Satellite has found 500 of the biggest explosions in the universe

University Park, Pa. -- NASA's Swift satellite, whose science and flight operations are controlled from Penn State's Mission Operations Center in State College, Pa., has detected its 500th gamma-ray burst -- a type of explosion that is the biggest and most mysterious in the cosmos. Swift's X-ray telescope and ultraviolet/optical telescope were developed and built by international teams led by Penn State.

"Over its five years in orbit and its 500 gamma-ray-bursts detections, Swift has fulfilled every significant promise of its mission and, in addition, has brought a wealth of surprises," said Derek Fox, assistant professor of astronomy at Penn State and astrophysics and a Swift team member. The spacecraft's "burst-o-meter" cataloged its 500th gamma-ray burst on April 13.

"Swift has been remarkably successful, far exceeding our expectations for a mission that was originally going to last only two years," said David Burrows, Penn State senior scientist and professor of astronomy and astrophysics, the lead scientist for Swift's X-ray telescope, and one of the leaders of the Swift mission since its beginning.

The Swift satellite has given astronomers more discoveries than they could have hoped for, ranging from a supernova relatively near to Earth, in astronomical terms, to a blast so far away that it happened when our universe was only 5 percent of its present age.

"By catching 500 gamma-ray bursts 'on the fly' and studying them in unprecedented detail, Swift has given us a much deeper understanding of these elusive explosions and their role in shaping our universe," Burrows said. Among other things, gamma-ray bursts signal the death of massive stars and the birth of black holes.

Burst number 500, officially known as GRB 100413B, exploded in constellation Cassiopeia as a long burst, a type usually associated with the death of a massive star. It was recorded by the spacecraft's Burst Alert Telescope (BAT), whose data later were analyzed by David Palmer, an astrophysicist at Los Alamos National Laboratory in New Mexico.

"The BAT team regularly digs through the data once it comes to the ground and finds weak bursts like this one that take a bit of special care," said Judith Racusin at NASA's Goddard Space Flight Center, who coordinated burst observations that day. Racusin earned her doctoral degree in astronomy and astrophysics at Penn State.

Some of the other Penn State researchers who contributed to the milestone detection with Swift of its 500th gamma-ray burst include Peter Meszaros, the holder of the Eberly Family Chair in Astronomy and Astrophysics at Penn State, a Penn State professor of physics and the leader of the Swift Theory Team; John Nousek, Penn State professor of astronomy and astrophysics and Swift's leader for mission operations; and Peter Roming, leader of the Swift UV/Optical Telescope.

Gamma rays are the highest-energy form of light, and the brief but brilliant blasts result from a colossal energy release. Gamma-ray bursts (GRBs) were discovered in 1967 by unclassified military satellites designed to look for clandestine nuclear tests. The first observations required extensive analysis to be sure that the bursts were truly originating beyond the solar system, and they weren't published until 1973. Over the following years, astronomers learned that sufficiently sensitive instruments could detect about two bursts per day, on average, somewhere in the sky. Of those twice-daily GRBs, Swift's Burst Alert Telescope snares about one in eight for detailed study.

Astronomers scramble to detect afterglow from new GRBs as fast as they can. Afterglows in visible light provide information that confirms the burst's distances from Earth, and astronomers now regularly study afterglows across the entire electromagnetic spectrum. Most of the time, the hard task of measuring burst distances falls to ground-based observatories, which can target a burst's location with telescopes far larger than the Ultraviolet/Optical Telescope aboard Swift.

"Getting on the afterglows quickly with large ground-based telescopes remains a key element in understanding GRBs," said Fox, whose research focuses on follow-up observations. "It's this synergy between Swift and ground observatories that has really moved the ball forward, especially for short bursts and bursts that are very far away."

Swift has detected 75 percent of all the GRBs whose distances have been measured.

"Swift has seen GRBs as close as about 100 million light-years and as far away as 13 billion light-years," said Gehrels.

Put another way, Swift has detected gamma-ray bursts over a span of time equivalent to about 95 percent of the universe's age.

For more information, contact Fox at 814-863-4989 or [email protected]; Burrows at 814-863-2466, [email protected] or [email protected]; Gehrels at 301-286-6546 or [email protected]; Penn State PIO Barbara K. Kennedy at 814-863-4682 or [email protected]; or Lynn Cominsky, Swift PIO, at 707-664-2655 or [email protected].

More About Swift
Swift was launched in November 2004 and was fully operational by January 2005. Swift carries three main instruments: the burst alert telescope, the X-ray telescope, and the ultraviolet/optical telescope. Swift's gamma-ray detector, the burst alert telescope, provides the rapid initial location and was built primarily by the NASA Goddard Space Flight Center in Greenbelt and Los Alamos National Laboratory and constructed at GSFC. Swift's X-ray telescope and UV/optical telescope were developed and built by international teams led by Penn State and drew heavily on each institution's experience with previous space missions. The X-ray telescope resulted from Penn State's collaboration with the University of Leicester in England and the Brera Astronomical Observatory in Italy. The ultraviolet/optical telescope resulted from Penn State's collaboration with the Mullard Space Science Laboratory of the University College-London. These three telescopes give Swift the ability to do almost immediate follow-up observations of most gamma-ray bursts because Swift can rotate so quickly to point toward the source of the gamma-ray signal. The spacecraft was built by General Dynamics.