Ground-based Gamma-ray Astronomy Research Articles

CTC and CT5TEA: An advanced multi-channel digitizer and trigger ASIC for imaging atmospheric Cherenkov telescopes

We have developed a new set of Application-Specific Integrated Circuits (ASICs) of the TARGET family (CTC and CT5TEA), designed for the readout of signals from photosensors in cameras of Imaging Atmospheric Cherenkov Telescopes (IACTs) for ground-based gamma-ray astronomy. We present the performance and design details. Both ASICs feature 16 channels, with CTC being a Switched-Capacitor Array (SCA) sampler at 0.5 to 1GSa/s with a 16,384 sample deep storage buffer, including the functionality to digitize full waveforms at arbitrary times. CT5TEA is its companion trigger ASIC (though may be used on its own), which provides trigger information for the analog sum of four (and 16) adjacent channels. Since sampling and triggering takes place in two separate ASICs, the noise due to interference from the SCA is suppressed, and allows a minimal trigger threshold of ≤ 2.5 mV (0.74photo electrons (p.e.)) with a trigger noise of ≤ 0.5 mV (0.15p.e.). For CTC, a maximal input voltage range from −0.5V up to 1.7V is achieved with an effective bit range of > 11.6bits and a baseline noise of 0.7 mV. The cross-talk improved to ≤ 1% over the whole −3 dB bandwidth of 220MHz and even down to 0.2% for 1.5V pulses of 10 ns width. Not only is the performance presented, but a temperature-stable calibration routine for pulse mode operation is introduced and validated. The resolution is found to be ∼ 2.5% at 33.7 mV (10p.e.) and ≤ 0.3% at 337 mV (100p.e.) with an integrated non-linearity of < 1.6mV. Developed for the Small-Sized Telescope (SST) and Schwarzschild-Couder Telescope (SCT) cameras of the Cherenkov Telescope Array Observatory (CTAO), CTC and CT5TEA are deployed for both prototypes and shall be integrated into the final versions.

Ground-based gamma-ray astronomy: status and future

In this video article the author covers the history and current status of ground-based gamma-ray astronomy. The recent results in this field have brought important implications to various aspects in astrophysics, such as cosmic ray science and black holes and dark matters, and thus advanced our understanding of the dynamic non-thermal universe. The author also discusses the future prospects in this field, especially the possible imaging air Cherenkov telescopes in GeV energy range.

Application of graph networks to background rejection in Imaging Air Cherenkov Telescopes

Imaging Air Cherenkov Telescopes (IACTs) are essential to ground-based observations of gamma rays in the GeV to TeV regime. One particular challenge of ground-based gamma-ray astronomy is an effective rejection of the hadronic background.We propose a new deep-learning-based algorithm for classifying images measured using single or multiple Imaging Air Cherenkov Telescopes.We interpret the detected images as a collection of triggered sensors that can be represented by graphs and analyzed by graph convolutional networks.For images cleaned of the light from the night sky, this allows for an efficient algorithm design that bypasses the challenge of sparse images in deep learning approaches based on computer vision techniques such as convolutional neural networks. We investigate different graph network architectures and find a promising performance with improvements to previous machine-learning and deep-learning-based methods.

TAIGA - An advanced hybrid detector complex for astroparticle physics and high energy gamma-ray astronomy

The physical motivations, present status, main results in study of cosmic rays and in the field of gamma-ray astronomy as well future plans of the TAIGA-1 (Tunka Advanced Instrument for cosmic ray physics and Gamma Astronomy) project are presented. The TAIGA observatory addresses ground-based gamma-ray astronomy and astroparticle physics at energies from a few TeV to several PeV, as well as cosmic ray physics from 100 TeV to several EeV. The pilot TAIGA-1 complex is located in the Tunka valley, ~50 km west from the southern tip of the lake Baikal.

The silicon photomultiplier-based camera for the Cherenkov Telescope Array small-sized telescopes

The Cherenkov Telescope Array (CTA) is the next generation ground-based gamma-ray astronomy observatory, planned to comprise two arrays of imaging air Cherenkov telescopes (IACTs) located in the northern and southern hemispheres. Three telescope sizes are required to cover the CTA gamma-ray energy range from 20 GeV to 300 TeV. An array of several tens of Small-Sized Telescopes (SSTs) at the southern site situated in the Andes at Paranal in Chile, will provide unprecedented sensitivity above 1 TeV and up to 300 TeV, and offer the highest angular resolution of any instrument at these energies. Following a down selection from three prototype telescopes, the design finally selected for SST comprises a dual mirror Schwarzschild–Couder optic with a 4.3 m diameter primary mirror and a 1.8 m secondary mirror imaged by a silicon photomultiplier (SiPM)-based camera with a ∼9°field of view (FoV). The dual mirror optics produce a smaller plate-scale aplanatic focal plane allowing a small, low-cost camera to be employed, compared to that required for the conventional single mirror Davies-Cotton IACT design. The camera comprises an array of 2048 SiPM pixels, configured as 32 sensor and electronics modules each with an 8 × 8 pixel2 tile populated with 6 × 6 mm2 SiPM pixels. Full waveform capture on every channel is provided by the TARGET ASIC which performs the dual function of event triggering and waveform digitization of the full camera at 1 GSample/s. We describe the finalized SST camera design including its optimization for the production phase of the project anticipated to begin in 2023.

Exploring the high energy frontiers of the Milky Way with ground-based gamma-ray astronomy: PeVatrons and the quest for the origin of Galactic cosmic-rays

Cosmic rays (CRs) are charged particles that arrive at Earth isotropically from all directions and interact with the atmosphere. The presence of a spectral knee feature seen in the CR spectrum at 3 PeV energies is an evidence that astrophysical objects within our Galaxy, which are known as 'Galactic PeVatrons', are capable of accelerating particles to PeV energies. Scientists have been trying to identify the origin of Galactic CRs and have been looking for signatures of Galactic PeVatrons through neutral messengers. Recent advancements in ground-based γ-ray astronomy have led to the discovery of 12 Galactic sources emitting above 100 TeV energies, and even the first time detection of PeV photons from the direction of Crab Nebula. These groundbreaking discoveries have opened up the field of ultrahigh-energy (UHE, E>100 TeV) γ-ray astronomy, which can help us explore the high-energy frontiers of our Galaxy, hunt for PeVatron sources, and shed light on the century-old problem of the origin of CRs. This review article provides an overview of the current state of the art and potential future directions for the search for Galactic PeVatrons using ground-based γ-ray observations.

Gamma hadron separation method in ground-based gamma ray astronomy using simulated data

Gamma hadron separation method in ground-based gamma ray astronomy using simulated data

Ground-based gamma-ray astronomy: history and development of techniques

Very high energy (VHE) $$\gamma $$ -rays constitute one of the main pillars of high energy astrophysics. Gamma-rays are produced under extreme relativistic conditions in the Universe. VHE $$\gamma $$ -rays can be detected indirectly on the ground. Detection of these energetic photons poses several technological challenges. First, even though $$\gamma $$ -rays are highly penetrative, the Earth’s atmosphere is opaque to them. Second, these $$\gamma $$ -rays are to be detected against the overwhelming background of cosmic rays. When a VHE $$\gamma $$ -ray arrives at the top of the atmosphere, it produces charged secondaries. These charged particles produce Cherenkov flashes in optical band. Even though first attempts to detect these Cherenkov flashes were made almost 70 years ago, it took several decades of relentless efforts to streamline the technique. Ground-based VHE $$\gamma $$ -ray astronomy has now established itself as one of the crucial branches of conventional high energy astronomy to study the relativistic Universe. In this article, we look back and present a historical perspective followed by a discussion on the current status and finally what lays ahead.

35 Years of Ground-Based Gamma-ray Astronomy

This paper provides a brief, personal account of the development of ground-based gamma-ray astronomy, primarily over the last 35 years, with some digressions into the earlier history of the field. Ideas related to the imaging of Cherenkov events and the potential for the use of arrays were in existence for some time before the technical expertise required for their exploitation emerged. There has been occasional controversy, great creativity and some heroic determination—all of it part of establishing a new window into the universe.

TAIGA—an advanced hybrid detector complex for astroparticle physics and high energy gamma-ray astronomy in the Tunka valley

The TAIGA observatory addresses ground-based gamma-ray astronomy at energies from a few TeV to several PeV, cosmic ray physics from 100 TeV to several EeV as well as for search for axion-like particles, Lorentz violations and another evidence of New Physics. In 2020 year a one square kilometer TAIGA setup should be put in operation.

Measurement of the Crab Nebula Spectrum Past 100 TeV with HAWC

Abstract We present TeV gamma-ray observations of the Crab Nebula, the standard reference source in ground-based gamma-ray astronomy, using data from the High Altitude Water Cherenkov (HAWC) Gamma-Ray Observatory. In this analysis we use two independent energy estimation methods that utilize extensive air shower variables such as the core position, shower angle, and shower lateral energy distribution. In contrast, the previously published HAWC energy spectrum roughly estimated the shower energy with only the number of photomultipliers triggered. This new methodology yields a much-improved energy resolution over the previous analysis and extends HAWC’s ability to accurately measure gamma-ray energies well beyond 100 TeV. The energy spectrum of the Crab Nebula is well fit to a log-parabola shape with emission up to at least 100 TeV. For the first estimator, a ground parameter that utilizes fits to the lateral distribution function to measure the charge density 40 m from the shower axis, the best-fit values are (TeV cm2 s)−1, , and . For the second estimator, a neural network that uses the charge distribution in annuli around the core and other variables, these values are (TeV cm2 s)−1, , and β = 0.06 ± 0.01 ± 0.02. The first set of uncertainties is statistical; the second set is systematic. Both methods yield compatible results. These measurements are the highest-energy observation of a gamma-ray source to date.

The future of ground-based gamma-ray astronomy

Ground-based gamma-ray astronomy is a young branch of high-energy astrophysics, addressing the highest energies in the electromagnetic spectrum. TeV photons cannot be produced by “ordinary” stars since they require quite extreme conditions, thus they allow the study of extreme astrophysical objects such as supernova remnants, neutron stars, black holes, both stellar and supermassive, as well as the elusive dark matter. To make it possible to go a step further in this exciting field, a world-wide collaboration is building the Cherenkov telescope array, an ambitious global observatory, to which the Italian community is strongly committed. The foreseen contribution of the Istituto Nazionale di Astrofisca (INAF) will be briefly outlined.

Ground-based Gamma-Ray Astronomy: an Introduction

During the last two decades Gamma-Ray Astronomy has emerged as a powerful tool to study cosmic ray physics. In fact, photons are not deviated by galactic or extragalactic magnetic fields so their directions bring the information of the production sites and are easier to detect than neutrinos. Thus the search for γ primarily address in the framework of the search of cosmic ray sources and to the investigation of the phenomena in the acceleration sites. This note is not a place for a review of ground-based gamma-ray astronomy. We will introduce the experimental techniques used to detect photons from ground in the overwhelming background of CRs and briefly describe the experiments currently in data taking or under installation.

Extending the observation limits of Imaging Air Cherenkov Telescopes toward horizon

Usually the Imaging Atmospheric Cherenkov Telescopes, used for the ground-based gamma-ray astronomy in the very high energy range 50 GeV - 50 TeV, perform air shower observations till the zenith angle of ~60 deg. Beyond that limit the column density of air increases rapidly and the Cherenkov light absorption starts playing a major role. Absence of a proper calibration method of light transmission restrained researchers performing regular measurements under zenith angles >>60 deg. We extend the observation of air showers in Cherenkov light till almost the horizon. We use an aperture photometry technique for calibrating the Cherenkov light transmission in atmosphere during observations under very large zenith angles. Along with longer in time observations of a given source, this observation technique allows one to strongly increase the collection area and the event statistics of Cherenkov telescopes for the very high energy part of the spectrum. Study of the spectra of the highest energy gamma rays from a handful of candidate sources can provide a clue for the origin of the galactic cosmic rays. We show that MAGIC very large zenith angle observations yield a collection area in excess of a square kilometer. For selected sources this is becoming comparable with the target collection area anticipated with the Cherenkov Telescope Array.

Atmospheric Electricity at Durham (27 May 2017)

Atmospheric Electricity at Durham (27 May 2017)

TAIGA experiment: present status and perspectives

The TAIGA observatory addresses ground-based gamma-ray astronomy at energies from a few TeV to several PeV, as well as cosmic ray physics from 100 TeV to several EeV . TAIGA will be located in the Tunka valley, ∼ 50 km West from Lake Baikal. The different detectors of the TAIGA will be grouped in 6 arrays to measure Cherenkov and radio emission as well as electron and muon components of atmospheric showers. The combination of the wide angle Cherenkov detectors of the TAIGA-HiSCORE array and the 4-m Imaging Atmospheric Cherenkov Telescopes of the TAIGA-IACT array with their FoV of 10×10 degrees and underground muon detectors offers a very cost effective way to construct a 5 km2 array for gamma-ray astronomy.

TARGET 5: A new multi-channel digitizer with triggering capabilities for gamma-ray atmospheric Cherenkov telescopes

TARGET 5 is a new application-specific integrated circuit (ASIC) of the TARGET family, designed for the readout of signals from photosensors in the cameras of imaging atmospheric Cherenkov telescopes (IACTs) for ground-based gamma-ray astronomy. TARGET 5 combines sampling and digitization on 16 signal channels with the formation of trigger signals based on the analog sum of groups of four channels. We describe the ASIC architecture and performance. TARGET 5 improves over the performance of the first-generation TARGET ASIC, achieving: tunable sampling frequency from <0.4 GSa/s to >1 GSa/s; a dynamic range on the data path of 1.2 V with effective dynamic range of 11 bits and DC noise of ∼0.6 mV; 3-dB bandwidth of 500 MHz; crosstalk between adjacent channels <1.3%; charge resolution improving from 40% to <4% between 3 photoelectrons (p.e.) and >100 p.e. (assuming 4 mV per p.e.); and minimum stable trigger threshold of 20 mV (5 p.e.) with trigger noise of 5 mV (1.2 p.e.), which is mostly limited by interference between trigger and sampling operations. TARGET 5 is the first ASIC of the TARGET family used in an IACT prototype, providing one development path for readout electronics in the forthcoming Cherenkov Telescope Array (CTA).

178 - An Adolescent Patient with Myelodysplastic Syndromes and Acquired Immunodeficiency: A Case Report and Literature Review

TARGET 5 is a new application-specific integrated circuit (ASIC) of the TARGET family, designed for the readout of signals from photosensors in the cameras of imaging atmospheric Cherenkov telescopes (IACTs) for ground-based gamma-ray astronomy. TARGET 5 combines sampling and digitization on 16 signal channels with the formation of trigger signals based on the analog sum of groups of four channels. We describe the ASIC architecture and performance. TARGET 5 improves over the performance of the first-generation TARGET ASIC, achieving: tunable sampling frequency from <0.4 GSa/s to >1 GSa/s; a dynamic range on the data path of 1.2 V with effective dynamic range of 11 bits and DC noise of ∼0.6 mV; 3-dB bandwidth of 500 MHz; crosstalk between adjacent channels <1.3%; charge resolution improving from 40% to <4% between 3 photoelectrons (p.e.) and >100 p.e. (assuming 4 mV per p.e.); and minimum stable trigger threshold of 20 mV (5 p.e.) with trigger noise of 5 mV (1.2 p.e.), which is mostly limited by interference between trigger and sampling operations. TARGET 5 is the first ASIC of the TARGET family used in an IACT prototype, providing one development path for readout electronics in the forthcoming Cherenkov Telescope Array (CTA).

Overview of Atmospheric Simulation Efforts in CTA

The Cherenkov Telescope Array (CTA) is an observatory for ground-based gamma-ray astronomy currently under construction, which will observe photons with very high energies (20 GeV – 300 TeV). One of the main contributions to the systematic uncertainties stems from the uncertainty on the atmospheric density profile, of molecules and aerosols. To minimize these systematics a full calibration of the atmospheric properties is important as well as a calibration of the detector response. In the paper we introduce the strategy for atmospheric simulations, use of Monte Carlo simulations and available CTA computing resources. We also describe in more detail realized and planned atmospheric simulations as well as the Czech contribution to this effort.

Parametric analysis of cherenkov light LDF from EAS for high energy gamma rays and nuclei: Ways of practical application

In this paper we propose a 'knee-like' approximation of the lateral distribution of the Cherenkov light from extensive air showers in the energy range 30-3000 TeV and study a possibility of its practical application in high energy ground-based gamma-ray astronomy experiments (in particular, in TAIGA-HiSCORE). The approximation has a very good accuracy for individual showers and can be easily simplified for practical application in the HiSCORE wide angle timing array in the condition of a limited number of triggered stations.