Team Led by Penn State Astronomer Records Spectra of Gamma-Ray Burst
12 December 2002 -- A team of astronomers led by Penn State's Michael Eracleous, assistant professor of astronomy and astrophysics, has used the Hobby-Eberly Telescope to help measure the spectrum of a gamma-ray burst, one of only a dozen such detailed measurements ever recorded out of the thousands of gamma-ray bursts detected by spaced-based observatories.
"To understand the nature of gamma-ray bursts we need to determine how energetic they are, which, in turn, means that we need to measure their distances," Eracleous said. "To do this we must obtain spectra of the bursts while they are still bright -- before they fade to invisibility after a day or two. This is a challenging task because it requires the coordinated effort of many astronomers around the world and several telescopes on Earth and in space."
Gamma-ray bursts are the most powerful known explosions in the universe. "For a few seconds, the intensely brilliant flashes of gamma radiation outshine every other object in the sky -- at gamma ray, X-ray, and visible wavelengths -- and can be detected all the way to edge of the observable universe," commented Peter Mészáros, Distinguished Professor and head of Penn State's Department of Astronomy and Astrophysics. Mészáros is one of the leaders in the effort to understand the mysterious underlying cause of the explosion that results in gamma-ray bursts. Possibilities include the formation of a black hole at the end of the life of a massive star or the coalescence of two neutron stars that have been circling each other for hundreds of millions of years, themselves remnants of an earlier generation of massive stars.
Eracleous' team includes Penn State professor Steinn Sigurdsson, Mészáros, and astronomers at the University of Texas, Stanford University, and the German universities Georg-August-Universität Göttingen and Ludwig-Maximilians-Universität München. The team has tried twice previously to take spectra of gamma-ray bursts, but the measurements were not of sufficient quality to gauge the distance of the explosions from Earth.
Because time is so critical and coordination is so intricate in observing the fleeting gamma-ray bursts, the team has set up a hi-tech strategy to coordinate its efforts, including an electronic notification service that sends alerts about gamma-ray bursts. Eracleous also is alerted through his cell phone so that he is able to respond quickly. If the gamma-ray team is able to observe the gamma-ray burst, the scientists notify the resident astronomers at the Hobby-Eberly Telescope directly to give them instructions on how to carry out the observations. Immediately after the observations are made, Eracleous retrieves the data via the Internet, analyzes the data, and reports the results in an electronic circular, which is immediately distributed around the world by e-mail. "The queue scheduling of the Hobby-Eberly Telescope allows one to immediately assign a high priority to this type of observation, for which speed is of the essence," said Penn State professor Larry Ramsey, the Hobby-Eberly Telescope Project Scientist.
"We are about to enter a very active new phase of gamma-ray burst research with the launch next year of the Swift Gamma-Ray Burst Explorer," noted Eracleous, referring to NASA's gamma-ray satellite that is being built as a joint project with the Goddard Space Flight Center and Penn State and will be controlled from the University Park campus. "We expect to receive several gamma-ray-burst alerts each week, and the Hobby-Eberly Telescope will play an important role in future investigations of this spectacular phenomenon."
The Hobby-Eberly Telescope is a joint project of The University of Texas at Austin, Penn State, Stanford University, Ludwig-Maximilians-Universität München, and Georg-August-Universität Göettingen. The namesakes of the telescope are William P. Hobby, the former Lieutenant Governor of Texas, and Robert E. Eberly of Pennsylvania, an industrialist and philanthropist. The telescope stands on Mount Fowlkes at the McDonald Observatory in far West Texas, which has the darkest skies of any major observatory in the continental United States.