Gamma-ray astronomy

Abstract:

Over the last 25 years ∼75% of the low-mass X-ray binary X-ray transients have been shown to contain black-hole compact objects, based on optical spectroscopy of their kinematics when in quiescence. Because many of these systems are extremely faint in quiescence and unobservable, we have utilised the method of studying them when in X-ray outburst that exploits the fluores- cence features produced by X-ray irradiation of the donor's inner face, thereby allowing us to track the motion of the donor. Such outbursts are unpredictable and hence these studies must necessarily be through Target-of-Opportunity programs, and hence are ideal for SALT for accessible targets. Here we report on our SALT ToO studies of two transients, both believed to contain black holes and both at high galactic latitude.

Abstract:

The small size telescopes (SSTs), spread over an area of several square km, dominate the CTA sensitivity in the photon energy range from a few TeV to over 100 TeV, enabling for the detailed exploration of the very high energy gamma-ray sky. The proposed telescopes are innovative designs providing a wide field of view. Two of them, the ASTRI (Astrophysics con Specchi a Tecnologia Replicante Italiana) and the GCT (Gamma-ray Cherenkov Telescope) telescopes, are based on dual mirror Schwarzschild-Couder optics, with primary mirror diameters of 4 m. The third, SST-1M, is a Davies-Cotton design with a 4 m diameter mirror. Progress with the construction and testing of prototypes of these telescopes is presented. The SST cameras use silicon photomultipliers, with preamplifier and readout/trigger electronics designed to optimize the performance of these sensors for (atmospheric) Cherenkov light. The status of the camera developments is discussed. The SST sub-array will consist of about 70 telescopes at the CTA southern site. Current plans for the implementation of the array are presented.

Abstract:

Energy-dependent patterns in the arrival directions of cosmic rays are searched for using data of the Pierre Auger Observatory. We investigate local regions around the highest-energy cosmic rays with [Formula: see text] eV by analyzing cosmic rays with energies above [Formula: see text] eV arriving within an angular separation of approximately 15[Formula: see text]. We characterize the energy distributions inside these regions by two independent methods, one searching for angular dependence of energy-energy correlations and one searching for collimation of energy along the local system of principal axes of the energy distribution. No significant patterns are found with this analysis. The comparison of these measurements with astrophysical scenarios can therefore be used to obtain constraints on related model parameters such as strength of cosmic-ray deflection and density of point sources.