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

astro-ph/0709.4479

  VERITAS is an array of four identical telescopes designed for detecting and measuring astrophysical gamma rays with energies in excess of 100 GeV. Each telescope uses a 12 m diameter reflector to collect Cherenkov light from air showers initiated by incident gamma rays and direct it onto a `camera' comprising 499 photomultiplier tubes read out by flash ADCs. We describe here calibration methods used for determining the values of the parameters which are necessary for converting the digitized PMT pulses to gamma-ray energies and directions. Use of laser pulses to determine and monitor PMT gains is discussed, as are measurements of the absolute throughput of the telescopes using muon rings.

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

astro-ph/0710.2288

  VERITAS employs a multi-stage data acquisition chain that extends from the VME readout of custom 500 MS/s flash ADC electronics to the construction of telescope events and ultimately the compilation of information from each telescope into array level data. These systems provide access to the programming of the channel level triggers and the FADCs. They also ensure the proper synchronization of event information across the array and provide the first level of data quality monitoring. Additionally, the data acquisition includes features to handle the readout of special trigger types and to monitor channel scaler rates. In this paper we describe the software and hardware components of the systems and the protocols used to communicate between the VME, telescope, and array levels. We also discuss the performance of the data acquisition for array operations.

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

astro-ph/0709.3977v1

  As a calibrated laser pulse propagates through the atmosphere, the amount of Rayleigh-scattered light arriving at the VERITAS telescopes can be calculated precisely. This technique was originally developed for the absolute calibration of ultra-high-energy cosmic-ray fluorescence telescopes but is also applicable to imaging atmospheric Cherenkov telescopes (IACTs). In this paper, we present two nights of laser data taken with the laser at various distances away from the VERITAS telescopes and compare it to Rayleigh scattering simulations.

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.