Oct. 19, 2000
Vol. 20 No. 3

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    HETE-2 looks for gamma-ray bursts

    By Steve Koppes
    News Office

    NASA’s newly launched High Energy Transient Explorer-2 satellite will help University scientists seek out and understand gamma-ray bursts, the most powerful explosions in the known universe.

    University scientists who will play a key role in the four-year mission said they hope HETE-2 will lead them to the most distant objects in the known universe and thus, to new insights into the formation of the first stars and galaxies.

    Image courtesy of MIT
    HETE-2 is the replacement mission for the original HETE satellite that was lost in 1996 following a rocket malfunction. It is the first satellite dedicated to the study of gamma-ray bursts. It also has faster reflexes than any other gamma-ray detecting satellite currently in orbit and is able to pinpoint burst locations within seconds for making crucial follow-up observations.

    “The universe is so rich that anytime you have an instrument or a satellite with a capability several times better than ever before, you come upon completely unexpected or unpredicted phenomena that knock your socks off,” said Don Lamb Jr., Professor in Astronomy & Astrophysics. Lamb helped develop the mission concept and serves as a member of HETE’s international science team, which is led by George Ricker at the Massachusetts Institute of Technology.

    For much of the last three decades, gamma-ray bursts have ranked among the greatest mysteries of astronomy. Only recently have scientists produced evidence linking the longest of these bursts to supernovas, which result from the collapse of massive stars.

    Lasting anywhere from fractions of a second to many minutes and packing the power output of as many as 1,000 supernovas, these unpredictable bursts occur almost daily and come from any direction in the sky. The bursts are followed by afterglows, which are visible for a few days at X-ray and optical wavelengths. HETE-2 was specially designed to observe afterglows.

    “In the past, mysterious and exotic phenomena have been understood by finding their optical counterparts,” Lamb said. In May, the Compton Gamma-ray Observatory ended a highly successful mission that began in 1991, but it was unable to precisely locate burst positions for analysis by optical telescopes.

    HETE-2’s onboard computers, by contrast, will rapidly calculate the position of a newly detected burst and relay the data to ground stations, where it will be available immediately to astronomers worldwide for simultaneous and follow-up observations.

    Astronomers hope HETE-2 will quickly find a burst that went off when the universe was quite young, no more than a billion years old. Such bursts could help cosmologists unravel the origins of the universe, Lamb said.

    “Probably the second-most important thing we hope to get out of it is a short burst, one of less than a second,” said Daniel Reichart, a California Institute of Technology astronomer who completed his Ph.D. at the University earlier this year. “It’s still a mystery what causes these things. We hope to shed some light on that.”

    HETE-2 was launched Monday, Oct. 9, via a Pegasus rocket from the Kwajalein Missile Range in the Marshall Islands of the South Pacific. “It was a flawless launch,” said Carlo Graziani, a Research Scientist in Astronomy & Astrophysics and a member of the Chicago HETE-2 team.

    Planning for the original HETE began in the 1980s and served as a forerunner of the “faster, better, cheaper” type of mission advocated by NASA Administrator Daniel Goldin.