TeV GAMMA RAYS: OBSERVATIONS VERSUS EXPECTATIONS & THEORY

The scope of this paper is to discuss two important questions relevant for TeV γ-ray astronomy; the pursuit to reveal the origin of cosmic rays in our galaxy, and the opacity of the universe in γ-rays. The origin of cosmic rays stipulated the field of TeV astronomy in the first place, and led to the development of the atmospheric Cherenkov technique; significant progress has been made in the last decade through the detection of several supernova remnants, the primary suspects for harboring the acceleration sites of cosmic rays. TeV γ-rays propagate mostly unhindered through the galactic plane, making them excellent probes of processes in SNRs and other galactic sources. Key results related to the SNR origin of cosmic rays are discussed. TeV γ-ray spectra from extragalactic sources experience significant absorption when traversing cosmological distances. The opacity of the universe to γ-rays above 10 GeV progressively increases with energy and redshift; the reason lies in their pair production with ambient soft photons from the extragalactic background light (EBL). While this limits the γ-ray horizon, it offers the opportunity to gain information about cosmology, i.e. the EBL intensity, physical conditions in intergalactic space, and potentially new interaction processes. Results and implications pertaining to the EBL are given

A Fast Topological Trigger for Real Time Analysis of Nanosecond Phenomena; Opening the Gamma Ray Window to Our Universe

This work was to enable the development of a proof-of-principle nanosecond trigger system that is designed to perform a real time analysis of fast Cherenkov light flashes from air showers. The basic building blocks of the trigger system have been designed and constructed, and a real world system is now operating in the VERITAS experiment

New Generation Atmospheric Cherenkov Detectors

High energy gamma-ray astronomy has been established during the last decade through the launch of the Compton Gamma Ray Observatory (CGRO) and the success of its ground-based counterpart, the imaging atmospheric Cherenkov technique. In the aftermath of their important and surprising scientific results a worldwide effort developing and designing new generation atmospheric Cherenkov detectors is underway. These novel instruments will have higher sensitivity at E > 250 GeV, but most importantly, will be able to close the unexplored energy gap between 20 GeV and 250 GeV. Several ground-based detectors are proposed or under construction. Aspects of the techniques used and sensitivity are discussed in this overview paper. The instruments cover largely complementary energy ranges and together are expected to explore the gamma-ray sky between 20 GeV and 100 TeV with unprecedented sensitivity.Comment: 13 pages, 4 Figures, Invited talk at the VERITAS Workshop on TeV Astrophysics of Extragalactic Sources, eds. M. Catanese and T. Weekes, to be published in Astroparticle Physic