Two billion years ago, in a far-away galaxy, a giant
star exploded, releasing almost unbelievable amounts of energy as it
collapsed to a black hole. The light from that explosion finally reached
Earth at 6:37 a.m. EST on March 29, igniting a frenzy of activity among
astronomers worldwide. This phenomenon has been called a hypernova, playing
on the name of the supernova events that mark the violent end of massive
stars.

With two telescopes separated by about 110 degrees longitude, the Robotic
Optical Transient Search Experiment (ROTSE) will have one of the most
continuous records of this explosion.

“The optical brightness of this gamma ray burst is about 100 times more
intense than anything we’ve ever seen before. It’s also much closer to us
than all other observed bursts so we can study it in considerably more
detail,” said Carl W. Akerlof, an astrophysicist in the Physics Department
at the University of Michigan. Akerlof is the leader of ROTSE, an
international collaboration of astrophysicists using a network of
telescopes specially designed to capture just this sort of event. The
collaboration is headquartered at U-M and funded by NASA and the National
Science Foundation (NSF).

Just recently, the ROTSE group commissioned two optical telescopes in
Australia and Texas and were waiting for the first opportunities to use the
new equipment. The burst was promptly detected by NASA’s Earth orbiting
High-Energy Transient Explorer (HETE-2) but human intervention was required
to find the exact location. Despite sporadic clouds and rainstorms in
Australia, the ROTSE instrument at Siding Spring Observatory in northern
New South Wales was able to record the decaying light from the blast.
Twelve hours later, the second ROTSE telescope in Fort Davis, Texas was
picking up the job of monitoring this spectacular explosion.

“During the first minute after the explosion it emitted energy at a rate
more than a million times the combined output of all the stars in the Milky
Way. If you concentrated all the energy that the sun will put out over its
entire 9 billion-year life into a tenth of a second, then you would have
some idea of the brightness,” said Michael Ashley, faculty member in the
astrophysics and optics department at the University of New South Wales and
a member of the ROTSE team.

Akerlof became interested in studying gamma ray bursts in the early 1990s.
While they are the most powerful explosions in the universe, gamma-ray
bursts are extremely hard to study because they are extremely distant,
occur randomly in time and seldom last more than a minute. Small, fast, and
relatively inexpensive robotic ground-based telescopes like ROTSE offer the
best chance of catching early optical emissions from the bursts. ROTSE
attracted national notice in 1999 when it captured the rise and fall of
GRB990123, one of the brightest bursts prior to this latest event.

“The ROTSE equipment is quite modest by modern standards, but its wide
field of view and fast response allow it to make measurements that more
conventional instruments cannot,” Akerlof said. “We have two telescopes
online now, and installations in Namibia and Turkey will follow soon. Our
goal is to have telescopes continuously trained on the night sky. Our motto
is ‘The Sun never rises on the ROTSE array.’ That’s why we want them
spread as widely as possible.”

Another role for ROTSE and other small telescopes is to alert larger
facilities about gamma ray bursts and other transient phenomena. “One of
the most exciting things about an event like this is the way the global
community of scientists pulls together, pooling their data and their
different capabilities,” Akerlof said.

For more information about ROTSE, visit http://www.rotse.net. To learn more
about physics at the U-M visit http://www.physics.lsa.umich.edu. For more
about Carl Akerlof, see
http://www.physics.lsa.umich.edu/department/directory/bio.asp?ID=3D5.