An Analog Trigger System for Atmospheric Cherenkov Telescopes

Arrays of Cherenkov telescopes typically use multi-level trigger schemes to keep the rate of random triggers from the night sky background low. At a first stage, individual telescopes produce a trigger signal from the pixel information in the telescope camera. The final event trigger is then formed by combining trigger signals from several telescopes. In this poster, we present a possible scheme for the Cherenkov Telescope Array telescope trigger, which is based on the analog pulse information of the pixels in a telescope camera. Advanc

The MAGIC highlights of the gamma ray binary LS I +61 303

The discovery of emission of TeV gamma rays from X-ray binaries has triggered an intense effort to better understand the particle acceleration, absorption, and emission mechanisms in compact binary systems. Here we present the pioneering effort of the MAGIC collaboration to understand the very high energy emission of the prototype system LS I +61 303. We report on the variable nature of the emission from LS I +61 303 and show that this emission is indeed periodic. The system shows regular outburst at TeV energies in phase phi=0.6-0.7 and detect no signal at periastron (phi~ 0.275). Furthermore we find no indication of spectral variation along the orbit of the compact object and the spectral energy distribution is compatible with a simple power law with index Gamma=2.6+-0.2_(stat)+-0.2_(sys). To answer some of the open questions concerning the emission process of the TeV radiation we conducted a multiwavelength campaign with the MAGIC telescope, XMM-Newton, and Swift in September 2007. We detect a simultaneous outburst at X-ray and TeV energies, with the peak at phase 0.62 and a similar shape at both wavelengths. A linear fit to the strictly simultaneous X-ray/TeV flux pairs provides r=0.81 -0.21 +0.06. Here we present the observations and discuss the implications of the obtained results to the emission processes in the system.

The propagation of ultra-high energy tau leptons and neutrinos while skimming the Earth

The detection of Earth-skimming tau neutrinos has turned into a very promising strategy for the observation of UHE cosmic neutrinos. The sensitivity of this channel crucially depends on the parameters of the propagation of the tau neutrino (and the tau lepton) through the terrestrial crust, which governs the flux of emerging tau leptons that can be detected. This propagation problem is usually treated in a simplified framework where several effects are neglected, e.g. the possibility of multiple regenerations of the tau neutrino, the weak interactions of the tau lepton, as well as the stochastic nature of its energy losses. We discuss here the validity of such approximations by studying the propagation in standard rock of tau leptons and neutrinos with both mono-energetic and power-law spectra. We also investigate the impact of such simplifications in non-standard scenarios for the neutrino-nucleon interactions as well as for the tau energy losses.

Limits to the diffuse flux of UHE tau neutrinos at EeV energies from the Pierre Auger Observatory

With the Pierre Auger Observatory we have the capability of detecting ultra-high energy neutrinos by searching for very inclined showers with a significant electromagnetic component. In this work we discuss the discrimination power of the instrument for earth skimming tau neutrinos with ultra-high energies. Based on the data collected since January 2004 an upper limit to the diffuse flux of neutrinos atEeV energies is presented and systematic uncertainties are discussed.