Contribution to the 30th International Cosmic Ray Conference, Merida, Mexico, July 2007

  As part of the normal operation of the Whipple 10m Gamma Ray telescope, ten minute drift scan " zenith" runs are made each night of observation for use as calibration. Most of the events reco rded during a zenith run are due to the background of cosmic ray showers. However, it would be possible for a hitherto unknown source of gamma rays to drift through the field. This paper rep orts the results of a search for serendipitous high energy gamma ray sources in the Whipple 10m nightly calibration zenith data. From 2000-2004 nightly calibration runs were taken at an elevation of 89 degrees. A 2-D analysis of these drift scan runs produces a strip of width ~ 3.5 degrees in declination and spanning the full range of right ascension. In the 2004-05 observing season the calibration runs were taken at elevations of 86 degrees and 83 degrees. Beginning in the 2005-06 season, the nightly calibration runs were taken at an elevation of 80 degrees. Collectively, these drift scans cover a strip approximately 12.5 degrees wide in declination, centered at declination 37.18 degrees, and spanning the full range of RA. The analysis procedures developed for drift scan data, the sensitivity of the method, and the results will be presented.

Contribution to the 30th International Cosmic Ray Conference, Merida, Mexico, July 2007

astro-ph/0709.4195

  VERITAS is a system of four imaging Cherenkov telescopes located at the Fred Lawrence Whipple Observatory in southern Arizona. We present here results of detailed Monte Carlo simulations of the array response to extensive air showers. Cherenkov image and shower parameter distributions are calculated and show good agreement with distributions obtained from observations of background cosmic rays and high-energy gamma-rays. Cosmic-ray and gamma-ray rates are accurately predicted by the simulations. The energy threshold of the 3-telescope system is about 150 GeV after gamma-hadron separation cuts; the detection rate after gamma-selection cuts for the Crab Nebula is 7.5 gamma's/min. The three-telescope system is able to detect a source with a flux equivalent to 10% of the Crab Nebula flux in 1.2 h of observations (5 sigma detection).

Contribution to the 30th International Cosmic Ray Conference, Merida, Mexico, July 2007

astro-ph/0709.4517

  VERITAS is a new atmospheric Cherenkov imaging telescope array to detect very high energy gamma rays above 100 GeV. The array is located in southern Arizona, USA, at an altitude of 1268m above sea level. The array consists of four 12-m telescopes of Davies-Cotton design and structurally resembling the Whipple 10-m telescope. The four focal plane instruments are equipped with high-resolution (499 pixels) fast photo-multiplier-tube (PMT) cameras covering a 3.5 degree field of view with 0.15 degree pixel separation. Light concentrators reduce the dead-space between PMTs to 25% and shield the PMTs from ambient light. The PMTs are connected to high-speed preamplifiers allowing operation at modest anode current and giving good single photoelectron peaks in situ. Electronics in the focus box provides real-time monitoring of the anode currents for each pixel and ambient environmental conditions. A charge injection subsystem installed in the focus box allows daytime testing of the trigger and data acquisition system by injecting pulses of variable amplitude and length directly into the photomultiplier preamplifiers. A brief description of the full VERITAS focal plane instrument is given in this paper.

Contribution to the 30th International Cosmic Ray Conference, Merida, Mexico, July 2007

 A probability density method for VHE gamma-ray source analysis, applicable to both stand alone IAC telescopes and stereoscopic arrays, is presented here. Developed using simulations and Crab data for the Whipple 10m telescope, the technique covers both two-dimensional image and spectral analyses, and background subtraction is implemented either by a modified standard approach using cuts on Hillas parameters, or by a kernel multivariate analysis. The probabilistic method adopted can also be extended into a log likelihood technique where data characteristics such as source strength, extension, or multiple sources within the field of view can be determined.