arXiv subjects
Publications and source records attributed to E. Colombo.
Studies of the composition of the highest energy cosmic rays with the Pierre Auger Observatory, including examination of hadronic physics effects on the structure of extensive air showers. Submissions to the 31st ICRC, Lodz, Poland (July 2009).
AMIGA (Auger Muons and Infill for the Ground Array) constitutes an enhancement for the Pierre Auger Observatory. It consists of a denser array of surface detectors and muon counters whose objective is both to extend the detection range down to 10^17 eV and to help towards mass composition determination. The latter is to be achieved with muon counters since the shower muon content is one of the best parameter for particle type identification. In this work, we present the study of a muon counter prototype. The prototype was buried 3 m deep in an effort to avoid signal contamination from the shower electromagnetic component. We study the performance of the detector before and after burying it with its associated electronic components. The detector validation is performed from signal analysis of charged particles traversing the counter.
From direct observations of the longitudinal development of ultra-high energy air showers performed with the Pierre Auger Observatory, upper limits of 3.8%, 2.4%, 3.5% and 11.7% (at 95% c.l.) are obtained on the fraction of cosmic-ray photons above 2, 3, 5 and 10 EeV (1 EeV = 10^18 eV) respectively. These are the first experimental limits on ultra-high energy photons at energies below 10 EeV. The results complement previous constraints on top-down models from array data and they reduce systematic uncertainties in the interpretation of shower data in terms of primary flux, nuclear composition and proton-air cross-section.
We have searched for possible sites in Argentina for the installation of large air Cherenkov telescope arrays and water Cherenkov systems. At present seven candidates are identified at altitudes from 2500 to 4500 m. The highest sites are located at the Northwest of the country, in La Puna. Sites at 2500 and 3100 m are located in the West at El Leoncito Observatory, with excellent infrastructure. A description of these candidate sites is presented with emphasis on infrastructure and climatology.
PSR B1951+32 is a gamma-ray pulsar detected by the Energetic Gamma Ray Experiment Telescope (EGRET) and identified with the 39.5 ms radio pulsar in the supernova remnant CTB 80. The EGRET data shows no evidence for a spectral turnover. Here we report on the first observations of PSR B1951+32 beyond 30 GeV. The observations were carried out with the 10m gamma-ray telescope at the Whipple Observatory on Mt. Hopkins, Arizona. In 8.1 hours of observation we find no evidence for steady or periodic emission from PSR B1951+32 above ~260 GeV. FLux upper limits are derived and compared with model extrapolations from lower energies and the predictions of emission models.