03-18-04

IOWA STATE UNIVERSITY ASTROPHYSICISTS SHARE $17.5 MILLION AWARD TO GO AFTER GAMMA RAYS

AMES, Iowa -- Several Iowa State University scientists play a major role in the upcoming construction of VERITAS (VeryEnergetic Radiation Imaging Telescope Array System), an array of telescopes designed to pursue major advancements ingamma-ray astronomy.

A total of $17.5 million has been awarded to the project by the U.S. Department of Energy and the National ScienceFoundation. VERITAS will consist of four optical reflectors, similar to telescopes, each equipped with 350 mirrorfacets to create a 12-meter aperture. A 499-pixel camera will be located in the focal plane of each telescope as well.This combination of equipment will form one of the most sensitive, high-energy gamma-ray observatories in theworld.

Frank Krennrich, associate professor of physics and astronomy, leads the ISU group in the design and construction ofthe focal plane cameras. A prototype camera, about the size of a hot tub, was built recently on the ISU campus. It isnow being used and tested in the prototype telescope at the Whipple Observatory in Arizona.

The ISU scientists also are constructing the electronics that are located inside the cameras. This system will allowscientists to take measurements of faint light flashes lasting a few billionths of a second, Krennrich said.Collaborating with him on the ISU project from physics and astronomy are professor David Carter-Lewis, assistantprofessor Martin Pohl, postdoctoral students Stephane Le Bohec and Michael Daniel, and graduate students Bagmeet Beheraand Asif Imran, as well as Patrick Jordan, a senior majoring in mathematics.

VERITAS will be located on a 25-acre site in the Horseshoe Canyon at Kitt Peak Observatory in Arizona. Constructionbegins on the site this spring. The telescope array, which will stand about 5,800 feet above sea level, is projectedfor completion in October 2006. Other institutions collaborating on VERITAS include Harvard-Smithsonian Center forAstrophysics, Purdue University, Washington University, University of Chicago, University of Utah, University ofCalifornia-Los Angeles, McGill University, National University of Ireland and University of Leeds, UnitedKingdom.

Scientists involved in the project point to VERITAS as an important step forward in the study of extreme astrophysicalprocesses in the universe. The instruments will utilize the power of the Cherenkov imaging technique, pioneered in theearly 1980s at the Whipple Observatory by a group of scientists from ISU, Harvard-Smithsonian and the University ofIreland, including Carter-Lewis and Richard Lamb, now professor emeritus. This technique, using a 10-meter opticalreflector built in 1968, detected so-called TeV gamma rays that have energies more than a trillion times the energy ofvisible light. These gamma rays interact with atoms in the upper atmosphere and initiate a cascade, or shower, ofparticles. These showers lead to a short burst of blue light. Using arrays of fast photo-detectors at the focus of thelarge optical reflector, the Whipple group recorded the image of the cascade of particles, and showed that they couldidentify those initiated by gamma rays from the much more numerous background produced by charged cosmic rays.

Using this technique, the Whipple collaboration detected the first source of TeV gamma rays in the galaxy in 1989,known as the Crab Nebula, a supernova remnant, and the first extragalactic source in 1992, Markarian 421, an activegalactic nucleus or quasar.

VERITAS will combine the Cherenkov imaging technique with the power of stereoscopic measurements, using an array oftelescopes looking at the same shower. According to Krennrich, the telescopes will take rapid snapshots of the faintglows that last billionths of a second. "Instead of just observing from one direction, as with the old 10-metertelescope, all the cameras can look at the same shower from various viewpoints on the ground, providing us with muchmore precise information of the shower," he said.

VERITAS will have a sensitivity that exceeds that of the Whipple telescope by a factor of 10, and it is anticipatedthat more than 100 sources will be detected. Those sources include pulsars, supernova remnants, x-ray binaries, blackholes, active galactic nuclei and gamma-ray bursts.

"For instance," Krennrich said, "there are many galaxies with massive black holes in their centers. These black holesproduce a beam that resembles that from a lighthouse, but that consists of high-energy radiation. This research mayhelp us understand how black holes convert energy into radiation."

"We'll be observing sources with physical conditions comparable to having the entire power output of the sun producedin a volume roughly the size of this 12-ounce juice bottle," Pohl added. Pohl studies cosmic rays, a particle radiationfirst detected more than 90 years ago but whose sources are still unknown.

The completion of the VERITAS construction is orchestrated to coincide with the 2007 launch of NASA's $300 millionGamma-ray Large Area Space Telescope (GLAST), the next large space-based gamma ray telescope, currently in constructionas well. The energy range accessible with GLAST will overlap that of VERITAS. This is the first time that space- andground-based telescopes will provide a continuous coverage of more than 20 octaves of the electromagnetic spectrum.Pohl, in his first year at Iowa State, serves as an interdisciplinary scientist for the GLAST project. His appointmentto ISU makes the university the only U.S. institution to employ scientists involved in both experiments of high-energygamma-ray research.

"People built radio telescopes in the 1950s, and X-ray telescopes in the 1970s, and these have substantially broadenedour view of the universe," Krennrich said. "Now we will be using a new wavelength regime to find exciting phenomena atthe high-energy frontier of the electromagnetic spectrum."

"What we have been observing optically from many sources is, as far as the power output is concerned, just peanuts,"Pohl added. "Gamma rays are the only way to really understand what is happening out there. It's my hope that we canactually begin to understand these sources that have been complete surprises to past researchers."

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