April 6, 2005
In another first for the NASA-led space telescope mission called
Swift, five months into its mission it measured the distance to two
gamma-ray bursts (GRB), back to back, from opposite parts of the sky.
The GRB's are over nine billion light years away from the Earth.
The measurements were obtained utilizing the Ultraviolet/Optical
Telescope (UVOT).
"Swift will detect more gamma-ray bursts than any satellite that has
come before it, and now will be able to pin down distances to many of
these bursts too," said Peter Roming, UVOT Lead Scientist at Penn
State. "These two aren't distance record-breakers, but they're
certainly from far out there. The second of the two bursts was bright
enough to be seen from Earth with a good backyard telescope."
The Swift science team said these types of distance measurements
will become routine, allowing scientists to create a map to understand
where, when and how these brilliant, fleeting bursts of light are
created.
Gamma-ray bursts, the most powerful
explosions known in the Universe, are thought to signal the birth of
black holes; either from a massive star explosion or a merger of
smaller black holes or neutron stars. Several
appear each day from Earth's vantage point. They are difficult to
detect and study because they occur randomly from any point in the sky
and last only a few milliseconds to about a minute.
Swift, with three telescopes, is designed to detect bursts and turn on
its own to focus its telescopes, within seconds, on the burst
afterglow, which can linger for hours to weeks. The UVOT is a joint
product of Penn State University and the Mullard Space Science Laboratory in
England.
Swift detected the bursts on March 18 and 19, as indicted in their
names: GRB 050318 and GRB 050319. The UVOT team estimated that the
redshifts are 1.44 and 3.24, respectively, which corresponds to
distances of about 9.2 billion and 11.6 billion light years. (The
second estimate reflects a more precise measurement made with the
ground-based Nordic Optical Telescope.)
Distance measurements are attained through analysis of the burst
afterglow.
Swift detected 24 bursts so far. GRB 050318 was the first burst
where the UVOT detected an afterglow. The lack of afterglow detection
is interesting in its own right, Roming said, because it helps
scientists understand why some bursts create certain kinds of
afterglows, if any. For example, Swift's X-Ray
Telescope (XRT) has detected afterglows from several bursts. The UVOT
detected afterglows in GRB 050318 and GRB 050319 in optical light, but
not significantly in ultraviolet.
"Every burst is a little different, and when we add them all up we
will begin to see the full picture," said Keith Mason, the U.K. UVOT
Lead at University College London's 
Mullard Space Science Laboratory.
Mason said UVOT distance measurements will become more precise in
the upcoming months as new instruments aboard Swift are employed.
Swift is a medium-class explorer mission managed by NASA Goddard Space
Flight Center in Greenbelt, Maryland. Swift is a NASA mission with
participation of the Italian Space Agency and the Particle Physics and
Astronomy Research Council in the United Kingdom. It was built in
collaboration with national laboratories, universities and
international partners, including Penn State; Los Alamos National
Laboratory in New Mexico; Sonoma State University in California; the
University of Leicester in Leicester, England; the Mullard Space
Science Laboratory in Dorking, England; the Brera Observatory of the
University of Milan in Italy; and the ASI Science Data Center in Rome,
Italy.
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Swift mission measures distance to star explosions