Book Review: "Cherenkov Reflections: Gamma-Ray Imaging and the Evolution of TeV Astronomy by David Fegan"

Abstract

Journal of Astronomical InstrumentationVol. 08, No. 04, 1980003 (2019) Book ReviewFree AccessBook Review: "Cherenkov Reflections: Gamma-Ray Imaging and the Evolution of TeV Astronomy by David Fegan"Stefan WagnerStefan WagnerHeidelberg-Königstuhl State Observatory, Center for Astronomy, Heidelberg University, Germanyhttps://doi.org/10.1142/S2251171719800035Cited by:0 PreviousNext AboutSectionsPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack CitationsRecommend to Librarian ShareShare onFacebookTwitterLinked InRedditEmail (World Scientific, 2019)Astronomical research is conducted in an amazingly broad part of the electromagnetic spectrum. The exploration of the universe at the very high energy end is a relatively recent chapter in this story — as far as actual discoveries and physics interpretation is concerned. The experimental techniques have been in development for more than two generations, however, and the early days have not been recorded in a comprehensive fashion as often and as detailed as in other branches of astronomy. David Fegan’s reflections on the history of Cherenkov astronomy provide a detailed and comprehensive insider’s account on the meandering path that led to the recognition that this field enjoys today.Cherenkov astronomy is different from other branches in many ways. The primary gamma-photons are reconstructed after having launched an avalanche of relativistic particles, which, in turn, generate a nano-second-lasting flash of Cherenkov light. The atmosphere — generally a troublesome, annoying or forbidding screen in observational astronomy — provides the detector volume, the light recorded by the cameras is emitted several kilometers above the telescopes rather than from kiloparsec or gigaparsec distances, and the original photons have to be reconstructed one by one.With photon energies 10 to 18 orders of magnitude higher than in the radio to X-ray regime, photon rates are typically more than 20 to 36 orders of magnitude lower, and there is the overwhelming isotropic background of cosmic rays that also initiate showers and Cherenkov flashes that are difficult to discriminate against. These obstacles provided many challenges to the pioneers and many generations of PhD students and it is amazing to follow their persistence.David Fegan takes the reader on a tour that covers this difficult period between the early ideas and the breakthrough that was triggered by the first indisputable discoveries. Following a brief introduction on the motivations provided by the discovery of cosmic rays and a concise chapter of the early work in the 1950s, 12 of the 15 chapters describe the progress from the early 1960s, when the author started his active involvement, to the early 1990s when the first real source discoveries started the path that took the field to mainstream astrophysics.The text has a rich store of personal recollections and insider information that can hardly be distilled from published work. The main focus lies on detailed descriptions of the different experimental set-ups, cameras, telescopes and experimental methods developed by many small and widely distributed groups. The text reiterates the motivation and enables the reader to understand why many paths have been taken that ultimately proved to be dead ends. While it is difficult in several cases to see why certain choices were made, the reader cannot fail to appreciate the persistence of the small community to overcome obstacles and disappointments. The need for rigor in eliminating plausible but ultimately false detections and the necessity of open-mindedness are made very obvious throughout the book.The detailed story ends with the first discoveries made with the Whipple telescope around 1990 and reflections on whether the path could have been straighter. The subsequent decade of building the current generation of observatories, the many discoveries, and the development of VHE gamma-ray astrophysics are only sketched in a final chapter that takes the reader to the current planning of the future Cherenkov Telescope Array (CTA). The book is not about the history of Cherenkov astronomy but a book on the evolution of experimental concepts in a branch of what is now known as particle astrophysics. It will be an interesting read for any interested in the history of science in general and high-energy astrophysics (or particle astrophysics) in particular. The admirable persistence of the founding fathers of TeV astronomy in what appears to have been a more daring endeavor in retrospect is well captured. FiguresReferencesRelatedDetails Recommended Vol. 08, No. 04 Metrics History Received 5 November 2019 Published: 13 November 2019 PDF download