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Record-Breaking X-ray Blast Briefly Blinds Space Observatory

14 Jul 2010, 15:07 UTC
Record-Breaking X-ray Blast Briefly Blinds Space Observatory NASA/Swift/Stefan Immler

A blast of the brightest X-rays ever detected from beyond our Milky Way galaxy's neighborhood temporarily blinded the X-ray eye on NASA's Swift space observatory earlier this summer, astronomers now report. The X-rays traveled through space for 5-billion years before slamming into and overwhelming Swift's X-ray Telescope on 21 June.

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.  (The image is 5 arcminutes
across.)

Credit:  NASA/Swift/Stefan Immler

A blast of the brightest X-rays ever detected from beyond our Milky
Way galaxy's neighborhood temporarily blinded the X-ray eye on NASA's
Swift space observatory earlier this summer, astronomers now report.
The X-rays traveled 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, 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 (XRT).

Although the Swift satellite was designed specifically to study
gamma-ray bursts, 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 Center.  He said the burst, named GRB
100621A, is the brightest X-ray source that Swift has detected since
the observatory began X-ray observation in early 2005.  "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.

"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, which is more that
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.

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.

The Swift scientists were able to estimate the overall brightness of
GRB 100621A by sampling the photons at some distance from its
overexposed center -- a standard correction technique.  Scientists
who study the Sun use a similar approach to observe the Sun's corona
by blocking out its much-brighter center.  "With this burst, we had
to sample the photons twice as far from the center as we ever had to
go before," Burrows said.  "The correction factor for the X-rays from
GRB 100621A was 168 times larger than for a typical gamma-ray burst
and 5 times larger than for the brightest burst we previously had
seen.  We never thought we'd see anything this bright."

Automated analysis of the Swift XRT data is performed at the
University of Leicester in the United Kingdom, which has been
studying X-rays from outer space for the past half century.  Evans
was the first to see the processed data from the burst's initial
blast.  "When I first saw the strange data from this burst, I knew
that I had discovered something extraordinary," he said.  "It was an
indescribable feeling when I realized, at that moment, that I was the
only person in the whole universe who knew that this extraordinary
event had occurred.  Now, after our analysis of the data, we know
that this burst is one for the record books."

Other members of the research team include Tilan Ukwatta at NASA
Goddard Space Flight Center and Valerio D'Elia and Giulia Stratta at
the ASI Science Data Center in Italy.
[ Barbara K. Kennedy ]

SCIENCE CONTACTS:
David Burrows, lead scientist for Swift's X-ray Telescope and a
senior scientist and professor of astronomy and astrophysics at Penn
State: 814 865-7707, burrows@astro.psu.eduNeil Gehrels, Swift principal investigator at NASA's Goddard Space
Flight Center: 301-286-6546, gehrels@gsfc.nasa.gov

P.I.O. CONTACTS:
Barbara K. Kennedy (Penn State PIO):  814-863-4682, science@psu.eduLynn Cominsky (Swift PIO): 707-664-2655, lynnc@universe.sonoma.edu

MORE ABOUT GRB 100621A
NASA's "Geeked on Goddard" blog has a related story about the GRB
100621A burst at
http://geeked.gsfc.nasa.gov/?p=1417

ABOUT THE SWIFT OBSERVATORY
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.  Its science and science and flight
operations are controlled by Penn State from the Mission Operations
Center in State College, Pennsylvania.  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, Maryland, and Los Alamos National Laboratory in New Mexico
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 the United Kingdom
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.

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