S. D. Biller

Limits to Quantum Gravity Effects on Energy Dependence of the Speed of Light from Observations of TeV Flares in Active Galaxies

We have used data from the TeV γ-ray flare associated with the active galaxy Markarian 421 observed on 15 May 1996 to place bounds on the possible energy-dependence of the speed of light in the context of an effective quantum gravitational energy scale. The possibility of an observable time dispersion in high energy radiation has recently received attention in the literature, with some suggestions that the relevant energy scale could be less than the Planck mass and perhaps as low as 10GeV. The limits derived here indicate this energy scale to be in excess of 4 × 10GeV at the 95% confidence level. To the best of our knowledge, this constitutes the first convincing limit on such phenomena in this energy regime. Submitted to Physical Review Letters

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.

The spectrum of TeV gamma rays from the Crab Nebula

The Crab Nebula has become established as the standard candle for TeV gamma-ray astronomy. No evidence for variability has been seen. The spectrum of gamma rays from the Crab Nebula has been measured in the energy range 500 GeV to 8 TeV at the Whipple Observatory. Two methods of analysis involving independent Monte Carlo simulations and two databases of observations (1988–89 and 1995–96) were used and give close agreement. Using the complete spectrum of the Crab Nebula, the spectrum of relativistic electrons is deduced and the spectrum of the resulting inverse Compton gamma-ray emission is in good agreement with the measured spectrum if the ambient magnetic field is ∼25–30 nT.

Probing Majorana neutrinos in the regime of the normal mass hierarchy

An approach to developing a feasible neutrinoless double beta decay experiment capable of probing Majorana masses in the regime of the nondegenerate normal neutrino mass hierarchy is proposed. For such an experiment, this study suggests that 130Te is likely the best choice of candidate isotope and that metal-loaded liquid scintillator likely represents the best choice of detector technology. An evaluation of the required loading, scintillator properties and detector configuration is presented. While further development of Te-loaded liquid scintillator is required, recent progress in this area suggests that this task may not be insurmountable. This could open the door for a future experiment of unparalleled sensitivity that might be accommodated in a volume of the order of 10-20 kilotons. To the best of our knowledge, this is the first time that a potentially practical experimental approach to exploring Majorana neutrino masses in the nondegenerate normal hierarchy has been suggested.

A SEARCH FOR CORRELATIONS OF TeV GAMMA RAYS WITH ULTRA-HIGH-ENERGY COSMIC RAYS

A search was conducted for TeV γ-rays emitted from the direction of the ultra-high-energy cosmic ray detected by the Flys Eye experiment with energy E ~ 3 × 1020 eV. No enhancement was found at a level of 10-10γ cm-2 s-1 for E > 350 GeV. A steady source of ultra-high-energy cosmic ray protons or photons would be expected to produce a γ-ray flux above this level. An upper limit was also set for the flux of TeV γ-rays from 3C 147, the most prominent active galactic nucleus in the error box.

Science capabilities of the VERITAS array of 10 m imaging atmospheric Cherenkov gamma-ray detectors

The Very Energetic Radiation Imaging Telescope Array System (VERITAS) is an array of seven 10m aperture telescopes used for gamma-ray astronomy in the 50 GeV to 50 TeV (1 TeV= 1012 electron Volt) energy range. The gamma rays are detected by measuring the optical Cherenkov light emitted by the cascade of electromagnetic particles that is generated by interactions of the high energy gamma-ray with the Earths Atmosphere. This paper describes the science goals of the VERITAS array, a description of the array, and expected performance of the instrument.