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University Communications
University of Wisconsin-Madison

CONTACT:
Eric Wilcots, (608) 262-2364, ewilcots{at}astro.wisc.edu
Ramotholo Sefako, (608) 262-4409, sefako{at}astro.wisc.edu
Terry Devitt, (608) 262-8282, trdevitt{at}wisc.edu

FOR IMMEDIATE RELEASE: 5/28/03

NEW TECHNIQUE NARROWS HUNT FOR GAMMA-RAY BLAZARS

NASHVILLE -- In the quest to peel back the mysteries of some of the
most compelling physics in the cosmos, the enigmatic high-energy
gamma-ray blazar -- a jet spouting from a giant black hole --
promises new insight into some astrophysical phenomena that,
tantalizingly, seem to be just beyond the grasp of astronomers.

But pinpointing such blazars with ground-based gamma-ray telescopes,
the kind of telescope that might reveal some of the tightly held
secrets of the rare, very high-energy gamma-ray species of blazar, is
a difficult, highly inefficient process. Few are known.

Now, however, thanks to new optical techniques developed by a team of 
astronomers at the University of Wisconsin-Madison, the world's
gamma-ray telescopes may be able to quickly zoom in on this unusual
type of blazar instead of wasting valuable telescope time searching
the skies for their telltale signatures.

In general, blazars are a class of information-rich objects that can
shine across the electromagnetic spectrum -- from radio to very
high-energy gamma rays in some cases. In the optical, most look very
much like a star, a simple point of light in the sky. Most blazars
are found at cosmological distances, billions of light years away.

A species that may be especially rich in information is known as the
TeV gamma-ray blazar because it emits gamma rays at extremely high
energies. Some of these high-end blazars are relatively close at
hand, a mere 300 million light years from Earth. But when gamma-ray
telescopes scan the sky, they have a hard time homing in on the point
sources that may be emitting the gamma rays. 

"With gamma-ray telescopes, you can observe a source for three months
before you get a signal," says Ramotholo Sefako, a UW-Madison
astronomer who, with Wisconsin colleague Eric Wilcots, today (May 28)
presented research results that could make it far easier for
astronomers to find TeV blazars. With these new techniques, "we can
tell which objects are likely to be high-energy objects. Our aim is
to correlate optical and gamma-ray results," Sefako says. 

The astronomers, who used the 1.0-meter telescope at the South
African Astronomical Observatory, shared their findings at the 202nd
meeting of the American Astronomical Society in Nashville. The team
presented results on observations of eight objects and described
optical techniques that would cut the identification time for a
high-energy blazar from three months to a day.

The ability to quickly home in on blazars emitting gamma rays at TeV
energies using ground-based optical telescopes promises a wealth of
new objects for study by astronomers using gamma-ray telescopes. With
more known high-energy gamma ray blazars to choose from, astronomers
can use scarce gamma-ray telescope time to study what are considered
to be some of the most unusual objects in the cosmos instead of
spending time combing the skies for them. 

Blazars exist at the cores of galaxies. And while no one knows for
sure what lies at their cores, current thinking is that an enormous
black hole -- perhaps a billion times more massive than the sun --
creates light-years-long jets of plasma that stick out from the poles
of a torus created by an accreting disk of material spinning into the
black hole. It is these jets that are believed to be the source of
the high-energy gamma rays that interest astronomers. 

Viewed at the right angle, blazars could provide a unique window to a
black hole, says Wilcots: "The jet may be a way to get a look right
down to the core, a view that is otherwise obscured by the torus of
these objects." 

An ability to drill down to the core of these objects, Sefako notes,
may yield insight into the physics of black holes, including a more
detailed understanding of accretion disks behavior, the physics of
the jets themselves and perhaps even be the key to discovering the
origin of cosmic rays.

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