Blast blinds telescope

Gamma-ray burst GRB100621A

The brightest gamma-ray burst ever seen in X-rays temporarily blinded Swift's X-ray Telescope on 21 June 2010. This image merges the X-rays (red to yellow) with the same view from Swift's Ultraviolet/Optical Telescope, which showed nothing extraordinary.

  • Blast of X-rays from stellar explosion
  • Temporarily overwhelmed NASA’s Swift space observatory
  • Largest X-ray blast ever seen by Swift

A blast of the brightest X-rays ever detected from beyond our Milky Way galaxy’s neighbourhood temporarily blinded the X-ray eye on NASA’s Swift space observatory last month.

The X-rays had travelled through space for 5 billion years before slamming into and overwhelming Swift’s X-ray Telescope on 21 June.

The blindingly bright blast came from a gamma-ray burst (GRB), a violent eruption of energy from the explosion of a massive star morphing into a new black hole.

“This gamma-ray burst is by far the brightest light source ever seen in X-ray wavelengths at cosmological distances,” said David Burrows, senior scientist and professor of astronomy and astrophysics at Penn State University and the lead scientist for Swift’s X-ray Telescope.

Although the Swift satellite was designed specifically to study GRBs, the instrument was not designed to handle an X-ray blast this bright.

“The intensity of these X-rays was unexpected and unprecedented,” said Neil Gehrels, Swift’s principal investigator at NASA’s Goddard Space Flight Centre. He said the burst, named GRB 100621A, is the brightest X-ray source that Swift has detected since the observatory began work in early 2005.

Artist's impression of the Swift space observatory

The Swift space observatory (artist's impression) can swivel quickly in space to catch the fast flashes of energy from gamma-ray bursts.

“Just when we were beginning to think that we had seen everything that gamma-ray bursts could throw at us, this burst came along to challenge our assumptions about how powerful their X-ray emissions can be,” Gehrels said.

Blast so strong, Swift’s software shut down

“The burst was so bright when it first erupted that our data-analysis software shut down,” said Phil Evans, a postdoctoral research assistant at the University of Leicester in the United Kingdom who wrote parts of Swift’s X-ray-analysis software.

“So many photons were bombarding the detector each second that it just couldn’t count them quickly enough. It was like trying to use a rain gauge and a bucket to measure the flow rate of a tsunami.”

The software soon resumed capturing the evolution of the burst over time, and Evans recovered the data that Swift had detected during the software’s brief shutdown. The scientists then were able to measure the blast’s X-ray brightness at 143,000 X-ray photons per second during its fleeting period of greatest brightness.

That’s more than 140 times brighter than the brightest continuous X-ray source in the sky—a neutron star that is more than 500,000 times closer to Earth than the gamma-ray burst, and that sends a ‘mere’ 10,000 photons per second streaming toward Swift’s telescopes.

Artist's impression of a gamma-ray burst

Artist's impression of a gamma-ray burst, thought to occur when a large star explodes and implodes to become a black hole.

Rapid response to energy bursts

Gamma-ray bursts typically begin with a bright flash of high-energy gamma-rays and X-rays, then fade away like a fireworks display, sometimes leaving behind a disappearing afterglow in less-energetic wavelengths, including optical and ultraviolet.

Surprisingly, although the energy from this burst was the brightest ever in X-rays, it was merely ordinary in optical and ultraviolet wavelengths.

“We never thought we’d see anything this bright,” Burrows said.

The Swift observatory 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. The Burst Alert Telescope provides rapid initial location data.

The 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.

Adapted from information issued by Penn State / Barbara K. Kennedy / NASA / Swift / Stefan Immler.

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