Development of the photomultiplier tube readout system for the first Large-Sized Telescope of the Cherenkov Telescope Array

The Cherenkov Telescope Array (CTA) is the next generation ground-based very high energy gamma-ray observatory. The Large-Sized Telescope (LST) of CTA targets 20 GeV -- 1 TeV gamma rays and has 1855 photomultiplier tubes (PMTs) installed in the focal plane camera. With the 23 m mirror dish, the night sky background (NSB) rate amounts to several hundreds MHz per pixel. In order to record clean images of gamma-ray showers with minimal NSB contamination, a fast sampling of the signal waveform is required so that the signal integration time can be as short as the Cherenkov light flash duration (a few ns). We have developed a readout board which samples waveforms of seven PMTs per board at a GHz rate. Since a GHz FADC has a high power consumption, leading to large heat dissipation, we adopted the analog memory ASIC "DRS4". The sampler has 1024 capacitors per channel and can sample the waveform at a GHz rate. Four channels of a chip are cascaded to obtain deeper sampling depth with 4096 capacitors. After a trigger is generated in a mezzanine on the board, the waveform stored in the capacitor array is subsequently digitized with a low speed (33 MHz) ADC and transferred via the FPGA-based Gigabit Ethernet to a data acquisition system. Both a low power consumption (2.64 W per channel) and high speed sampling with a bandwidth of $>$300 MHz have been achieved. In addition, in order to increase the dynamic range of the readout we adopted a two gain system achieving from 0.2 up to 2000 photoelectrons in total. We finalized the board design for the first LST and proceeded to mass production. Performance of produced boards are being checked with a series of quality control (QC) tests. We report the readout board specifications and QC results.Comment: In Proceedings of the 34th International Cosmic Ray Conference (ICRC2015), The Hague, The Netherlands. All CTA contributions at arXiv:1508.0589

MAGIC and H.E.S.S. detect VHE gamma rays from the blazar OT081 for the first time: a deep multiwavelength study

https://pos.sissa.it/395/815/pdfPublished versio

Algoritmi paralleli di trigger per decadimenti adronici di mesoni B nellâesperimento LHCb al CERN

L'esperimento LHCb studia la Fisica del Sapore tramite l'osservazione dei decadimenti di diversi tipi di mesoni B prodotti nelle collisioni di protoni all'acceleratore LHC del CERN. Dal 2015 l'energia dei protoni e l'intensità dei fasci dell'LHC saranno gradualmente aumentati per permettere ricerche di "Fisica Nuova", oltre il Modello Standard delle particelle elementari. Per sostenere e sfruttare adeguatamente in LHCb le elevate luminosità sarà necessario costruire una nuova elettronica di Front-End per i rivelatori ed un nuovo sistema di Trigger, Read-Out e acquisizione dati. Il disegno dell'innovativo sistema di trigger di LHCb-Upgrade prevede che fin dal livello più basso di trigger la ricostruzione degli eventi sia affidata non ad hardware ad-hoc ma a sistemi basati su processori commerciali, come ad esempio le CPU dei normali PC. Dato l'enorme flusso dei dati da processare (~5TB/s) e per evitare l'impiego di farm di PC troppo grandi il gruppo LHCb-Padova ha proposto l'impiego di architetture multi/many-cores. Il lavoro proposto per questa tesi di laurea si colloca nell'ambito di tale "Upgrade" dell'esperimento LHCb e riguarda la realizzazione di un nuovo trigger che permetta la ricostruzione in tempo reale di tracce e vertici dai dati dei tracciatori di silicio LHCb e la selezione con alta efficienza di decadimenti di mesoni B, in particolare di tipo adronico. Il nuovo trigger sarà sviluppato utilizzando processori grafici (GPU) commerciali caratterizzati da enormi capacità di calcolo e rapidità di trasferimento dati da/verso la memoria (GRAM). La tesi dovrà affrontare principalmente i seguenti temi: (1) lo studio ed il confronto di diversi nuovi algoritmi paralleli per la ricostruzione di tracce e vertici nei tracciatori a silicio e per la selezione degli eventi di interesse; (2) l'ottimizzazione dell'impacchettamento dei dati e del loro trasferimento rapido da/verso la GPU. Nello sviluppo degli algoritmi di trigger particolare attenzione sarà posta per il canale con violazione di CP Bs-> psi(KK) psi(KK) che costituirà per LHCb-Upgrade una delle principali sonde per la fisica oltre il Modello Standard. Il lavoro della tesi potrà essere utilizzato non solo durante la fase di presa dati con altissima intensità (dal 2018) ma già fin dal 2015 quando LHC riprenderà a fornire collisioni di protoni ad elevate energie e moderate intensità. Si prevede infatti che mentre la nuova elettronica di LHCb-Upgrade sarà installata dal 2018, il nuovo trigger basato su GPU potrà essere utilizzato come trigger di alto livello in LHCb già dal 2015. Durante il lavoro di tesi sarà possibile ed utile collaborare nell'ambito del gruppo di lavoro per lo sviluppo del trigger di LHCb, in particolare trascorrendo alcuni periodi di lavoro presso i laboratori del CERN

The CTA observatory towards operation and prospects for new sources detection

This thesis work is about the Cherenkov Telescope Array (CTA). The Cherenkov Telescope Array is the next generation ground-based observatory for gamma-ray astronomy. It will consist of more than 100 Imaging Air Cherenkov Telescopes. deployed in the northern and southern hemispheres. It will enable to gain a factor of ten in sensitivity compared to current experiments. The content of this thesis consists in an introductory part, in which basic concepts about high energy astrophysics are summarized. Then the principle of operation of ground-based Cherenkov telescopes is then described, along with some details about the hardware and software subsystems. The last part deals with the study of the extragalactic population of blazar type gamma-ray sources that could be detected by an array of four Large-sized Telescopes (LST) deployed in the northern site of CTA

The Cherenkov Telescope Array view of the Galactic Center region

Among all the high-energy environments of our Galaxy, the Galactic Center (GC) region is definitely the richest. It harbors a large amount of non-thermal emitters, including the closest super-massive black hole, dense molecular clouds, regions with strong star forming activity, multiple supernova remnants and pulsar wind nebulae, arc-like radio structures, as well as the base of what may be large-scale Galactic outflows, possibly related to the Fermi Bubbles. It also contains a strong diffuse TeV gamma-ray emission along the Galactic ridge, with a disputed origin, including the presence of a possible Pevatron, unresolved sources, and an increased relevance of the diffuse sea of cosmic rays. This very rich region will be one of the key targets for the next generation ground-based observatory for gamma-ray astronomy, the Cherenkov Telescope Array (CTA). Here we review the CTA science case for the study of the GC region, and present the planned survey strategy. These observations are simulated and we assess CTA's potential to better characterize the origin and nature of a selection of gamma-ray sources in the region

Design and performance of the prototype Schwarzschild-Couder telescope camera

International audienceThe prototype Schwarzschild-Couder Telescope (pSCT) is a candidate for a medium-sized telescope in the Cherenkov Telescope Array. The pSCT is based on a dual-mirror optics design that reduces the plate scale and allows for the use of silicon photomultipliers as photodetectors. The prototype pSCT camera currently has only the central sector instrumented with 25 camera modules (1600 pixels), providing a 2.68-deg field of view (FoV). The camera electronics are based on custom TARGET (TeV array readout with GSa/s sampling and event trigger) application-specific integrated circuits. Field programmable gate arrays sample incoming signals at a gigasample per second. A single backplane provides camera-wide triggers. An upgrade of the pSCT camera that will fully populate the focal plane is in progress. This will increase the number of pixels to 11,328, the number of backplanes to 9, and the FoV to 8.04 deg. Here, we give a detailed description of the pSCT camera, including the basic concept, mechanical design, detectors, electronics, current status, and first light

The blazar TXS 0506+056 associated with a high-energy neutrino: insights into extragalactic jets and cosmic ray acceleration

International audienceA neutrino with energy ∼290 TeV, IceCube-170922A, was detected in coincidence with the BL Lac object TXS 0506+056 during enhanced gamma-ray activity, with chance coincidence being rejected at ∼3σ level. We monitored the object in the very-high-energy (VHE) band with the Major Atmospheric Gamma-ray Imaging Cherenkov (MAGIC) telescopes for ∼41 hr from 1.3 to 40.4 days after the neutrino detection. Day-timescale variability is clearly resolved. We interpret the quasi-simultaneous neutrino and broadband electromagnetic observations with a novel one-zone lepto-hadronic model, based on interactions of electrons and protons co-accelerated in the jet with external photons originating from a slow-moving plasma sheath surrounding the faster jet spine. We can reproduce the multiwavelength spectra of TXS 0506+056 with neutrino rate and energy compatible with IceCube-170922A, and with plausible values for the jet power of . The steep spectrum observed by MAGIC is concordant with internal γγ absorption above ∼100 GeV entailed by photohadronic production of a ∼290 TeV neutrino, corroborating a genuine connection between the multi-messenger signals. In contrast to previous predictions of predominantly hadronic emission from neutrino sources, the gamma-rays can be mostly ascribed to inverse Compton upscattering of external photons by accelerated electrons. The X-ray and VHE bands provide crucial constraints on the emission from both accelerated electrons and protons. We infer that the maximum energy of protons in the jet comoving frame can be in the range ∼1014 – 1018 eV

Multi-epoch monitoring of TXS 0506+056 with MAGIC and MWL partners

The measurement of an astrophysical flux of high-energy neutrinos by IceCube is an important step towards finding the long-sought sources of cosmic rays. Nevertheless, the long exposure neutrino sky map shows no significant indication of point sources so far. The real-time follow- up of neutrino events turned out to be the most successful approach in neutrino point-source searches. It brought, among others, the most compelling evidence for a neutrino point source: the flaring gamma-ray blazar TXS 0506+056 in coincidence with a single high-energy neutrino from IceCube (IceCube-170922A). The fast multiwavelength(MWL) follow-up of this alert was key for establishing this coincidence and constraining the subsequent theoretical modeling for this event. In the long run, accurate and contemporaneous MWL spectral measurements are essential ingredients in investigating the physical processes leading to particle acceleration and emission of radiation. A deeper understanding of those processes allows us to put constraints on the potential neutrino emission. Here we present the light curves and simultaneous spectral energy distributions from November 2017 till February 2021 of MAGIC and MWL monitoring of TXS 0506+056. The more than two-year-long rise and high state of the radio light curve of TXS 0506+056, which started near the time of the IceCube neutrino detection, seems to have ended, as indicated by a steep decrease in the first half of 2021. We also present the theoretical interpretation of our observations

Upper limits on the very high energy emission from GRBs observed by MAGIC

The MAGIC collaboration has developed a dedicated observational strategy to repoint rapidly towards gamma-ray bursts (GRBs). In this contribution we present the information extracted from the large sample of the GRBs observed by MAGIC from 2013 to 2019. None of these GRBs were significantly detected, and this study aims to shed light on the reasons behind those non-detections. The same strategy had led to the successful detection of two GRBs at Very High Energies (VHE, E > 100 GeV). We describe the details of the MAGIC GRB observational procedure and the general properties of each observed GRB. The lack of detection can be attributed either to unfavourable conditions or GRB intrinsic properties, such as the magnetic field’s energy density, the bulk Lorentz factor, or the emitting region’s size. For the presented sample of GRBs, we show the methods used to obtain flux upper limits in the VHE range, and propose physical implications of the non-detection of VHE emission. These results constitute an essential reference point to study the broadband emission of GRBs, and for the Cherenkov telescope community to organize future follow-ups of GRBs at VHE energies

Multi-messenger characterization of Mrk501 during historically low X-ray and gamma-ray activity

Blazars, together with other active galactic nuclei, are the most luminous persistent sources in our universe; and therefore a prime candidate for very-high-energy (>0.2 TeV, VHE) gamma-ray observations. For the two MAGIC telescopes, the Mrk501 galaxy is among the brightest observed blazars due to its proximity. We report a multi-wavelength and multi-messenger study of Mrk501 with data from 2017 to 2020, when Mrk501 showed a VHE flux typically below 10% that of the Crab Nebula. During this time, we performed three long observations with NuSTAR, which characterized the hard X-ray emission during three different low-activity flux levels. This Mrk501 dataset provided the unprecedented opportunity to study multi-wavelength variability and correlations with sensitive instruments during historically low X-ray and VHE gamma-ray emission (below 5% of the Crab Nebula flux in the VHE range), which could be considered as the baseline emission of Mrk501. We complemented the broadband spectral energy distributions (SED) of the identified historically low X-ray and VHE gamma-ray flux with data published by IceCube, in order to evaluate the potential existence of a hadronic component that is stable (or slowly variable), and less visible than the leptonic component that may dominate the emission during typical and flaring activity. In this contribution, we will also describe the evolution of the broadband SED comparing different theoretical scenarios