O. Tumay Tumer

A promising large area VHE gamma ray detector with excellent hadron rejection capability

Abstract A new large area VHE gamma ray detector for detecting atmospheric Cerenkov light from very high energy celestial gamma rays is proposed. It will be constructed by converting Solar One, a 10 MW Solar Thermal Central Receiver Pilot Plant at Barstow, California, which uses the solar tower technology with heliostats as light collectors. Solar energy research at this facility has recently been terminated. The detector will cover an area of at least 200 m diameter, which is only about 5% of the total area available at Solar One, so that a significant fraction of the Cerenkov light pool is detected. Each heliostat will focus the Cerenkov light onto a photomultiplier tube (PMT) selected to match the optical quality of the heliostat. Its active reflecting surface is 71,000 m2, which is about 375 times larger than the largest VHE gamma ray atmospheric Cerenkov detector, the twin 11 m dia. collectors at Sandia Labs, Albuquerque1. It is expected to have the lowest energy threshold (≥10 GeV) for atmospheric Cerenkov observations. This will enhance counting rates significantly and bridge the gap between HE and VHE gamma ray astronomy with some overlapping. It will also have excellent inherent hadron rejection. One hundred million dollars worth of installation is already constructed and ready to use. The rest of the detector can be built for a small fraction,

A search for gamma rays of 1. 5-20. 0 MeV from Centaurus A

A search for a gamma-ray continuum and lines from Centaurus A is reported. No measurable gamma rays are found in the 1.5-20.0 MeV and 3 sigma upper limits are reported for various energies which are about a factor of two lower than the results reported by von Ballmoos et al. (1987). These upper limits, along with those of SAS 2 and COS B, suggest that the energy distribution turns over in the energy range of 500 keV to a few MeV. A high source temperature of 5 MeV or synchrotron self-Compton models for producing an excess of gamma rays of a few MeV do not appear necessary. 16 refs.

Comptel science module III neutron calibration and simulation

Calibration results of COMPTEL’s Science Model III (SM3) for neutrons at energies of 18.5, 35.7, 77.0, and 132.1 MeV are compared with simulation. The SM3 calibration was used to obtian the full COMPTEL neutron response and was carried out at the Indiana Cyclotron Facility. The Monte Carlo results of the SM3 neutron simulation were obtained using the combined MCNPv4.2 (Monte Carlo Neutron Photon) and LAHET (Los Alamos High Energy Transport) codes developed at Los Alamos. The calibration and simulation efficiencies for SM3 were 0.031, 0.014, 0.010, and 0.0083 percent and 0.013, 0.0075, 0.0043 and 0.0018 percent at 18.5, 35.7, 77.0 and 132.1 MeV, respectively. The simulated SM3 analysis compare well with the SM3 calibration and provide confidence for the efficiencies obtained for the full COMPTEL instrument simulation.