April 6, 2005

In another first for the NASA-led space telescope mission calledSwift, five months into its mission it measured the distance to twogamma-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/OpticalTelescope (UVOT).

“Swift will detect more gamma-ray bursts than any satellite that hascome before it, and now will be able to pin down distances to many ofthese bursts too,” said Peter Roming, UVOT Lead Scientist at PennState. “These two aren’t distance record-breakers, but they’recertainly from far out there. The second of the two bursts was brightenough to be seen from Earth with a good backyard telescope.”

The Swift science team said these types of distance measurementswill become routine, allowing scientists to create a map to understandwhere, when and how these brilliant, fleeting bursts of light arecreated.

Gamma-ray bursts, the most powerfulexplosions known in the Universe, are thought to signal the birth ofblack holes; either from a massive star explosion or a merger ofsmaller black holes or neutron stars. Severalappear each day from Earth’s vantage point. They are difficult todetect and study because they occur randomly from any point in the skyand last only a few milliseconds to about a minute.

Swift, with three telescopes, is designed to detect bursts and turn onits own to focus its telescopes, within seconds, on the burstafterglow, which can linger for hours to weeks. The UVOT is a jointproduct of Penn State University and the Mullard Space Science Laboratory inEngland.

Swift detected the bursts on March 18 and 19, as indicted in theirnames: GRB 050318 and GRB 050319. The UVOT team estimated that theredshifts are 1.44 and 3.24, respectively, which corresponds todistances of about 9.2 billion and 11.6 billion light years. (Thesecond estimate reflects a more precise measurement made with theground-based Nordic Optical Telescope.)Distance measurements are attained through analysis of the burstafterglow.

Swift detected 24 bursts so far. GRB 050318 was the first burstwhere the UVOT detected an afterglow. The lack of afterglow detectionis interesting in its own right, Roming said, because it helpsscientists understand why some bursts create certain kinds ofafterglows, if any. For example, Swift’s X-RayTelescope (XRT) has detected afterglows from several bursts. The UVOTdetected afterglows in GRB 050318 and GRB 050319 in optical light, butnot significantly in ultraviolet.

“Every burst is a little different, and when we add them all up wewill begin to see the full picture,” said Keith Mason, the U.K. UVOTLead at University College London’s Mullard Space Science Laboratory.

Mason said UVOT distance measurements will become more precise inthe upcoming months as new instruments aboard Swift are employed.

Swift is a medium-class explorer mission managed by NASA Goddard SpaceFlight Center in Greenbelt, Maryland. Swift is a NASA mission withparticipation of the Italian Space Agency and the Particle Physics andAstronomy Research Council in the United Kingdom. It was built incollaboration with national laboratories, universities andinternational partners, including Penn State; Los Alamos NationalLaboratory in New Mexico; Sonoma State University in California; theUniversity of Leicester in Leicester, England; the Mullard SpaceScience Laboratory in Dorking, England; the Brera Observatory of theUniversity of Milan in Italy; and the ASI Science Data Center in Rome,Italy.