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.
