Historic GRB Discovery

Data supporting the April 10 announcement first linking the discovery of the March 29 gamma-ray burst to a supernova 2,650 million light-years away will be published in the July 1 issue of The Astrophysical Journal Letters. The discovery was made by Harvard-Smithsonian Center for Astrophysics (CfA) astronomers Dr. Thomas Matheson and Dr. Kryzstof Stanek, and Dr. Peter Garnavich of Notre Dame.

The team began analyzing data from the March 29 blast a mere fourteen hours after the event using the 6.5-meter MMT telescope at Mount Hopkins in Arizona. That data, in the best tradition of crime scene investigations so popular on TV today, linked the gamma-ray burst event with the detection of the ensuing supernova.

"There should no longer be doubt in anybody's mind that gamma-ray bursts and supernovae are connected," said Matheson, a member of the team that made this discovery.

The investigation began on March 29 when NASA's High-Energy Transient Explorer satellite (HETE) discovered one of the brightest and closest gamma-ray bursts on record.

Located in the constellation Leo, the 30-second burst outshone the entire Universe in gamma rays, and its optical afterglow was still over a trillion times brighter than the Sun two hours later.

Gamma-ray bursts are incredibly bright flashes of high-energy radiation that likely signal the birth of black holes. Bursts occur at random locations scattered across the sky, and few last more than a minute, making them a challenge to study.

A supernova is the explosion of a star at least eight times as massive as the Sun. When such stars deplete their nuclear fuel, they no longer have the energy to support their mass. Their cores implode, forming either a neutron star or (if there is enough mass) a black hole.

"For the first time, we were measuring an event no other human beings had seen before, " said Stanek. "The MMT was our magic time machine that we used to capture this catastrophic cosmic event."

Matheson and the others have detected direct evidence that the burst afterglow's light is exhibiting the same patterns as light from a supernova. Namely, the scientists see changes in light absorbed by silicon and iron atoms (forged in the supernova) as the afterglow slowly fades away. The team is continuing to observe and analyze this unique burst.

Previous observations, particularly from NASA's Chandra X-ray Observatory controlled at the Harvard-Smithsonian Center for Astrophysics in Cambridge, MA, have provided convincing indirect evidence of the gamma-ray burst/supernova connection. Chandra detected iron and other heavy elements, which are formed in supernovae, in the vicinity of gamma-ray bursts.

"All gamma-ray bursts may have associated supernovae that are too faint to observe," Matheson said, "but this burst, named GRB 030329, was one of the closest known." "We caught it in the act," said Stanek.

The burst was approximately two billion light-years from Earth, as opposed to other bursts located upwards of 10 billion light-years away. Because the burst was both close and bright, the supernova was detectable.

"Our spectra are remarkably similar to the Type Ic 'hypernova' SN1998bw, meaning that the gamma-ray burst is clearly associated with a hypernova explosion - an event ten times more powerful than a typical supernova. We've seen such hypernova explosions in nearby galaxies, although without an accompanying powerful gamma-ray burst, so we'll be watching this distant explosion closely to see if it continues to fit the hypernova profile," said Garnavich.

The MMT is a joint venture of the Smithsonian Institution and the University of Arizona. The 6.5-meter-diameter optical telescope is located on the summit of Mt. Hopkins, the second-highest peak in the Santa Rita Range of the Coronado National Forest, approximately 30 miles south of Tucson, Arizona.

HETE was built by MIT as a mission of opportunity under the NASA Explorer Program, with collaboration among U.S. universities; Los Alamos National Laboratory; and scientists and organizations in Brazil, France, India, Italy and Japan.

High Resolution artwork image available at: http://www.cfa.harvard.edu/press/archive/pr0314image.html

The journal article reporting these results is available at: http://www.journals.uchicago.edu/ApJ/journal/issues/ApJL/v591n1/17299/17299.html

Stanek and Matheson first announced the emergence of the supernova spectrum in Gamma-Ray Burst Coordinates Network circular number 2107, online at: http://gcn.gsfc.nasa.gov/gcn3/2107.gcn3

Headquartered in Cambridge, Massachusetts, the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists organized into six research divisions study the origin, evolution, and ultimate fate of the universe.

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