Swift Sees an Unusual Gamma Ray Burst

The strange cosmic explosion that occured on February 18th. Image credit: SDSS/Swift Click to enlarge
The Swift satellite, whose mission control center is in State College, has detected a cosmic explosion that has sent scientists around the world scrambling to telescopes to document this startling event. Gamma-ray radiation from the source, detected on 18 February and lasting about half an hour, appears to be a precursor to a supernova, which is the death throes of a star much more massive than the Sun. “The observations indicate that this is an incredibly rare glimpse of an initial gamma-ray burst at the beginning of a supernova,” said Peter Brown, a Penn State graduate student and a member of the Swift science team.

Astronomers are using Swift, whose science and flight operations are controlled by Penn State from the Mission Operations Center in State College, to continue to observe the event. Scores of satellites and ground-based telescopes also are now trained on the sight, watching and waiting. Amateur astronomers in the northern hemisphere with a good telescope in dark skies also can view the source.

The explosion has the trappings of a gamma-ray burst, the most distant and powerful type of explosion known. This event, however, was about 25 times closer and 100 times longer than the typical gamma-ray burst. “This burst is totally new and unexpected,” said Neil Gehrels, Swift principal investigator at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “This is the type of unscripted event in our nearby universe that we hoped Swift could catch.”

The explosion, called GRB 060218 after the date it was discovered, originated in a star-forming galaxy about 440 million light-years away toward the constellation Aries. This is the second-closest gamma-ray burst ever detected, if indeed it is a true burst.

Derek Fox, assistant professor of astronomy and astrophysics at Penn State, who is leading the monitoring effort of GRB 060218 on the Hobby-Eberly Telescope, commented, “This is the burst we’ve been waiting eight years for,” referring to the closest-ever gamma-ray burst, which was detected in 1998. “The special capabilities of Swift, which was not operating in 1998, combined with the intense campaign of ground-based telescopes, should help unravel this mystery,” said Fox.

“There are still many unknowns,” said Penn State Professor of Astronomy and Astrophysics John Nousek, the Swift mission operations director at Penn State University in University Park, Pennsylvania. The burst of gamma rays lasted for nearly 2,000 seconds; in contrast, most such bursts last a few milliseconds to tens of seconds. The explosion also was surprisingly dim. “This could be a new kind of burst, or we might be seeing a gamma-ray burst from an entirely different angle,” he said. The standard theory for gamma-ray bursts is that the high-energy light is beamed in our direction. “This off-angle glance–a profile view, perhaps–has given us an entirely new approach to studying star explosions. Had this burst been farther away, we would have missed it,” Nousek explained.

Because the burst was so long, Swift was able to observe the bulk of the explosion with all three of its instruments: the Burst Alert Telescope, which detected the burst; and the X-ray Telescope, and Ultraviolet/Optical Telescope, which provide high-resolution imagery and spectra across a broad range of wavelengths. Penn State lead the development of the X-ray and Ultraviolet/Optical Telescopes.

Scientists will attempt observations with the Hubble Space Telescope and the Chandra X-ray Observatory. Amateur astronomers in dark skies might be able to see the explosion with a 16-inch telescope as it hits 16th-magnitude brightness.

Swift is a NASA mission in partnership with the Italian Space Agency and the Particle Physics and Astronomy Research Council in the United Kingdom; it is managed by NASA Goddard, and Penn State controls its science and flight operations from the Mission Operations Center in University Park, Pennsylvania.

PSU News Release