SETI [ASTRO] Astronomy Experiment Opens New Window On High-Energy Gamma Rays

Larry Klaes (
Thu, 03 Jun 1999 11:12:19 -0400

>X-Authentication-Warning: majordom set sender to owner-astro using -f >Date: Wed, 2 Jun 1999 23:38:11 GMT >From: Ron Baalke <> >To: >Subject: [ASTRO] Astronomy Experiment Opens New Window On High-Energy Gamma Rays >Sender: >Reply-To: Ron Baalke <> > >University of Chicago News Office >5801 South Ellis Avenue - Room 200 >Chicago, Illinois 60637-1473 >(773) 702-8360 Fax: (773) 702-8324 > >Contact: Steve Koppes, (773) 702-8366, > >May 31, 1999 > >Astronomy experiment opens new window on high-energy gamma rays > >An innovative experiment that uses the Earth's atmosphere as a gamma-ray >telescope has successfully detected its first celestial object through a >window in the spectrum previously closed to astronomers, University of >Chicago physicists reported today at the American Astronomical Society's >centennial meeting in Chicago. > >The detection demonstrates the ability of the Solar Tower Atmospheric >Cherenkov Effect Experiment (STACEE) to view the gamma-ray spectrum >of the sky that ranges from approximately 10 billion electron volts to 300 >billion electron volts, said Chicago physicists Corbin Covault and Ren=E9= > Ong. >Neither the orbiting Compton Gamma-Ray Observatory nor ground-based >experiments have previously been able to detect gamma rays in this >energy range. Gamma rays contain vastly more energy than visible light >rays, which have the energy of one electron volt. > >"We have been running long enough to have a preliminary result on the >detection of an important source, the Crab Nebula, which we observed >several times since the fall," Covault said. The STACEE team will >announce more detailed results later this year following further analysis. > >"STACEE is a new experiment that does something completely different >from anything that's ever been done before, doing high-energy astronomy >using gamma rays," Ong said. The project contributes to the growing field >of high-energy astronomy, which applies techniques used in particle >physics experiments to the study of celestial phenomena. > >Other objects that STACEE will view in the future may derive their >power from supermassive black holes, neutron stars or other objects >that generate high-energy particles. "When an object emits these very >high-energy particles, they're doing something special," Ong said. "We >hope that it represents some type of new astrophysics or even perhaps >under extreme cases new physics that we couldn't generate here on Earth." > >STACEE detected the Crab Nebula, a remnant of an exploding star, using >half the apparatus that it will eventually have. Once construction is >complete in early 2000, the experiment will be five to 10 times more >sensitive to celestial objects than it is now. > >"It will allow us to look further out into the universe," Ong said. "The >Crab Nebula is in our galaxy. It's about 6,000 light years away. The other >objects that we're interested in are quasar-like objects, believed to be >driven by supermassive black holes, which might be millions or billions >of light years away. By getting better sensitivity, we'll be able to see >more of those as well." > >STACEE operates at the National Solar Thermal Test Facility at Sandia >National Laboratories in Albuquerque, N.M. By day, the facility's array of >220 large mirrors, called heliostats, are used to track and focus sunlight >for solar energy research. On dark, moonless nights, the STACEE >collaboration uses some of those mirrors to collect tiny flashes of blue >light known as Cherenkov radiation, which gamma rays produce when they >enter Earth's atmosphere. > >The heliostats, each measuring 20 feet by 20 feet, collect the radiation >and focus it on a 200-foot central tower. Secondary mirrors mounted on >the tower image the radiation onto sensitive light detectors. > >"We don't have to send anything to space. We don't simply look at light >coming down through the atmosphere. We use the whole atmosphere as >our Cherenkov detector," Ong said. > >The Crab Nebula detection was achieved using only 32 heliostats, 32 >photodetectors and their associated electronics. Another 32 heliostats >and improved electronics will be added by early 2000. > >"The part of the experiment that we construct are the optics that sit >on the tower, the associated photodetectors and all the associated >electronics," Covault said. "For each heliostat that you wish to collect >light from you have to build the appropriate additional materials." > >Covault and Ong built STACEE in collaboration with a team of 20 >scientists at Chicago and at McGill University in Canada; the University >of California, Santa Cruz; the University of California, Riverside; and >Barnard College and Columbia University. > >The $1 million STACEE project is funded by the National Science >Foundation and makes use of the National Solar Thermal Test Facility >through a cooperative agreement with the U.S. Department of Energy. >STACEE's collaborators at McGill University received additional >funding from the National Sciences and Engineering Research Council >of Canada. >

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