May 15, 2003 – Vol. 22 No. 16

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    Chicago astrophysicist analyzing data from rare gamma-ray burst

    By Steve Koppes
    News Office

    An artist’s conception of the violent blast of gamma rays emitted by the recent GRB030329 in the constellation Leo is shown above. Gamma ray bursts are explosions so powerful that they can be seen across billions of light-years of space, emitting 10 times as much energy in a few seconds as the sun will release in its entire 10-billion-year lifetime.
    The birth cry of a black hole has startled Chicago astrophysicists and their colleagues who operate a NASA satellite that searches for gamma-ray bursts, the most powerful explosions in the universe.

    The Saturday, March 29 explosion occurred approximately 2 billion light years from Earth, too distant to pose a threat, but two and a half times closer than the next-closest burst for which scientists have reliable measurements.

    “The chance of a burst this near and this bright happening is one in a few thousand,” said Don Lamb Jr., the Louis Block Professor in Astronomy & Astrophysics and the Mission Scientist for NASA’s High-Energy Transient Explorer-2 satellite. If such bursts are evenly distributed throughout the universe, he said, “we won’t see anything like this again.”

    Follow-up observations by scientists at the Harvard-Smithsonian Center for Astrophysics quickly and, for the first time, clearly linked gamma-ray bursts and supernovae, which are exploding stars. This type of supernova results in the formation of a black hole, a compact object so dense that no light can escape its gravitational pull.

    Lamb and his associates then confirmed the center’s finding using the Astrophysical Research Consortium 3.5-meter telescope at Apache Point Observatory in New Mexico.

    “There have been clues and hints that gamma-ray bursts might be produced by core-collapse supernovae, but now it’s certain,” Lamb said.

    The data suggest that the supernova explosion was non-spherical, which supports new ideas about how core collapse supernovae happen. “This is absolutely going to change everything,” Lamb said.

    The cause of gamma-ray bursts has perplexed astrophysicists for the last three decades. Lasting anywhere from fractions of a second to many minutes, these unpredictable bursts occur almost daily and come from any direction in the sky. Afterglows, which are visible for a few days at X-ray and optical wavelengths, follow these bursts. HETE-2, launched in 2000, pinpoints burst locations within seconds so that ground telescopes can make crucial follow-up observations.

    The Saturday, March 29 burst lasted for more than 30 seconds. During this time it outshined the entire universe in gamma-ray emissions. Only two out of nearly 3,000 gamma-ray bursts that have been observed so far have shined more brightly since scientists discovered the phenomenon 30 years ago. Even the burst&s afterglow shined more than 10,000 times brighter than its host galaxy two hours after the burst occurred.

    “The supernova component continues to outshine the host galaxy,” Lamb said. He expects that several more weeks will pass before the afterglow fades enough for astronomers to spot the host galaxy.

    Once the afterglow fades for good, it will have brought together a marriage between the gamma-ray burst and supernova fields.

    “The fields have been engaged for years now, but today I’m in the happy circumstance of witnessing them saying, ‘I do,” Lamb said.

    Collaborating with Lamb on HETE-2 are Carlo Graziani, Senior Research Associate in Astronomy & Astrophysics, and Timothy Donaghy, a graduate student in Physics. Collaborating with him on the follow-up observations are Donald York, the Horace B. Horton Professor in Astronomy & Astrophysics and the College, and John Barentine, Russet McMillan, Jack Dembicky and Bill Ketzeback, observing specialists at Apache Point Observatory.