OSETI with STACEE: A Search for Nanosecond Optical Transients from Nearby Stars

We have used the STACEE high-energy gamma-ray detector to look for fast blue-green laser pulses from the vicinity of 187 stars. The STACEE detector offers unprecedented light-collecting capability for the detection of nanosecond pulses from such lasers. We estimate STACEE's sensitivity to be approximately 10 photons per square meter at a wavelength of 420 nm. The stars have been chosen because their characteristics are such that they may harbor habitable planets and they are relatively close to Earth. Each star was observed for 10 minutes and we found no evidence for laser pulses in any of the data sets.Comment: 38 pages, 12 figures. Accepted for publication in Astrobiolog

Very high-energy observations of the two high-frequency peaked BL Lac objects 1ES 1218+304 and H 1426+428

We present results of very-high-energy gamma-ray observations (E > 160 GeV) of two high-frequency-peaked BL Lac (HBL) objects, 1ES 1218+304 and H 1426+428, with the Solar Tower Atmospheric Cherenkov Effect Experiment (STACEE). Both sources are very-high-energy gamma-ray emitters above 100 GeV, detected using ground-based Cherenkov telescopes. STACEE observations of 1ES 1218+304 and H 1426+428 did not produce detections; we present 99% CL flux upper limits for both sources, assuming spectral indices measured mostly at higher energies

New Limits to the Infrared Background: Bounds on Radiative Neutrino Decay and on Contributions of Very Massive Objects to the Dark Matter Problem

From considering the effect of γ-γ interactions on recently observed TeV gamma-ray spectra, improved limits are set to the density of extragalactic infrared photons which are robust and essentially model independent. The resulting limits are more than an order of magnitude more restrictive than direct observations in the 0.025–0.3 eV regime. These limits are used to improve constraints on radiative neutrino decay in the mass range above 0.05 eV and to rule out very massive objects as providing the dark matter needed to explain galaxy rotation curves. Lower bounds on the maximum distance which TeV gamma rays may probe are also derived