telescopes (MST) of the northern site of the Cherenkov Telescope Array Observatory (CTAO). NectarCAM is equipped with 265 modules, each consisting of 7 photo-multiplier tubes (PMTs), a Front-End Board and a local camera trigger system used for data acquisition. This paper addresses the timing performance of NectarCAM which are crucial to reduce the noise in shower images and improve image cleaning as well as to discriminate between gamma-ray photons and cosmic-ray background and finally to allow coincidence identification with neighbouring telescopes for stereoscopic operations. Verification tests of the system have been performed in a dark room using various light sources to illuminate the first NectarCAM unit. The resulting timing precision and accuracy of the trigger arrival relative to a laser source, of individual and multiple pixel signals have been studied and are shown to comply to CTAO requirements.

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arXiv2021

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.

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arXiv2021

Commissioning of the camera of the first Large Size Telescope of the Cherenkov Telescope Array

The first Large Size Telescope (LST-1) of the Cherenkov Telescope Array has been operational since October 2018 at La Palma, Spain. We report on the results obtained during the camera commissioning. The noise level of the readout is determined as a 0.2 p.e. level. The gain of PMTs are well equalized within 2\% variation, using the calibration flash system. The effect of the night sky background on the signal readout noise as well as the PMT gain estimation are also well evaluated. Trigger thresholds are optimized for the lowest possible gamma-ray energy threshold and the trigger distribution synchronization has been achieved within 1~ns precision. Automatic rate control realizes the stable observation with 1.5\% rate variation over 3 hours. The performance of the novel DAQ system demonstrates a less than 10\% dead time for 15 kHz trigger rate even with sophisticated online data correction.

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arXiv2019

Searching for optical and VHE counterparts of fast radio bursts with MAGIC

Fast radio bursts (FRBs) are an enigmatic class of extragalactic transients emitting Jy-level radio bursts in the GHz band, lasting for only a few ms. So far, some objects are known to repeat while several others are not, likely indicating multiple origins. There are many theoretical models, some predict prompt VHE or optical emission correlated with FRBs while others imply VHE afterglows hours after the FRB. To test these predictions and unravel the nature of FRB progenitors, the stereoscopic Imaging Atmospheric Cherenkov Telescopes (IACTs) system MAGIC has been participating in FRB observation campaigns since 2016. As IACTs are sensitive to Cherenkov photons in the UV/blue region of the electromagnetic spectrum and use photo-detectors with time response faster than a ms, MAGIC is also able to perform simultaneous optical observations through a dedicated system installed in the central PMT of its camera. The main challenge faced by MAGIC in searching for optical counterpart of FRBs is the presence of irreducible background optical events due to terrestrial sources. We present new results from MAGIC observations of the first repeating FRB 121102 during several MWL observation campaigns. The recently improved instrument and refined strategy to search for counterparts of FRBs in the VHE and optical bands will also be presented.

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arXiv2017

MAGIC sensitivity to millisecond-duration optical pulses

The MAGIC telescopes are a system of two Imaging Atmospheric Cherenkov Telescopes (IACTs) designed to observe very high energy (VHE) gamma rays above ~50 GeV. However, as IACTs are sensitive to Cherenkov light in the UV/blue and use photo-detectors with a time response well below the ms scale, MAGIC is also able to perform simultaneous optical observations. Through an alternative system installed in the central PMT of MAGIC II camera, the so-called central pixel, MAGIC is sensitive to short (1ms - 1s) optical pulses. Periodic signals from the Crab pulsar are regularly monitored. Here we report for the first time the experimental determination of the sensitivity of the central pixel to isolated 1-10 ms long optical pulses. The result of this study is relevant for searches of fast transients such as Fast Radio Bursts (FRBs).

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arXiv2013

The NectarCAM camera project

In the framework of the next generation of Cherenkov telescopes, the Cherenkov Telescope Array (CTA), NectarCAM is a camera designed for the medium size telescopes covering the central energy range of 100 GeV to 30 TeV. NectarCAM will be finely pixelated (~ 1800 pixels for a 8 degree field of view, FoV) in order to image atmospheric Cherenkov showers by measuring the charge deposited within a few nanoseconds time-window. It will have additional features like the capacity to record the full waveform with GHz sampling for every pixel and to measure event times with nanosecond accuracy. An array of a few tens of medium size telescopes, equipped with NectarCAMs, will achieve up to a factor of ten improvement in sensitivity over existing instruments in the energy range of 100 GeV to 10 TeV. The camera is made of roughly 250 independent read-out modules, each composed of seven photo-multipliers, with their associated high voltage base and control, a read-out board and a multi-service backplane board. The read-out boards use NECTAr (New Electronics for the Cherenkov Telescope Array) ASICs which have the dual functionality of analogue memories and Analogue to Digital Converter (ADC). The camera trigger to be used will be flexible so as to minimize the read-out dead-time of the NECTAr chips. We present the camera concept and the design and tests of the various subcomponents. The design includes the mechanical parts, the cooling of the electronics, the readout, the data acquisition, the trigger, the monitoring and services.

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arXiv2013

Development of the Photomultiplier-Tube Readout System for the CTA Large Size Telescope

We have developed a prototype of the photomultiplier tube (PMT) readout system for the Cherenkov Telescope Array (CTA) Large Size Telescope (LST). Two thousand PMTs along with their readout systems are arranged on the focal plane of each telescope, with one readout system per 7-PMT cluster. The Cherenkov light pulses generated by the air showers are detected by the PMTs and amplified in a compact, low noise and wide dynamic range gain block. The output of this block is then digitized at a sampling rate of the order of GHz using the Domino Ring Sampler DRS4, an analog memory ASIC developed at Paul Scherrer Institute. The sampler has 1,024 capacitors per channel and four channels are cascaded for increased depth. After a trigger is generated in the system, the charges stored in the capacitors are digitized by an external slow sampling ADC and then transmitted via Gigabit Ethernet. An onboard FPGA controls the DRS4, trigger threshold, and Ethernet transfer. In addition, the control and monitoring of the Cockcroft-Walton circuit that provides high voltage for the 7-PMT cluster are performed by the same FPGA. A prototype named Dragon has been developed that has successfully sampled PMT signals at a rate of 2 GHz, and generated single photoelectron spectra.

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arXiv2013

An Analog Trigger System for Atmospheric Cherenkov Telescopes

Arrays of Cherenkov telescopes typically use multi-level trigger schemes to keep the rate of random triggers from the night sky background low. At a first stage, individual telescopes produce a trigger signal from the pixel information in the telescope camera. The final event trigger is then formed by combining trigger signals from several telescopes. In this poster, we present a possible scheme for the Cherenkov Telescope Array telescope trigger, which is based on the analog pulse information of the pixels in a telescope camera. Advanced versions of all components of the system have been produced and working prototypes have been tested, showing a performance that meets the original specifications. Finally, issues related to integrating the trigger system in a telescope camera and in the whole array will be dealt with.

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