The University of Utah Gamma Ray Group is funded by National Science Foundation Grant # PHY0555451


Data Analysis

The Utah group provides primary and secondary analysis with the GrISU analyis package. To view our most recent results go to the internal wiki page.

Construction and Calibration


Apart from building telescope electronics and hardware, we also run simulations to find out how the telescope will respond under different circumstances. Extensive work has been done to simulate showers generated by various charged particles and gammarays in order to accurately distinguish the images of the two types as seen in the telescope camera. Also, sky glow and cosmic ray backgrounds have been simulated to test the effectiveness of the triggering systems.


A calibrated laser pulse propagating through the atmosphere produces a flash of Rayleigh scattered light with an intensity that can be calculated precisely when atmospheric conditions are good. This is originally developed for the absolute calibration of ultra high energy cosmic ray flurorescence telescopes and we have implemented it to our own absolution calibration system for Imaging Atmospheric Cherenkov telescopes.

We mounted a nitrogen laser onto a movable rack that can be taken down the road to various distances away from the telescopes. Rayleight scattering simulation program is written by Nathan Shepherd, who also built the road laser prototype. We record the atmospheric conditions of the night road laser data is taken and use them as parameters for the simulation. We then compare how well the data matches the simulation to determine how well the telescopes are operating compare to their specifications.

N.Shepherd et al, Absolute calibration of imaging atmospheric Cherenkov telescopes, 29th ICRC Pune (2005) 00,101-106

Trigger Electronics

The VERITAS Telescope uses state of the art electronics to determine which signals are considered noise, and which are significant. At the heart of the triggering system is the Constant Fraction Descriminator (CFD). The CFD does not simply evaluate a signals height, but also evaluates the pulse width at a certain fraction of the height. This alows signals with low pulse heights compared to the night-sky background to be passed to the level two trigger.


The analog signals produced by the PMT's travel down the telescope arms, the mount, and to the electronics shed via RG-59 coaxial cable. Each telescope has one cable per PMT, so that means there is a lot of cabling to do. Not only do we measure and put connectors on each 150 foot cable, but we also test them to make sure that they have the same signal delay time. Along with testing the cables, we also have designed and implemented cable strain relief devices. These devices, found mostly in the telescope base, are designed to limit the amount of tension and twisting in the cables. To the right is a picture of a recorded wave form from on of the test cables and a photo of one of the cable strain relief systems in the telescope base.

Contact Us: gammaray (at) | ©2007 University of Utah Gammaray Group