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

abs/0709.3695

  Observations of the blazars 1ES 0647+250 and 1ES 0806+524 with VERITAS are reported here. These objects are among the favoured candidate extragalactic sources in the very high-energy regime due to the presence of high-energy electrons and adequate seed photons. The presence of high-energy electrons is established from the location of the synrchrotron peak in the spectral energy distribution of the blazars. The presence of adequate seed photons is determined by the flux in the radio-through-optical wavebands. These are the key ingredients for very high-energy gamma-ray emission in the context of the synchrotron self-Compton model. The redshift of 1ES 0647+250 has been tentatively reported as 0.203 and the redshift of 1ES 0806+524 is 0.138, thus the detection of very high-energy gamma-ray emission from these objects could make significant contributions to the understanding of the extragalactic infrared background light. The analysis of these data relies on standard techniques in very high-energy gamma-ray astronomy, and the results are compared to previously reported upper limits and to theoretical predictions.

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

abs/0709.4208

  Abstract: VERITAS employs a 12m segmented mirror and pixellated photomultiplier tube camera to detect the brief pulse of Cherenkov radiation produced by the extensive air shower initiated by a cosmic high-energy gamma ray. The VERITAS data acquisition system consists of a 500 Mega-Sample-Per-Second custom-built flash ADC system, which samples the Cherenkov light pulse every 2 nanoseconds. The integrated charge in each flash ADC channel is proportional to the amount of Cherenkov light incident on the corresponding photomultiplier tube. Accurate reconstruction of the integrated charge is required for accurate energy estimation and spectral reconstruction. A reliable calculation of the integrated charge at low intensities can lead to a reduction in the energy threshold of the system, and an increase in sensitivity. This paper investigates and compares several approaches for evaluating the integrated charge. The Cherenkov pulse timing information in the flash ADC readout has the potential to assist in background rejection techniques. Various methods for extracting the timing information are investigated and excellent timing resolution is achieved.

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

abs/0709.4233

  VERITAS, the Very Energetic Radiation Imaging Telescope Array System, is an array of four 12 m diameter imaging atmospheric Cherenkov telescopes for gamma-ray astronomy above 100 GeV currently in operation in Arizona. The VERITAS Collaboration has developed VEGAS, the VERITAS Gamma-ray Analysis Suite, a data-analysis software package for the processing of single- and multiple-telescope data produced by the array. The package consists of a core of six stages as well as visualisation and diagnostic components. It has been developed in C++ using modern objected-oriented design patterns to be highly flexible, configurable and extendable. VEGAS utilises CERN's ROOT data-analysis framework and runs on Linux and Mac OS X systems. The architecture and structure of the VEGAS package will be described in detail while the data analysis algorithms are described in additional papers.

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

abs/0709.4006

  VERITAS is an array of Imaging Atmospheric Cherenkov Telescopes designed for very high energy gamma ray (E>100,GeV) observations of astrophysical sources.
The experiment began its scientific observation program in the 2006/2007 observing season. We describe here the analysis chain for reducing the data, reconstructing the direction and energy of incident gamma rays and the rejection of background cosmic rays.