Monday, April 23, 2007

Veritas & Gamma Rays

The four telescopes of the VERITAS system at the Fred Lawrence Whipple Observatory in Arizona create the northern hemisphere's most sensitive instrument for finding gamma rays from space. Photo by S. Criswell, VERITAS Project.

The $20 million VERITAS telescope system - that's the Very Energetic Radiation Imaging Telescope Array System - at the Fred Lawrence Whipple Observatory south of Tucson, is made of four reflectors 12 meters across that look like satellite dishes. The reflectors are covered with mirrors that direct light into cameras attached to the front of each dish. Each camera is about 7 feet across and contains 500 tube-shaped photon detectors or pixels.

Each of the four VERITAS cameras created by Iowa State researchers contains 500 photon detectors that can see particle showers created by gamma rays hitting the earth's atmosphere.
Photo contributed by Frank Krennrich

VERITAS is the northern hemisphere's most sensitive instrument for finding that high energy electromagnetic radiation. And gamma rays do have lots of energy: the energy of visible light is one electron volt; gamma rays have energies of 1 million to 1 trillion electron volts.

Even with all that energy, the rays can't penetrate the earth's atmosphere. But when they hit the atmosphere they create showers of electrons and positrons that create a blue light known as Cerenkov radiation. The showers move very fast. And they're not very bright.

So it takes a powerful instrument to find them. The astronomers say VERITAS is proving to be as sensitive as they expected.

Astrophysicists now know that gamma rays are produced by supermassive black holes, supernova remnants, pulsars, gamma ray bursts and other space objects.

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