Gamma Ray Bursts | Universe Today

This image shows the afterglow of GRB 090423 (red source in the centre) and was created from images taken in the z, Y and J filters at Gemini-South and VLT (credit: A. J. Levan).

On April 23, 2009 the Swift satellite detected a gamma ray burst and as we reported back in April, scientists soon realized that it was more than 13 billion light-years from Earth. GRB 090423 occurred 630 million years after the Big Bang, when the Universe was only four percent of its current age of 13.7 billion years. Now, continued observations of the GRB by astronomers around the world have yielded more information about this dramatic and ancient event: the GRB didn't come from a monster star, but it produced a fairly sizable explosion.
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While the Fermi Space Telescope has mapped the gamma ray sky with unprecedented resolution and sensitivity, it now has been able to take a measurement that has provided rare experimental evidence about the very structure of space and time, unified as space-time. Einstein's theory of relativity states that all electromagnetic radiation travels through a vacuum at the same speed. Fermi detected two gamma ray photons which varied widely in energy; yet even after traveling 7 billion years, the two different photons arrived almost simultaneously.
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Black holes get a bad rap. Most people are afraid of them, and some think black holes might even destroy Earth. Now, scientists from the University of Leeds are blaming black holes for causing the most energetic and deadly outbursts in the universe: gamma ray bursts.
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Thanks to the Swift satellite and several ground based optical telescopes, astronomers are learning more about so-called “dark” gamma-ray bursts, which are bright in gamma- and X-ray emissions but with little or no visible light. These dark bursts are also providing astronomers with insights on finding areas of star formation that are hidden by dust. “Our study provides compelling evidence that a large fraction of star formation in the universe is hidden by dust in galaxies that do not appear otherwise dusty,” said Joshua Bloom, associate professor of astronomy at UC Berkeley and senior author of the study, who presented his findings at the American Astronomical Society meeting in California.
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A really, really long time ago in a galaxy far away, a massive star exploded. On April 23, 2009, the Swift satellite detected that explosion. This spectacular gamma ray burst was seen 13 billion light years away, with a redshift of 8.2, the highest ever measured. As we hinted yesterday, this object is now the most distant known object, and the burst occurred when the Universe was only 630 million years old, a mere one-twentieth of its current age. This event, called GRB 090423, can tell us much about the early Universe. "We completely smashed the record with this one," said Edo Berger, a professor at Harvard University and a member of the team that first measured the burst’s origin. "This demonstrates for the first time that massive stars existed in the early Universe."
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According to the Sky and Telescope blog, NASA's Swift satellite captured a faint gamma-ray burst (GRB) last Thursday which has smashed the record for the earliest, most distant known object in the universe. Various ground-based telescopes following up on Swift's initial detection of the GRB have measured redshifts of the object, varying from 7.6 to 8.2. Whatever the final determination is of how much this GRB's afterglow has been redshifted by the expansion of the Universe, it will set a record. In September 2008, Swift captured GRB 080913, the most distant gamma-ray burst ever detected, with a redshift of 6.7. Astronomers using the Very Large Telescope in Chile have determined that this current GRB (090423) went off about 600 million years after the Big Bang.
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Compact, ultrabright jets at supermassive black holes in active galaxies were already known to pack an impressive punch in radio waves.  And now, an international team of scientists says they're kicking out high-energy gamma rays too.

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This could be titled "87 Days of Fermi," or "Blazing Galaxies:" This movie is made from the first 87 days of data gathered by Fermi's Large Area Telescope (LAT), showing all the gamma ray sources detected so far, with active galaxies called blazars flaring and fading in this all-sky movie. “The movie shows counts of gamma rays seen by Fermi’s LAT, and each frame shows the gamma rays collected in one day,” said Elizabeth Hays, an astrophysicist on the Fermi team. Visible are rapid and dramatic flashes, which underscores one of the most valuable things Fermi does. “We watch the sky all the time and alert other telescopes, in space and on the ground, when something interesting is going on,” Hays said.
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This artist's impression illustrates how a gamma-ray burst can flare dramatically over a short time period. Credits: ESA (Illustration by AOES Medialab)

The European Space Agency's Integral spacecraft has captured one of the brightest gamma-ray bursts ever seen. In looking at the data, astronomers have been able to investigate the initial phases of this giant stellar explosion, which ejected matter at velocities close to the speed of light. Astronomers also believe the explosion lifted a piece of the central engine’s magnetic field into space. The GRB reached Earth on December 19, 2004, and since then the Integral team has been meticulously dissecting the data.
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Astronomers have now been able to see the very early stages of a gamma ray burst, thanks to the Swift satellite. The Ultraviolet/Optical Telescope (UVOT) on board the satellite provided an ultraviolet spectrum of a GRB just 251 seconds after its onset – the earliest ever captured. Further use of the instrument in this way will also allow distance and brightness of GRBs to be calculated within a few hundred seconds of their initial outburst, as well as gather new information about the causes of bursts and the galaxies they originate from.

“The UVOT’s wavelength range, coupled with the fact that Swift is a space observatory with a speedy response rate, unconstrained by time of day or weather, has allowed us to collect this early ultraviolet spectrum,” said Martin Still from the Mullard Space Science Laboratory (MSSL) at UCL.
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GRB 080916C's X-ray afterglow appears orange and yellow in this view that merges images from Swift's UltraViolet/Optical and X-ray telescopes. Credit: NASA/Swift/Stefan Immler

The collapse of very massive stars can produce violent explosions, accompanied by strong bursts of gamma-ray light, which are some of the brightest events in the universe. Typical gamma-ray bursts emit photons with energies between 10 kiloelectron volts and about 1 megaelectron volt. Photons with energies above megaelectron volts have been seen in some very rare occasions but the distances to their sources were not known. An international research consortium is reporting in this week's issue of the journal Science Express that the Fermi Gamma-Ray Space Telescope has detected photons with energies between 8 kiloelectron volts and 13 gigaelectron volts arriving from the gamma-ray burst 080916C.

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NASA's Swift satellite and Fermi Gamma-ray Space Telescope have keyed in on a rowdy stellar remnant 30,000 light-years away. The object, already known as a source of pulsing radio and X-ray signals, lies in the southern constellation Norma. It kicked out some moderate eruptions in October, but then it settled down again. Late last month, it roared to life.

"At times, this remarkable object has erupted with more than a hundred flares in as little as 20 minutes," said Loredana Vetere, who is coordinating the Swift observations at Pennsylvania State University. "The most intense flares emitted more total energy than the sun does in 20 years."

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From 1991 to 2000, the Compton Gamma Ray Observatory dominated the search for the largest explosions ever observed in the cosmos: gamma-ray bursts (or GRBs). Unfortunately after nearly a decade of highly successful observations, June 4th 2000, NASA made the unpopular decision to de-orbit the observatory in response to a mechanical failure on the spacecraft (despite protests by some scientists, pointing out that the observatory could have continued operations).

To one scientist, Jim Ryan, the demise of the project he had tirelessly worked on since 1984 was a hard pill to swallow. However, in a surprise turn of events, the US Department of Energy tracked down Ryan and asked whether his research could be applied a little closer to home. In a flash of inspiration, the scientist realised spare parts left over from the Compton Gamma Ray Observatory could be used to pinpoint emissions from a potential "dirty bomb", possibly providing security services with an early warning capability against a radioactive terrorist attack…
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NASA's Swift satellite captured the most distant gamma-ray burst ever detected. The blast came from an exploding star 12.8 billion light-years away, near the edge of the visible universe. Swift saw the explosion on September 13 at 1:47 am EDT. But because light moves at finite speed, and looking farther into the universe means looking back in time, this means the burst occurred less than 825 million years after the universe began, or when the universe was less than one-seventh its present age. This star was probably from the earliest generations of stars ever formed. "This is the most amazing burst Swift has seen," said the mission's lead scientist Neil Gehrels at NASA's Goddard Space Flight Center.
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Artists depiction of GRB 080319B Credit: NASA/Swift/Mary Pat Hrybyk-Keith and John Jones

On March 19, 2008 at 2:13 am EDT, NASA's Swift satellite detected an explosion from the constellation Bootes, and sent an alert to ground-based telescopes. At the same moment, the Russian KONUS instrument on NASA's Wind satellite and a robotic wide-field optical camera called "Pi of the Sky" in Chile captured the first visible light from this incredibly bright and powerful gamma ray burst. Within the next 15 seconds, the burst brightened enough to be visible in a dark sky to human eyes. For a few moments, the GRB had a million times the luminosity of the entire Milky Way Galaxy. It briefly crested at a magnitude of 5.3 on the astronomical brightness scale. Incredibly, the dying star was 7.5 billion light-years away. Astronomers say the reason this gamma ray burst was so bright was that it was aimed almost directly at Earth.
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