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# TeV Review Papers

#### Ground-based Gamma-Ray Astronomy: an Introduction Di Sciascio, G. (2019)

Abstract: 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 $\gamma$ 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.

#### Gamma-Ray Astrophysics de Angelis & Mallamaci (2018)

Abstract: High-energy photons are a powerful probe for astrophysics and for fundamental physics in extreme conditions. During the recent years, our knowledge of the most violent phenomena in the Universe has impressively progressed thanks to the advent of new detectors for gamma rays, both at ground and on satellites. This article reviews the present status of high-energy gamma-ray astrophysics, with emphasis on the recent results and a look to the future.

#### Status of ground based gamma-ray observations Park, N. (2017)

Abstract: This is a proceeding of a rapporteur talk given on ground-based gamma-ray astronomy at the 35th International Cosmic-Ray Conference (ICRC) held in 2017 in Busan, Republic of Korea. A total of ~300 contributions were presented during the ICRC over 17 gamma-ray sessions. Here, I summarize the contributions mainly focusing on the source observations performed by ground-based gamma-ray instruments and the connection between gamma rays and cosmic rays. Any such summary must necessarily be incomplete. However, I have attempted to provide a glance into recent progress that has been made in using ground-based gamma-ray observations to understand the nature of high energy particles in our Universe.

#### Highlights from TeV Extragalactic Sources Prandini, E. (2017)

Abstract: The number of discovered TeV sources populating the extragalactic sky in 2017 is nearly 70, mostly blazars located up to a redshift ~1. Ten years ago, in 2007, less than 20 TeV emitters were known, up to a maximum redshift of 0.2. This is a major achievement of current generation of Cherenkov telescopes operating in synergy with optical, X-ray, and GeV gamma-ray telescopes. A review of selected results from the extragalactic TeV sky is presented, with particular emphasis on recently detected distant sources.

#### TeV Astrophysics: Probing the Relativistic Universe Barres de Almeida, U. (2017)

Abstract: We focus our contribution to this volume on the relativistic Universe and on present and future experimental efforts in Teraelectronvolt Astronomy, i.e., the observation of cosmic gamma-ray photons above 100 GeV, employing ground-based imaging atmospheric Cherenkov telescopes. The main topics of our contribution are directed to the discussion of the importance of TeV observations for a better understanding of the cosmic-ray content of the galaxy and of the Universe’s most energetic astrophysical objects. In particular, we are concerned with cosmic ray accelerators: supernova remnants, pulsars and their environments, active galaxies and black holes in general. In perspective, we will briefly discuss the role of the Cherenkov Telescope Array (CTA) in the current revolution that astroparticle physics is undergoing, emphasising the key position occupied by South America in this context. The 21st Century promises to be a golden age for astroparticle physics, and it is expected that much of the frontier research in relativistic astrophysics in next decades will be associated to advances in this growing field of observational astronomy.

#### Introduction to high-energy gamma-ray astronomy Degrange, B. & Fontaine, G. (2016)

Abstract: The present issue is the first of a two-volume review devoted to gamma-ray astronomy above 100 MeV, which has witnessed considerable progress over the last 20 years. The motivations for research in this area are explained, the follow-on articles of these two issues are introduced and a brief history of the field is given.

#### Ground-based detectors in very-high-energy gamma-ray astronomy de Naurois, M. & Mazin, D. (2015)

Abstract: Following the discovery of the cosmic rays by Victor Hess in 1912, more than 70 years and numerous technological developments were needed before an unambiguous detection of the first very-high-energy gamma-ray source in 1989 was made. Since this discovery the field on very-high-energy gamma-ray astronomy experienced a true revolution: A second, then a third generation of instruments were built, observing the atmospheric cascades from the ground, either through the atmospheric Cherenkov light they comprise, or via the direct detection of the charged particles they carry. Present arrays, 100 times more sensitive than the pioneering experiments, have detected a large number of astrophysical sources of various types, thus opening a new window on the non-thermal Universe. New, even more sensitive instruments are currently being built; these will allow us to explore further this fascinating domain. In this article we describe the detection techniques, the history of the field and the prospects for the future of ground-based very-high-energy gamma-ray astronomy.

#### Atmospheric Cherenkov Gamma-ray Telescopes Holder, J. (2015)

Abstract: The stereoscopic imaging atmospheric Cherenkov technique, developed in the 1980s and 1990s, is now used by a number of existing and planned gamma-ray observatories around the world. It provides the most sensitive view of the very high energy gamma-ray sky (above 30 GeV), coupled with relatively good angular and spectral resolution over a wide field-of-view. This Chapter summarizes the details of the technique, including descriptions of the telescope optical systems and cameras, as well as the most common approaches to data analysis and gamma-ray reconstruction.

#### Status of ground-based gamma-ray astronomy Lemoine-Goumard, M. (2015)

Abstract: This article is the write-up of a rapporteur talk given at the 34th ICRC in The Hague, Netherlands. It attempts to review the results and developments presented at the conference and associated to the vibrant field of ground-based gamma-ray astronomy. In total, it aims to give an overview of the 19 gamma-ray sessions, 84 talks and 176 posters presented at the 34th ICRC on this topic. New technical advances and projects will be described with an emphasis given on the cosmic-ray related studies of the Universe.

#### The Very High Energy Sky from ~20 GeV to Hundreds of TeV - Selected Highlights de Naurois, M. (2015)

Abstract: After nearly a decade of operation, the three major arrays of atmospheric Cherenkov telescopes have revolutionized our view of the Very High Energy Universe, unveiling more than 100 sources of various types. MAGIC, consisting of two 17 m diameter telescopes on the Canary island of La Palma, and VERITAS, with four 12 m telescopes installed in southern Arizona, USA, have primarily explored the extragalactic sky, where the majority of the sources are active galactic nuclei (AGN), with gamma-ray emission originating in their relativistic jets. ...... Highlights of these observations with H.E.S.S., MAGIC and VERITAS have been presented and discussed at the conference.

#### Space- and Ground-Based Gamma-Ray Astrophysics Funk, S. (2015)

Abstract: In recent years, observational gamma-ray astronomy has seen a remarkable range of exciting new results in the high-energy and very-high energy regimes. Coupled with extensive theoretical and phenomenological studies of non-thermal processes in the Universe these observations have provided a deep insight into a number of fundamental problems of high energy astrophysics and astroparticle physics. Although the main moti- vations of gamma-ray astronomy remain unchanged, recent observational results have contributed significantly towards our understanding of many related phenomena. This article aims to review the most important results in the young and rapidly developing field of gamma-ray astrophysics.

#### Ground-Based Gamma Ray Astronomy Holder, J. (2014)

Abstract: This paper is the write-up of a rapporteur talk given by the author at the 33rd International Cosmic Ray Conference in Rio de Janeiro, Brazil, in 2013. It attempts to summarize results and developments in ground-based gamma-ray observations and instrumentation from among the ˜300 submissions to the gamma-ray sessions of the meeting. Satellite observations and theoretical developments were covered by a companion rapporteur (Stawarz, L., 33rd ICRC, Rio de Janeiro, Brazil, Rapporteur talk: Space-based Gamma-Ray Astronomy, 2013). Any review of this nature is unavoidably subjective and incomplete. Nevertheless, the article should provide a useful status report for those seeking an overview of this exciting and fast-moving field.

#### High energy astrophysics Zhang, B. & Meszaros, P. (2014)

Abstract: High energy astrophysics is one of the most active branches in the contemporary astrophysics. It studies astrophysical objects that emit X-ray and γ-ray photons, such as accreting super-massive and stellar-size black holes, and various species of neutron stars. With the operations of many space-borne and ground-based observational facilities, high energy astrophysics has enjoyed rapid development in the past decades. It is foreseen that the field will continue to advance rapidly in the coming decade, with possible ground-breaking discoveries of astrophysical sources in the high-energy neutrino and gravitational wave channels. This Special Issue of Frontiers of Physics is dedicated to a systematic survey of the field of high energy astrophysics as it stands in 2013.

#### Evolution of ground-based gamma-ray astronomy from the early days to the Cherenkov Telescope Arrays Hillas, A. M. (2013)

Abstract: Most of what we know of cosmic gamma rays has come from spacecraft, but at energies above tens of GeV it has become possible to make observations with ground-based detectors of enormously greater collecting area. In recent years one such detector type, the cluster of imaging air Cherenkov telescopes, has reached a very productive state, whilst several alternative approaches have been explored, including converted solar power collectors and novel high-altitude particle shower detectors which promised to extend the energy range covered. Key examples of development from 1952 to 2011 are followed, noting the problems and discoveries that stimulated the current work, explaining the logic of the alternative approaches that were taken. The merits of the current major Cherenkov observatories and of other viable detectors are examined and compared, with examples of the astrophysical information they are beginning to provide. The detectors are still evolving, as we still do not understand the processes onto which the gamma rays provide a window. These include the acceleration of Galactic cosmic rays (in particular, the wide-band spectra of radiation from some individual supernova remnants are still hard to interpret), the highly relativistic and variable jets from active galactic nuclei, and aspects of the electrodynamics of pulsars. Larger groups of Cherenkov telescopes still offer the possibility of an increase in power of the technique for resolvable Galactic sources especially.

#### TeV Astronomy Riger, F. M., de Ona-Wilhelmi, E. & Aharonian, F. A. (2013)

Abstract: With the successful realization of the current-generation of ground-based detectors, TeV Astronomy has entered into a new era. We review recent advances in VHE astronomy, focusing on the potential of Imaging Atmospheric Cherenkov Telescopes (IACTs), and highlight astrophysical implications of the results obtained within recent years.

#### Experimental Gamma-Ray Astronomy Paneque, D. (2012)

Abstract: Our knowledge of the gamma-ray sky has dramatically changed due to the advent of the new ground-based Imaging Atmospheric Cherenkov Telescopes (H.E.S.S., MAGIC and VERITAS) and the satellite-borne instruments (AGILE and Fermi). These facilities boosted the number of gamma-ray sources by one order of magnitude in the last 6 years, providing us with about 2000 sources detected above 100 MeV (from space) and about 100 sources detected above 100 GeV (from the ground). The combination of this large leap in experimental capabilities together with the fact that the Universe is still quite unexplored at these extreme energies is evidence of a large scientific discovery potential that will surely make the decade 2010-2020 a golden age for gamma-ray astronomy. In this manuscript I provide a subjective review of some of the most exciting observations from this rapidly evolving field during the last two years.

#### The status of gamma-ray astronomy Funk, S. (2012)

Abstract: Gamma-ray studies are an essential tool in our search for the origin of cosmic rays. Instruments like the Fermi-LAT, H.E.S.S., MAGIC and VERITAS have revolutionized our understanding of the high energy Universe. This paper describes the status of the very rich field of gamma-ray astrophysics that contains a wealth of data on Galactic and extragalactic particle accelerators. It is the write-up of a rapporteur talk given at the 32nd ICRC in Beijing, China in which new results were presented with an emphasis on the cosmic-ray related studies of the Universe.

#### TeV Gamma-ray Astronomy: A Summary Holder, J. (2012)

Abstract: The field of TeV gamma-ray astronomy has produced many exciting results over the last decade. Both the source catalogue, and the range of astrophysical questions which can be addressed, continue to expand. This article presents a topical review of the field, with a focus on the observational results of the imaging atmospheric Cherenkov telescope arrays. The results encompass pulsars and their nebulae, supernova remnants, gamma-ray binary systems, star forming regions and starburst and active galaxies.

#### The Galactic Sky seen by H.E.S.S de Naurois, M. for the H.E.S.S. collaboration (2011)

Abstract: The H.E.S.S. experiment is an array of four imaging Cherenkov telescopes located in the Khomas Highlands of Namibia. It has been operating in its full configuration since December 2003 and detects very-high-energy (VHE) gamma rays ranging from 100 GeV to 50 TeV. Since 2004, the continuous observation of the Galactic Plane by the H.E.S.S. array of telescopes has yielded the discovery of more than 50 sources, belonging to the classes of pulsar wind nebulae (PWN), supernova remnants (SNR), gamma ray binaries and, more recently, a stellar cluster and molecular clouds in the vicinity of shell-type SNRs. Galactic emission seen by H.E.S.S. and its implications for particle acceleration in our Galaxy are discussed.

#### Physics and astrophysics with gamma-ray telescopes Vandenbroucke, J. for the Fermi LAT collaboration (2010)

Abstract: In the past few years gamma-ray astronomy has entered a golden age. A modern suite of telescopes is now scanning the sky over both hemispheres and over six orders of magnitude in energy. At ~TeV energies, only a handful of sources were known a decade ago, but the current generation of ground-based imaging atmospheric Cherenkov telescopes (H.E.S.S., MAGIC, and VERITAS) has increased this number to nearly one hundred. With a large field of view and duty cycle, the Tibet and Milagro air shower detectors have demonstrated the promise of the direct particle detection technique for TeV gamma rays. At ~GeV energies, the Fermi Gamma-ray Space Telescope has increased the number of known sources by nearly an order of magnitude in its first year of operation. New classes of sources that were previously theorized to be gamma-ray emitters have now been confirmed observationally. Moreover, there have been surprise discoveries of GeV gamma-ray emission from source classes for which no theory predicted it was possible. In addition to elucidating the processes of high-energy astrophysics, gamma-ray telescopes are making essential contributions to fundamental physics topics including quantum gravity, gravitational waves, and dark matter. I summarize the current census of astrophysical gamma-ray sources, highlight some recent discoveries relevant to fundamental physics, and describe the synergetic connections between gamma-ray and neutrino astronomy. This is a brief overview intended in particular for particle physicists and neutrino astronomers, based on a presentation at the Neutrino 2010 conference in Athens, Greece. I focus in particular on results from Fermi (which was launched soon after Neutrino 2008), and conclude with a description of the next generation of instruments, namely HAWC and the Cherenkov Telescope Array.

#### Teraelectronvolt Astronomy Hinton, J. A. & Hoffman, W. (2009)

Abstract: Ground-based gamma-ray astronomy, which provides access to the TeV energy range, is a young and rapidly developing discipline. Recent discoveries in this waveband have important consequences for a wide range of topics in astrophysics and astroparticle physics. This article is an attempt to review the experimental status of this field and to provide the basic formulae and concepts required to begin the interpretation of TeV observations.

#### Gamma-ray astronomy in the summer of 2009 Torres, D. F. (2009)

Abstract: This paper presents a snapshot of the field of gamma-ray astrophysics in the early summer of 2009, as it was discussed in about 200 presentations at the International Cosmic Ray Conference (ICRC) held in Lodz, Poland. This is the written wrap up of a Rapporteur, one-hour talk and as such it is thus an atypical review, a still picture in a moment of great advancement in an observationally driven field, led by the full operation of ground-based arrays and the launch and operations of Fermi and Agile.

#### Latest results on Galactic sources as seen in VHE gamma-rays Renaud, M. (2009)

Abstract: As of early 2009, latest results on Galactic sources (mainly shell-type and plerionic supernova remnants), as observed in the very-high-energy gamma-ray domain, are reviewed. A particular attention is given to those obtained with the H.E.S.S experiment during its Galactic Plane Survey which now covers the inner part of the Milky Way. From the well identified gamma-ray sources to those without any obvious counterpart and the putative Galactic diffuse emission, this observational window fully deserves to be celebrated during this International Year of Astronomy, as a new mean to image the Galaxy and reveal sites of particle acceleration, potentially at the origin of Galactic cosmic rays.

#### Imaging Very High Energy Gamma-Ray Telescopes Voelk, H. J. and Bernloehr, K. (2008)

Abstract: The technique of gamma-ray astronomy at very high energies (VHE: > 100 GeV) with ground-based imaging atmospheric Cherenkov telescopes is described, the H.E.S.S. array in Namibia serving as example. Mainly a discussion of the physical principles of the atmospheric Cherenkov technique is given, emphasizing its rapid development during the last decade. The present status is illustrated by two examples: the spectral and morphological characterization in VHE gamma-rays of a shell-type supernova remnant together with its theoretical interpretation, and the results of a survey of the Galactic Plane that shows a large variety of non-thermal sources. The final part is devoted to an overview of the ongoing and future instrumental developments.

#### TeV Gamma-ray Astronomy: The Story So Far Weekes, T. C. (2008)

Abstract: A snapshot is presented of the present status of our knowledge of the TeV gamma-ray universe. Emphasis is put on observations made using the imaging atmospheric Cherenkov technique. The capabilities of the present generation of telescopes is listed. Progress has been dramatic and several features have been different from what was anticipated. The catalog of sources includes some 78 objects and these are tabulated as extragalactic sources (24), supernovae remnants (11), pulsar wind nebulae (10), binaries (4), miscellaneous (9), diffuse high energy sources (3) and unidentified sources (20). Some comments are made on the factors influencing the past and future development of the field.

#### Gamma Ray Astronomy and the Origin of Galactic Cosmic Rays Gabici, S. (2008)

Abstract: Diffusive shock acceleration operating at expanding supernova remnant shells is by far the most popular model for the origin of galactic cosmic rays. Despite the general consensus received by this model, an unambiguous and conclusive proof of the supernova remnant hypothesis is still missing. In this context, the recent developments in gamma ray astronomy provide us with precious insights into the problem of the origin of galactic cosmic rays, since production of gamma rays is expected both during the acceleration of cosmic rays at supernova remnant shocks and during their subsequent propagation in the interstellar medium. In particular, the recent detection of a number of supernova remnants at TeV energies nicely fits with the model, but it still does not constitute a conclusive proof of it, mainly due to the difficulty of disentangling the hadronic and leptonic contributions to the observed gamma ray emission. In this paper, the most relevant cosmic-ray-related results of gamma ray astronomy are briefly summarized, and the foreseeable contribution of future gamma ray observations to the final solution of the problem of cosmic ray origin is discussed.

#### Gamma ray astrophysics: the EGRET results Thompson, D. J. (2008)

Abstract: Cosmic gamma rays provide insight into some of the most dynamic processes in the Universe. At the dawn of a new generation of gamma-ray telescopes, this review summarizes results from the Energetic Gamma Ray Experiment Telescope (EGRET) on the Compton Gamma Ray Observatory, the principal predecessor mission studying high-energy photons in the 100 MeV energy range. EGRET viewed a gamma-ray sky dominated by prominent emission from the Milky Way, but featuring an array of other sources, including quasars, pulsars, gamma-ray bursts, and many sources that remain unidentified. A central feature of the EGRET results was the high degree of variability seen in many gamma-ray sources, indicative of the powerful forces at work in objects visible to gamma-ray telescopes.

#### The Status and future of ground-based TeV gamma-ray astronomy. A White Paper prepared for the Division of Astrophysics of the American Physical Society Buckley, J. H. (2008)

Abstract: In recent years, ground-based TeV gamma-ray observatories have made spectacular discoveries including imaging spectroscopy observations of galactic sources of different classes, and the discovery of rapid gamma-ray flares from radio galaxies and active galactic nuclei containing supermassive black holes. These discoveries, and the fact that gamma-ray astronomy has the potential to map the radiation from dark matter annihilation in our Galaxy and in extragalactic systems, have attracted the attention of the wider scientific community. The Division of Astrophysics of the American Physical Society requested the preparation of a white paper on the status and future of ground-based gamma-ray astronomy to define the science goals of a future observatory, to determine the performance specifications, to identify the areas of necessary technology development, and to lay out a clear path for proceeding beyond the near term. The white paper was written with broad community input, including discussions on several dedicated open meetings, and a number of APS or other conferences. It contains an executive summary, detailed reports from the science working groups, and appendices with supplementary material including the full author lists for the different sections of the white paper and a glossary.

#### High energy astrophysics with ground-based gamma ray detectors Aharonian, F., Buckley, J., Kifune, T. and Sinnis, G. (2008)

Abstract: Recent advances in ground-based gamma ray astronomy have led to the discovery of more than 70 sources of very high energy (E >= 100 GeV) gamma rays, falling into a number of source populations including pulsar wind nebulae, shell type supernova remnants, Wolf-Rayet stars, giant molecular clouds, binary systems, the Galactic Center, active galactic nuclei and 'dark' (yet unidentified) galactic objects. We summarize the history of TeV gamma ray astronomy up to the current status of the field including a description of experimental techniques and highlight recent astrophysical results. We also discuss the potential of ground-based gamma ray astronomy for future discoveries and describe possible directions for future instrumental developments.

#### High-(Energy)-Lights -- The Very High Energy Gamma-Ray Sky Horns, D. (2008)

Abstract: The high-lights of ground-based very-high-energy (VHE, E>100 GeV) gamma-ray astronomy are reviewed. The summary covers both Galactic and extra-galactic sources. A total of at least 70 sources are currently known. Implications for our understanding of the non-thermal Universe are discussed. The next generation of ground based gamma-ray instruments aims to cover the entire accessible energy range from as low as ~10 GeV up to 10e5 GeV and to improve the sensitivity by an order of magnitude in comparison with current instruments.

#### Recent Topics on Very High Energy Gamma-ray Astronomy Mori, M. (2008)

Abstract: With the advent of imaging atmospheric Cherenkov telescopes in late 1980's, ground-based observation of TeV gamma-rays came into reality after struggling trials by pioneers for twenty years, and the number of gamma-ray sources detected at TeV energies has increased to be over seventy now. In this review, recent findings from ground-based very-high-energy gamma-ray observations are summarized (as of 2008 March), and up-to-date problems in this research field are presented.

#### High energy astrophysics with ground-based gamma ray detectors Aharonian, F., Buckley, J., Kifune T. & Sinnis, G. (2008)

Abstract: Recent advances in ground-based gamma ray astronomy have led to the discovery of more than 70 sources of very high energy (Eγ >= 100 GeV) gamma rays, falling into a number of source populations including pulsar wind nebulae, shell type supernova remnants, Wolf-Rayet stars, giant molecular clouds, binary systems, the Galactic Center, active galactic nuclei and 'dark' (yet unidentified) galactic objects. We summarize the history of TeV gamma ray astronomy up to the current status of the field including a description of experimental techniques and highlight recent astrophysical results. We also discuss the potential of ground-based gamma ray astronomy for future discoveries and describe possible directions for future instrumental developments.

#### Status of Very High Energy gamma-ray Astronomy as of early 2008 Djannati-Atai, A. (2008)

Abstract: Data obtained in the very high energy gamma-ray band with the new generation of imaging telescopes, in particular through the galactic plane survey undertaken by H.E.S.S., low threshold observations with MAGIC and more recently by operation of VERITAS, have revealed dozens of galactic and extragalactic sources, providing a wealth of information on a variety of high energy acceleration sites in our universe. Also, the water Cherenkov instrument Milagro has provided several extended sources after seven years of data integration. An overview of these results with focus on some of the most recent highlights is given.

#### Gamma-Ray, Neutrino & Gravitational Wave Detection: OG 2.5,2.6,2.7 Rapporteur Rowell, G. (2008)

Abstract: This report is based on a rapporteur talk presented at the 30th International Cosmic Ray Conference held in Merida, Mexico (July 2007), and covers three of the OG sessions devoted to neutrino, gravitational wave, and gamma-ray detection.

#### TeV Gamma-Ray Astrophysics Ribo, M. (2008)

Abstract: The window of TeV Gamma-Ray Astrophysics was opened less than two decades ago, when the Crab Nebula was detected for the first time. After several years of development, the technique used by imaging atmospheric Cherenkov telescopes like HESS, MAGIC or VERITAS, is now allowing to conduct sensitive observations in the TeV regime. Water Cherenkov instruments like Milagro are also providing the first results after years of integration time. Different types of extragalactic and galactic sources have been detected, showing a variety of interesting phenomena that are boosting theory in very high energy gamma-ray astrophysics. Here I review some of the most interesting results obtained up to now, making special emphasis in the field of X-ray/gamma-ray binaries.

#### Gamma-ray Astronomy Hinton, J. (2007)

Abstract: The relevance of gamma-ray astronomy to the search for the origin of the galactic and, to a lesser extent, the ultra-high-energy cosmic rays has long been recognised. The current renaissance in the TeV gamma-ray field has resulted in a wealth of new data on galactic and extragalactic particle accelerators, and almost all the new results in this field were presented at the recent International Cosmic Ray Conference (ICRC). Here I summarise the 175 papers submitted on the topic of gamma-ray astronomy to the 30th ICRC in Merida, Mexico in July 2007.

#### Very-High Energy Gamma Astrophysics De Angelis, A., Mansutti, O. & Persic, M. (2008)

Abstract: High-energy photons are a powerful probe for astrophysics and for fundamental physics under extreme conditions. During the recent years, our knowledge of the most violent phenomena in the Universe has impressively progressed thanks to the advent of new detectors for high-energy gamma-rays. Observation of gamma-rays gives an exciting view of the high-energy universe thanks to satellite-based telescopes (AGILE, GLAST) and to ground-based detectors like the Cherenkov telescopes (H.E.S.S. and MAGIC in particular), which recently discovered more than 60 new very-high-energy sources. The progress achieved with the last generation of Cherenkov telescopes is comparable to the one drawn by EGRET with respect to the previous gamma-ray satellite detectors. This article reviews the present status of high-energy gamma astrophysics, with emphasis on the recent results and on the experimental developments.

#### VHE astrophysics: recent developments Persic, M. & De Angelis, A. (2007)

Abstract: We review the current status, and some open issues, of VHE astrophysics.

#### The Status of VHE Gamma-Ray Astronomy Ong, R. A. (2006)

Abstract: This paper presents a summary of the status of the field of very high-energy (VHE) gamma-ray astronomy, as of early 2006. The paper is based on the Rapporteur Talk given at the 29th International Cosmic Ray Conference in Pune, India (ICRC 2005). It covers astrophysical results from observations made by high-energy and very high-energy telescopes operating at photon energies above 1 GeV. The majority of recent observations in this field have been made by ground-based telescopes using the atmospheric Cherenkov or air shower techniques.

#### TeV Astrophysics, A Review Cui, W. (2006)

Abstract: In this paper I briefly review recent progress in the field of ground-based gamma ray astrophysics.

#### Air Cherenkov methods in cosmic rays: Review and some history Lidvansky, A. S. (2006)

Abstract: The history of application of the Cherenkov light emission in the atmosphere to cosmic ray and gamma-ray astronomy studies is briefly outlined with an emphasis on the pioneering activity of A.E. Chudakov. The present-day situation and some new ideas are also discussed.

#### The Atmospheric Cherenkov Imaging Technique for Very High Energy Gamma-ray Astronomy Weekes, T. C. (2005)

Abstract: The Atmospheric Cherenkov Imaging Technique has opened up the gamma-ray spectrumfrom 100 GeV to 50 TeV to astrophysical exploration. The development of the technique is described as are the basic principles underlying its use. The current generation of arrays of telescopes is briefly described and the early results are summarized.

#### Extragalactic sources of TeV gamma rays: a summary Horan, D. & Weekes, T. C. (2004)

Abstract: The development of techniques whereby gamma rays of energy 100 GeV and above can be studied from the ground, using indirect, but sensitive, techniques has opened up a new area of high energy photon astronomy. The most exciting result that has come from these is the detection of highly variable fluxes of TeV gamma rays from the relativistic jets in nearby AGN. The recent detection of signals from a starburst galaxy and from a radio galaxy opens the possibility that the extragalactic emission of TeV gamma rays is a ubiquitous phenomenon. Here we attempt to summarize the properties of the sources detected so far.

#### The Status of VHE Astronomy Ong, R. A. (2003)

Abstract: This paper summarizes the status of very high-energy (VHE) astronomy, as of early 2003. It concentrates on observations made by gamma-ray telescopes operating at energies above 10 GeV. This field is an exciting one to be working in, with a growing and varied list of established sources that includes plerions, supernova remnants, and active galactic nuclei. New results include the discovery of the first unidentified source at these energies and the detection of gamma rays from a nearby starburst galaxy (NGC 253). The arrival of a new generation of telescopes, both on the ground and in space, argues that we can anticipate a wealth of exciting results in the near future.

#### Multi-messenger astronomy: cosmic rays, gamma-rays and neutrinos Halzen, F. (2002)

Abstract: Although cosmic rays were discovered a century ago, we do not know where or how they are accelerated. There is a realistic hope that the oldest problem in astronomy will be solved soon by ambitious experimentation: air shower arrays of 10,000 kilometer-square area, arrays of air Cerenkov telescopes and kilometer-scale neutrino observatories. Their predecessors are producing science. We will review the highlights: 1) Cosmic rays: the highest energy particles and the GZK cutoff, the search for cosmic accelerators and the Cygnus region, top-down mechanisms: photons versus protons? 2) TeV-energy gamma rays: blazars, how molecular clouds may have revealed proton beams, fist hints of the diffuse infrared background? 3) Neutrinos: first results and proof of concept for technologies to construct kilometer-scale observatories.

#### TeV Gamma-ray Observations and the Origin of Cosmic Rays: I Weekes, T. C. (2003)

Abstract: This is the first of three plenary talks with the same title given at the 28th ICRC in Tsukuba, Japan in August, 2003. A brief description of the techniques for detecting gamma rays at TeV energies is followed by a summary of the observational status of the field. The expectations of the field from a cosmic ray perspective are compared with these early results. The majority of sources detected with some certainty are extragalactic; the observational status of these sources is summarized. The most complete set of observations are those dealing with the detection of blazars for which a catalog is presented. This discipline is now established as a new branch of observational astronomy.

#### Very high energy gamma-ray astronomy Weekes, T. C. (2003)

Book Description: High energy gamma-ray photons are the prime probes of the relativistic or high-energy universe, populated by black holes, neutron stars, supernovae, quasars, and matter-antimatter annihilations. Through studying the gamma-ray sky, astrophysicists are able to better understand the formation and behavior of these exotic and energetic bodies. Very High Energy Gamma-Ray Astronomy summarizes the status of gamma-ray astronomy at energies between 30MeV and 50TeV at a critical point in the development of the discipline: the hiatus between the demise of the EGRET telescope and the launch of the next generation of space telescopes. Starting with an overview of the astrophysics of the bodies that generate high energy gamma rays, it proceeds to discuss the latest developments in observational techniques and equipment. By presenting the techniques, observations, and theories of this expanding frontier, Very High Energy Gamma-Ray Astronomy aids experimentalists and theoreticians in detecting and explaining gamma rays of the highest energies..

#### Gamma-Ray Summary Report Buckley, J. B., et al. (2002)

Abstract: This paper reviews the field of gamma-ray astronomy and describes future experiments and prospects for advances in fundamental physics and high-energy astrophysics through gamma-ray measurements. We concentrate on recent progress in the understanding of active galaxies, and the use of these sources as probes of intergalactic space. We also describe prospects for future experiments in a number of areas of fundamental physics, including: searches for an annihilation line from neutralino dark matter, understanding the energetics of supermassive black holes, using AGNs as cosmological probes of the primordial radiation fields, constraints on quantum gravity, detection of a new spectral component from GRBs, and the prospects for detecting primordial black holes.

#### Status of VHE Astronomy c. 2000 Weekes, T. C. (2001)

Abstract: The status of VHE Astronomy is reviewed.

#### GeV-TeV Gamma-ray Astronomy Mori, M. (2001)

Abstract: Recent results of GeV and TeV observations of gamma-rays from the Universe are briefly reviewed. Topics include observational technique, diffuse gamma-rays, pulsars, unidentified sources, plerions, supernova remnants and AGNs.

#### Gamma Ray Astronomy Pohl, M. (2001)

Abstract: This paper summarizes recents results in gamma-ray astronomy, most of which were derived with data from groundbased gamma-ray detectors. Many of the contributions presented at this conference involve multiwavelength studies which combine ground-based gamma-ray measurements with optical data or space-based X-ray and gamma-ray measurements. Besides measurements of the diffuse emission from the Galaxy, observations of blazars, gamma-ray bursts, and supernova remnants this paper also covers theoretical models for the acceleration of radiating particles and their emission mechanisms in these sources.

#### Gamma ray astronomy Buckley, J. H. (2000)

Abstract: This paper summarizes recent results in X-ray and gamma-ray stronomy including measurements of galactic and extragalactic sources from 0.1 keV to 20 GeV from space, measurements of gamma-rays at energies above 70 GeV from the ground as well as theoretical models for the emission of gamma-rays and X-rays in galactic and extragalactic sources. The majority of the new results presented at this conference were made with ground-based gamma-ray detectors, with relatively few new results from the Compton Gamma-ray Observatory (CGRO) and other space-based instruments. Many of the results involve multiwavelength studies which combine ground-based gamma-ray measurements with space based X-ray and gamma-ray measurements. The main topics covered in this paper include observations of diffuse gamma-ray emission from the galaxy, observations of blazars, gamma-ray bursts, supernova remnants and pulsars as well as theoretical models for the emission mechanisms of these sources.

#### Particle Astrophysics with High Energy Photons Weekes, T. C. (2000)

Abstract: Not Available.

#### VHE Astronomy Before the New Millennium Weekes, T. C. (2000)

Abstract: A report on the observational status of VHE astronomy is given.

#### High Energy Gamma Rays Mukherjee, R. (2000)

Abstract: This article reviews the present status of high energy gamma-ray astronomy at energies above 30 MeV. Observations in the past decade using both space- and ground-based experiments have been primarily responsible for giving a tremendous boost to our knowledge of the high energy Universe. High energy gamma-rays have been detected from a wide range of Galactic and extragalactic astrophysical sources, such as gamma-ray bursters, pulsars, and active galaxies. These observations have established high energy gamma-ray astronomy as a vital and exciting field, that has a bright future. This review summarizes the experimental techniques, observations and results obtained with recent experiments, and concludes with a short description of future prospects.

#### Gamma-ray astronomy at high energies Hoffman, C. M., Sinnis, C., Fleury, P. & Punch, M. (1999)

Abstract: Progress in high-energy gamma-ray astronomy has depended upon the development of sophisticated detectors and analysis techniques. Observations in this decade using space-based and ground-based detectors have observed gamma-ray emission from a variety of sources. For the first time a consistent picture of the gamma-ray sky has emerged. This article describes the detection techniques in gamma-ray astronomy, the nature of the astrophysical objects studied, and the present state of the observations. Several possible new directions in the field are also described.

#### Very High Energy Gamma-Ray Astronomy Catanese, M. & Weekes, T. C. (1999)

Abstract: We present a review of the current status of very high energy gamma-ray stronomy has led to a rapid growth in the number of observatories. The detection of TeV gamma-rays from active galactic nuclei was unexpected and is providing new insights into the emission mechanisms in the jets. Next-generation telescopes are under construction and will increase dramatically the knowledge available at this extreme end of the cosmic electromagnetic spectrum.

#### A General Gamma-Ray Source Catalog Macomb, D. J. & Gehrels, N. (1999)

Abstract: The past several years have seen unprecedented growth in the field of gamma-ray astronomy. Highly successful missions such as the Compton Gamma-Ray Observatory (CGRO) have led to both a great increase in the number of detected gamma-ray sources and a more fundamental understanding of the basic physical processes involved for those sources. New ground-based observatories, the Rossi X-Ray Timing Explorer (RXTE), and the SIGMA instrument aboard the GRANAT spacecraft have all contributed to this explosion. Detailed observations of active galaxies, pulsars, accreting binaries, and diffuse emission have had a tremendous impact on our view of the universe. Given that new experiments that will provide a similar increase in source numbers are several years away, it is a good time to take inventory of the state of gamma-ray astronomy. To this end, we have developed a general gamma-ray point-source catalog containing 309 objects that summarize the field. Gamma-ray astronomy, as we define it, includes photon energies from 50 keV to about 1 TeV. While many catalogs concentrate on a single type of astronomical object and/or a very restricted energy range, the nature of this catalog is somewhat different. The large variety of objects and the many orders of magnitude in energy space covered by gamma-ray astronomy presents an organizational challenge. We focus on two main types of information: a general listing of the basic characteristics of each source, and detailed tables of a representative sample of high-energy observations. We also summarize the gamma-ray instruments whose observations are included in the catalog.

#### Very high-energy gamma-ray astronomy Ong, R. A.

Abstract: Very high-energy gamma-ray astronomy has emerged as an exciting and vital field. In the last seven years, major discoveries have been made by experiments in space and on the ground. In space, instruments on the Compton Gamma Ray Observatory have identified high-energy emission from a variety of astrophysical sources, including gamma-ray bursts, spin-down pulsars, and active galaxies of the blazar type. Remarkably, a number of these sources have now been detected at much higher energies by ground-based instruments. This review will concentrate on the methodology and results from these ground-based experiments, currently operating at energies above 250 GeV. The ground-based detections are for the first time statistically compelling and stand in direct contrast to earlier results reported in the 1980s. The future scientific and experimental prospects for the field appear excellent and are summarized.

#### Very high-energy gamma-ray astronomy Ong, R. A. (1998)

Abstract: Very high-energy gamma-ray astronomy has emerged as an exciting and vital field. In the last seven years, major discoveries have been made by experiments in space and on the ground. In space, instruments on the Compton Gamma Ray Observatory have identified high-energy emission from a variety of astrophysical sources, including gamma-ray bursts, spin-down pulsars, and active galaxies of the blazar type. Remarkably, a number of these sources have now been detected at much higher energies by ground-based instruments. This review will concentrate on the methodology and results from these ground-based experiments, currently operating at energies above 250 GeV. The ground-based detections are for the first time statistically compelling and stand in direct contrast to earlier results reported in the 1980s. The future scientific and experimental prospects for the field appear excellent and are summarized..

#### TeV Gamma-ray Astronomy: New Light from the Dark Sky Weekes, T. C. (1997)

Abstract: High energy astrophysics, in particular high energy gamma-ray astronomy, has generally been considered as in the domain of space astronomy. Somewhat surprisingly, very high energy gamma ray astronomy can be pursued using ground-based techniques. The air showers generated by the interaction of gamma rays in the atmosphere can be detected using rather simple optical detectors to register the Cherenkov radiation in the atmosphere. In recent years the atmospheric Cherenkov imaging technique, which has been mostly developed at the Whipple Observatory, has been shown to be extremely sensitive to gamma-ray fluxes in the 200 GeV to 10 TeV energy region. The major breakthrough came with the detection of the Crab Nebula which has now been established as the standard candle for the new discipline. Although other supernova remnants have been detected, it appears that in all cases the gamma rays come from Compton scattering by electrons in the synchrotron nebula surrounding the pulsar. TeV gamma-ray astronomy has not yet provided the "smoking gun" for shock acceleration of hadrons in supernova remnants, the canonical picture of cosmic ray production in the Galaxy. BL Lac objects are also powerful sources of TeV gamma rays; in this case the observed gamma rays are almost certainly associated with the relativistic particles in the jets. Doubling times as short as 15 minutes have been observed in Markarian 421. In 1997 Markarian 501 has been in a state of high emission making it the brightest TeV source in the sky. A new generation of telescopes (e.g. VERITAS) is now at an advanced state of planning and will complement the next generation of high energy gamma-ray space telescopes (e.g. GLAST).

#### The Atmospheric Cherenkov Technique in Very High Energy Gamma-Ray Astronomy Weekes, T. C. (1996)

Abstract: Not available.

#### TeV Gamma-Ray Astronomy in South Africa Raubenheimer, B. C. (1995)

Abstract: Not Available.

#### Gamma Ray Astronomy at TeV Energies Weekes, T. C. (1994)

Abstract: Cosmic sources of gamma-rays of energy in excess of 0.25 TeV are now well-established using the ground-based atmospheric Cherenkov technique. Recently high resolution cameras (arrays of phototubes) on large optical reflectors have achieved significant improvements in flux sensitivity. Observations with the Compton Gamma Ray Observatory have shown that many sources have significant fluxes at the highest useful energy of EGRET (30 GeV); at least three of these sources have been detected in the TeV energy range. The Crab Nebula is the best established source; its spectrum extends beyond 10 TeV and is well understood in terms of a Compton-synchrotron model. PSR1706-044 is one of five pulsars seen by EGRET but at TeV energies it is seen as a steady (unpulsed) source. Markarian 421 is closest AGN seen by EGRET; at TeV energies it is a strong and variable source. The failure to detect emission from other stronger, but more distant, AGN's has led to speculation that the intergalactic infrared background is responsible for significant absorption causing photon-photon pair production. It is thus possible to derive an upper limit to the intergalactic infrared background. New telescopes are under development which will reduce the energy threshold of the atmospheric Cherenkov technique and bridge the gap to space gamma-ray telescopes. Supported in part by the U.S. Dept. of Energy.

#### The search for discrete astrophysical sources of energetic gamma radiation Cronin, J. W., Gibbs, K. & Weekes, T. C. (1993)

Abstract: Not Available

#### TeV radiation from galactic sources Weekes, T. C. (1992)

Abstract: The detection of the Crab Nebula as a steady source of TeV gamma rays puts the field of Very High Energy Gamma-Ray Astronomy on a firm observational basis and permits a critical reassessment of the claims for the detection of a multitude of episodic binary sources. A new generation of detectors in the TeV and PeV energy regions is coming on-line; together with the telescopes of the Gamma-Ray Observatory, these instruments will present a new perspective on one of the last frontiers of astronomy.

#### TOPICAL REVIEW: Very high energy gamma rays from x-ray binary pulsars Chadwick, P. M., McComb, T. J. & Turver, K. E. (1990)

Abstract: Not Available

#### Very high energy gamma-ray astronomy Weekes, T. C. (1988)

Abstract: Not Available

#### Cerenkov Radiation from the Night Sky, and its Application to Gamma-Ray Astronomy Jelley, J. V. & Porter, N. A. (1963)

Abstract: Not Available.

 Note: If the Abstract section reads "Not Available", this means that the abstract was not posted on ADS. If the abstract of a paper is submitted to us, we will post it here.