First Avalanche-photodiode camera test (FACT): A novel camera using G-APDs for the observation of very high-energy -rays with Cherenkov telescopes

Thirty years after the discovery of the first very-high-energy γ-ray source by the Whipple telescope, the field experienced a revolution mainly driven by the third generation of imaging atmospheric Cherenkov telescopes (IACTs). The combined use of large mirrors and the invention of the imaging technique at the Whipple telescope, stereoscopic observations, developed by the HEGRA array and the fine-grained camera, pioneered by the CAT telescope, led to a jump by a factor of more than ten in sensitivity. The advent of advanced analysis techniques led to a vast improvement in background rejection, as well as in angular and energy resolutions. Recent instruments already have to deal with a very large amount of data (petabytes), containing a large number of sources often very extended (at least within the Galactic plane) and overlapping each other, and the situation will become even more dramatic with future instruments. The first large catalogues of sources have emerged during the last decade, which required numerous, dedicated observations and developments, but also made the first population studies possible. This paper is an attempt to summarize the evolution of the field towards the building up of the source catalogues, to describe the first population studies already made possible, and to give some perspectives in the context of the upcoming, new generation of instruments.

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Very High Energy Gamma-Ray Astronomy with Ground-Based Imaging Cherenkov Telescopes

Astrophysics and Space Science Library - Frontiers of Space And Ground-Based Astronomy ◽

10.1007/978-94-011-0794-5_118 ◽

1994 ◽

pp. 705-706

Author(s):

F. A. Aharonian ◽

H. J. Völk

Keyword(s):

Gamma Ray ◽

High Energy ◽

Cherenkov Telescopes ◽

Gamma Ray Astronomy ◽

High Energy Gamma ◽

Very High Energy ◽

Energy Gamma ◽

Very High

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Gamma-ray emission in radio galaxies, from MeV to TeV

Proceedings of the International Astronomical Union ◽

10.1017/s1743921318007895 ◽

2018 ◽

Vol 14 (S342) ◽

pp. 158-166

Author(s):

Eleonora Torresi

Keyword(s):

Gamma Ray ◽

Radio Galaxies ◽

High Energy ◽

Cherenkov Telescopes ◽

New Class ◽

Very High Energy ◽

Structure Complexity ◽

The Impact ◽

Jet Structure ◽

Very High

AbstractThanks to the Fermi λ-ray satellite and the current Imaging Atmospheric Cherenkov Telescopes, radio galaxies have arisen as a new class of high- and very-high energy emitters. The favourable orientation of their jets makes radio galaxies extremely relevant in addressing important issues such as: (i) revealing the jet structure complexity; (ii) localising the emitting region(s) of high- and very-high energy radiation; (iii) understanding the physical processes producing these photons. In this review the main results on the λ-ray emission studies of radio galaxies from the MeV to TeV regimes will be presented, and the impact of future Cherenkov Telescope Array observations will be discussed.

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THE H.E.S.S. EXTRAGALACTIC SKY

International Journal of Modern Physics Conference Series ◽

10.1142/s201019451460163x ◽

2014 ◽

Vol 28 ◽

pp. 1460163

Author(s):

◽

JEAN-PHILIPPE LENAIN

Keyword(s):

Radio Galaxies ◽

High Energy ◽

Bl Lac Objects ◽

Dominant Class ◽

Cherenkov Telescopes ◽

Spectrum Radio ◽

System Experiment ◽

Very High Energy ◽

Stereoscopic System ◽

Very High

More than fifty extragalactic very high energy (VHE; E > 100 GeV) sources have been found using ground-based imaging atmospheric Cherenkov telescopes, about twenty of which have been discovered using the H.E.S.S. (High Energy Stereoscopic System) experiment based in Namibia. Even though BL Lac objects are the dominant class of VHE detected extragalactic objects, other types of sources (starburst galaxies, radio galaxies or flat spectrum radio quasars) begin to emerge. A review of the extragalactic sources studied with H.E.S.S. is given, with an emphasis on new results.

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A fast muon tagger method for Imaging Atmospheric Cherenkov Telescopes

Journal of Physics Conference Series ◽

10.1088/1742-6596/1548/1/012036 ◽

2020 ◽

Vol 1548 (1) ◽

pp. 012036

Author(s):

L Di Venere ◽

G Giavitto ◽

F Giordano ◽

R López-Coto ◽

R Pillera

Keyword(s):

Gamma Ray ◽

High Energy ◽

Silicon Photomultiplier ◽

Cherenkov Telescopes ◽

Large Size ◽

Very High Energy ◽

Energy Gamma ◽

Design Options ◽

Very High ◽

Computation Speed

Abstract The Cherenkov Telescope Array (CTA) will be the next major observatory for Very High Energy gamma-ray astronomy. Its optical throughput calibration relies on muon Cherenkov rings. This work is aimed at developing a fast and efficient muon tagger at the camera level for the CTA telescopes. A novel technique to tag muons using the capabilities of silicon photomultiplier Compact High-Energy Camera CHEC-S, one of the design options for the camera of the small size telescopes, has been developed, studying and comparing different algorithms such as circle fitting with the Taubin method, machine learning using a neural network and simple pixel counting. Their performance in terms of efficiency and computation speed was investigated using simulations with varying levels of night sky background light. The application of the best performing method to the large size telescope camera has also been studied, to improve the speed of the muon preselection.

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Observation of the Gamma-Ray Binary HESS J0632+057 with the H.E.S.S., MAGIC, and VERITAS Telescopes

The Astrophysical Journal ◽

10.3847/1538-4357/ac29b7 ◽

2021 ◽

Vol 923 (2) ◽

pp. 241

Author(s):

C. B. Adams ◽

W. Benbow ◽

A. Brill ◽

J. H. Buckley ◽

M. Capasso ◽

...

Keyword(s):

Binary Systems ◽

Gamma Ray ◽

High Energy ◽

Energy Bands ◽

X Ray ◽

Cherenkov Telescopes ◽

Orbital Cycles ◽

Very High Energy ◽

Energy Gamma ◽

Very High

Abstract The results of gamma-ray observations of the binary system HESS J0632 + 057 collected during 450 hr over 15 yr, between 2004 and 2019, are presented. Data taken with the atmospheric Cherenkov telescopes H.E.S.S., MAGIC, and VERITAS at energies above 350 GeV were used together with observations at X-ray energies obtained with Swift-XRT, Chandra, XMM-Newton, NuSTAR, and Suzaku. Some of these observations were accompanied by measurements of the Hα emission line. A significant detection of the modulation of the very high-energy gamma-ray fluxes with a period of 316.7 ± 4.4 days is reported, consistent with the period of 317.3 ± 0.7 days obtained with a refined analysis of X-ray data. The analysis of data from four orbital cycles with dense observational coverage reveals short-timescale variability, with flux-decay timescales of less than 20 days at very high energies. Flux variations observed over a timescale of several years indicate orbit-to-orbit variability. The analysis confirms the previously reported correlation of X-ray and gamma-ray emission from the system at very high significance, but cannot find any correlation of optical Hα parameters with fluxes at X-ray or gamma-ray energies in simultaneous observations. The key finding is that the emission of HESS J0632 + 057 in the X-ray and gamma-ray energy bands is highly variable on different timescales. The ratio of gamma-ray to X-ray flux shows the equality or even dominance of the gamma-ray energy range. This wealth of new data is interpreted taking into account the insufficient knowledge of the ephemeris of the system, and discussed in the context of results reported on other gamma-ray binary systems.

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H.E.S.S. detection of very high-energy γ-ray emission from the quasar PKS 0736+017

Astronomy and Astrophysics ◽

10.1051/0004-6361/201935906 ◽

2020 ◽

Vol 633 ◽

pp. A162 ◽

Cited By ~ 4

Author(s):

◽

H. Abdalla ◽

R. Adam ◽

F. Aharonian ◽

F. Ait Benkhali ◽

...

Keyword(s):

Low Frequency ◽

Lorentz Factor ◽

High Energy ◽

Spectral Energy ◽

Cherenkov Telescopes ◽

Line Region ◽

Multi Wavelength ◽

Very High Energy ◽

Optical Continuum ◽

Very High

Context. Flat-spectrum radio-quasars (FSRQs) are rarely detected at very high energies (E ≥ 100 GeV) due to their low-frequency-peaked spectral energy distributions. At present, only six FSRQs are known to emit very high-energy (VHE) photons, representing only 7% of the VHE extragalactic catalog, which is largely dominated by high-frequency-peaked BL Lacertae objects. Aims. Following the detection of MeV–GeV γ-ray flaring activity from the FSRQ PKS 0736+017 (z = 0.189) with Fermi-LAT, the H.E.S.S. array of Cherenkov telescopes triggered target-of-opportunity (ToO) observations on February 18, 2015, with the goal of studying the γ-ray emission in the VHE band. Methods. H.E.S.S. ToO observations were carried out during the nights of February 18, 19, 21, and 24, 2015. Together with Fermi-LAT, the multi-wavelength coverage of the flare includes Swift observations in soft X-ray and optical-UV bands, and optical monitoring (photometry and spectro-polarimetry) by the Steward Observatory, and the ATOM, the KAIT, and the ASAS-SN telescopes. Results. VHE emission from PKS 0736+017 was detected with H.E.S.S. only during the night of February 19, 2015. Fermi-LAT data indicate the presence of a γ-ray flare, peaking at the time of the H.E.S.S. detection, with a flux doubling timescale of around six hours. The γ-ray flare was accompanied by at least a 1 mag brightening of the non-thermal optical continuum. No simultaneous observations at longer wavelengths are available for the night of the H.E.S.S. detection. The γ-ray observations with H.E.S.S. and Fermi-LAT are used to put constraints on the location of the γ-ray emitting region during the flare: it is constrained to be just outside the radius of the broad-line region rBLR with a bulk Lorentz factor Γ ≃ 20, or at the level of the radius of the dusty torus rtorus with Γ ≃ 60. Conclusions. PKS 0736+017 is the seventh FSRQ known to emit VHE photons, and at z = 0.189 is the nearest so far. The location of the γ-ray emitting region during the flare can be tightly constrained thanks to opacity, variability, and collimation arguments.

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Search for High Energy emission from GRBs with MAGIC

Proceedings of the International Astronomical Union ◽

10.1017/s1743921317001442 ◽

2016 ◽

Vol 12 (S324) ◽

pp. 70-73

Author(s):

Alessio Berti ◽

Keyword(s):

Gamma Ray ◽

High Energy ◽

Cherenkov Telescopes ◽

Gamma Ray Imaging ◽

Very High Energy ◽

Γ Rays ◽

High Energy Emission ◽

The Universe ◽

Very High

AbstractGamma-Ray Bursts (GRBs) are the most violent explosions in the Universe, releasing a huge amount of energy in few seconds. While our understanding of the prompt and the afterglow phases has increased with Swift and Fermi, we have very few information about their High Energy (HE, E ≲ 100) emission components. This requires a ground-based experiment able to perform fast follow-up with enough sensitivity above ~ 50 GeV. The MAGIC (Major Atmospheric Gamma-ray Imaging Cherenkov) telescopes have been designed to perform fast follow-up on GRBs thanks to fast slewing movement and low energy threshold (~ 50 GeV). Since the beginning of the operations, MAGIC followed-up 89 GRBs in good observational conditions. In this contribution the MAGIC GRBs follow-up campaign and the results which could be obtained by detecting HE and Very High Energy (VHE, E ≳ 100 GeV) γ-rays from GRBs will be reviewed.

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Search for Very High-energy Emission from the Millisecond Pulsar PSR J0218+4232

The Astrophysical Journal ◽

10.3847/1538-4357/ac20d7 ◽

2021 ◽

Vol 922 (2) ◽

pp. 251

Author(s):

V. A. Acciari ◽

S. Ansoldi ◽

L. A. Antonelli ◽

A. Arbet Engels ◽

M. Artero ◽

...

Keyword(s):

High Energy ◽

Theoretical Modeling ◽

Millisecond Pulsar ◽

Large Area ◽

Telescope Array ◽

Cherenkov Telescopes ◽

Gamma Imaging ◽

Very High Energy ◽

High Energy Emission ◽

Very High

Abstract PSR J0218+4232 is one of the most energetic millisecond pulsars known and has long been considered as one of the best candidates for very high-energy (VHE; >100 GeV) γ-ray emission. Using 11.5 yr of Fermi Large Area Telescope (LAT) data between 100 MeV and 870 GeV, and ∼90 hr of Major Atmospheric Gamma Imaging Cherenkov (MAGIC) observations in the 20 GeV to 20 TeV range, we searched for the highest energy γ-ray emission from PSR J0218+4232. Based on the analysis of the LAT data, we find evidence for pulsed emission above 25 GeV, but see no evidence for emission above 100 GeV (VHE) with MAGIC. We present the results of searches for γ-ray emission, along with theoretical modeling, to interpret the lack of VHE emission. We conclude that, based on the experimental observations and theoretical modeling, it will remain extremely challenging to detect VHE emission from PSR J0218+4232 with the current generation of Imaging Atmospheric Cherenkov Telescopes, and maybe even with future ones, such as the Cherenkov Telescope Array.

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Very-high-energy Emission from Pulsars

The Astrophysical Journal ◽

10.3847/1538-4357/ac3084 ◽

2021 ◽

Vol 923 (2) ◽

pp. 194

Author(s):

Alice K. Harding ◽

Christo Venter ◽

Constantinos Kalapotharakos

Keyword(s):

High Energy ◽

Particle Energy ◽

Cherenkov Telescopes ◽

High Energy Tail ◽

Inverse Compton ◽

Very High Energy ◽

Maximum Particle ◽

High Energy Emission ◽

Very High ◽

Accelerated Particles

Abstract Air-Cherenkov telescopes have detected pulsations at energies above 50 GeV from a growing number of Fermi pulsars. These include the Crab, Vela, PSR B1706−44, and Geminga, with the first two having pulsed detections above 1 TeV. In some cases, there appears to be very-high-energy (VHE) emission that is an extension of the Fermi spectra to high energies, while in other cases, additional higher-energy spectral components that require a separate emission mechanism may be present. We present results of broadband spectral modeling using global magnetospheric fields and multiple emission mechanisms that include synchro-curvature (SC) and inverse Compton scattered (ICS) radiation from accelerated particles (primaries) and synchrotron self-Compton (SSC) emission from lower-energy pairs. Our models predict three distinct VHE components: SC from primaries whose high-energy tail can extend to 100 GeV, SSC from pairs that can extend to several TeV, and ICS from primary particles accelerated in the current sheet that scatter pair synchrotron radiation, which appears beyond 10 TeV. Our models suggest that H.E.S.S.-II and MAGIC have detected the high-energy tail of the primary SC component that produces the Fermi spectrum in Vela, Geminga, and PSR B1706−44. We argue that the ICS component peaking above 10 TeV from Vela has been seen by H.E.S.S. Detection of this emission component from the Crab and other pulsars is possible with the High Altitude Water Cherenkov Observatory and Cherenkov Telescope Array, and will directly measure the maximum particle energy in pulsars.

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