Vely high energy (we) y-ray astronomy using the ground based atmospheric Cerenkov technique is an imporiant new field of high energy astrophysics, and a range of W E y r a y sources has been detected at various levels of signifxance by a number of experimental groups. Outstanding widence far -prays from the Crab Nebula was obtained by the Whipple collaboration. This involved the use of a sophisticated technique based on computer simulations to select 7-ray-Iike events from the proton induced background.When this same technique was applied to data from other sources detected using an eariier version oi ihe ' $"nippie ieiescope, ihe evidence ior a yray signai disappeared. D e inability to reconcile Ihe Whipple result from the Crab Nebula with both the failure of the Whipple camera to detect other objects and the detections made with other non-imaging telexopg has caused some concern at a critical time in the evolution of this branch of high energy astrophysics. In an attempt to reconcile t h m results, we have made a detailed study of the effects of the geomagnetic field on the electron-photon cascades. We have simulated the i'erenkov light produced by individual prolans and y-rays at different orientations in the atmosphere, and made measurements of the sensitivily of our obsewations to the geomagnetic field. Indications are that these geomagnetic effects may be a cause of the differing results.

A recent analysis of the Fermi Large Area Telescope data provided evidence for a high-intensity emission of high-energy gamma rays with a E −2 spectrum from two large areas, spanning 50 • above and below the Galactic centre (the "Fermi bubbles"). A hadronic mechanism was proposed for this gamma-ray emission making the Fermi bubbles promising source candidates of high-energy neutrino emission. In this work Monte Carlo simulations regarding the detectability of high-energy neutrinos from the Fermi bubbles 4 with the future multi-km 3 neutrino telescope KM3NeT in the Mediterranean Sea are presented. Under the hypothesis that the gamma-ray emission is completely due to hadronic processes, the results indicate that neutrinos from the bubbles could be discovered in about one year of operation, for a neutrino spectrum with a cutoff at 100 TeV and a detector with about 6 km 3 of instrumented volume. The effect of a possible lower cutoff is also considered.

Experiments are in progress to prepare for intensity interferometry with arrays of air Cherenkov telescopes. At the Bonneville Seabase site, near Salt Lake City, a testbed observatory has been set up with two 3-m air Cherenkov telescopes on a 23-m baseline. Cameras are being constructed, with control electronics for either off-or online analysis of the data. At the Lund Observatory (Sweden), in Technion (Israel) and at the University of Utah (USA), laboratory intensity interferometers simulating stellar observations have been set up and experiments are in progress, using various analog and digital correlators, reaching 1.4 ns time resolution, to analyze signals from pairs of laboratory telescopes.

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A light injection system using LEDs and optical fibres was designed for the calibration and monitoring of the photomultiplier array of the SNO+ experiment at SNOLAB. Large volume, non-segmented, low-background detectors for rare event physics, such as the multi-purpose SNO+ experiment, need a calibration system that allow an accurate and regular measurement of the performance parameters of their photomultiplier arrays, while minimising the risk of radioactivity ingress. The design implemented for SNO+ uses a set of optical fibres to inject light pulses from external LEDs into the detector. The design, fabrication and installation of this light injection system, as well as the first commissioning tests, are described in this paper. Monte Carlo simulations were compared with the commissioning test results, confirming that the system meets the performance requirements. yield and attenuation length -, a high flashpoint and its chemical compatibility with acrylic. With the new target material, several changes to the detector were needed, including new scintillator processing and purification systems, new trigger and readout electronics and new calibration systems. Structural improvements were required since the relative density of LAB is 0.86, causing a significant buoyant force on the scintillator-filled AV. This force is countered by means of a rope net [4] that is anchored to the floor of the detector cavity.The use of liquid scintillator opens up the range of physics goals, making SNO+ a multipurpose experiment. The main goal of SNO+ is the search for neutrinoless double-beta decay (0νβ β ), by loading a large mass of a suitable isotope into the liquid scintillator. When compared to experiments based on solid state detectors, the strategy of SNO+ is to compensate the lower energy resolution with a large mass of isotope and low background. The chosen isotope for SNO+ is 130 Te, with high natural abundance and favourable (0νβ β ) nuclear matrix elements and phase space, and a relatively small two-neutrino double seta decay rate. The optical absorption of Te in the loaded scintillator impacts the detector performance, limiting the initial concentration to 0.3%. Without the Tellurium loading, several solar neutrino measurements can be carried out at SNO+, including a precision measurement of the pep neutrino flux, observation of the low energy survival probability rise in 8 B neutrinos and, possibly, direct measurements of the CNO neutrinos and the pp neutrinos. The observation of anti-neutrinos from nuclear reactors in Ontario and from the natural radioactivity chains of Uranium and Thorium present in the Earth's crust and mantle are additional goals. Throughout all the data-taking phases, the detector will also be part of the SNEWS [5] network monitoring for supernova neutrinos.The physics goals of SNO+ require a low energy threshold, for measurements of solar neutrino elastic scattering signals, and for the tagging of decays of radioactive isotopes needed for the reduction of backgrounds in the 130 Te 0νβ β region-...