STFC: Cosmic explosion may be 'most distant' ever seen

[bystander]

Cosmic explosion may be 'most distant' ever seen
Science & Technology Facilities Council | 2011 May 25

An international team, led by astronomers in the UK and US, has announced the discovery of what appears to be the most distant explosion, and possibly the most distant object, ever seen in the Universe.

The exploding star, known as a Gamma-ray Burst (GRB) was briefly as bright as several thousand galaxies (more than a million million times the brightness of the sun), which allowed it to be detected at an estimated distance of 13.14 billion light years (putting it 96% of the way to the edge of our observable Universe).

The research is presented in a paper by an international team of astronomers, with major contributions from UK scientists at the Universities of Warwick and Leicester, who receive grants from STFC. The research uses the Swift satellite, the Gemini North Observatory and the Hubble Space Telescope and is accepted for publication in the Astrophysical Journal.

Massive explosion helps Warwick researcher spot Universe’s most distant object
University of Warwick | 2011 May 25

An international team of UK and US astronomers have spotted the most distant explosion, and possibly the most distant object, ever seen in the Universe.

University of Warwick astronomer Dr Andrew Levan was one of the first members of that team to spot the exploding star, known as a Gamma-ray Burst (GRB), which was briefly as bright as several thousand galaxies (more than a million million times the brightness of the sun). This very bright explosion allowed it to be detected at an extreme estimated distance of 13.14 billion light years - putting it 96% of the way to the edge of Universe and making it most distant object ever seen.

The gamma-ray burst was first detected by NASA's Swift satellite in April 2009. The research team spent two years carrying out a careful examination of their data to see if the burst really was a record-breaker. “The more we examined this burst, the better it looked.” says Dr Andrew Levan.

Thanks to their extreme brightness, gamma-ray bursts can be detected by Swift and other satellite observatories even when they occur at distances of billions of light years. While the bursts themselves last for minutes at most, their fading "afterglow" light remains observable with large telescopes for days or even weeks. By performing a sophisticated analysis of this light, the research team were able to show that the burst most likely has a redshift (the means astronomers use to measure distance) of approximately 9.4. While there is some uncertainty due to the faintness of the source, this is significantly greater than the previous record holding GRB, which had a redshift of 8.2.

Dr Andrew Levan of the University of Warwick, one of the first people to observe the explosion and the second author of the paper, said: "The race to find distant objects stems from the desire to find and study the first stars and galaxies that formed in the Universe, in the first few hundred million years after the Big Bang.”

“By looking very far away, because the light takes so long on its journey to reach the Earth, astronomers are effectively able to look back in time to this early era. Unfortunately, the immense distances involved make this very challenging. There are different ways of finding such objects, looking at distant galaxies being the most obvious, but because galaxies are faint it is very difficult. GRB afterglows are so much brighter”.

The researchers used the Swift satellite, the Gemini North Observatory and the Hubble Space Telescope.

"This GRB shows us that there is a lot of action going on in the Universe which we can't currently see," Said Professor Nial Tanvir, from the University of Leicester and the leader of the Hubble Space Telescope part of this research programme, "Our observations show us that even the Hubble Space Telescope is only seeing the tip of the iceberg in the distant Universe".

Swift is capable of finding some GRBs at distances corresponding to when the first stars are predicted in the Universe", said Prof Paul O'Brien a member of the Swift team at Leicester.

Cosmic Explosion is New Candidate for Most Distant Object in the Universe
Penn State University | 2011 May 25

A gamma-ray burst detected by NASA's Swift satellite in April 2009 has been newly unveiled as a candidate for the most distant object in the universe. At an estimated distance of 13.14 billion light years, the burst lies far beyond any known quasar and could be more distant than any previously known galaxy or gamma-ray burst. Multiple lines of evidence in favor of a record-breaking distance for this burst, known as GRB 090429B for the 29 April 2009 date when it was discovered, are presented in a paper by an international team of astronomers led by former Penn State University graduate student Antonino Cucchiara, now at the University of California, Berkeley. The paper has been accepted for publication in the Astrophysical Journal.

The gigantic burst of gamma rays erupted from an exploding star when the universe was less than 4% of its present age, just 520 million years old, and less than 10% of its present size. "The galaxy hosting the progenitor star of GRB 090429B was truly one of the first galaxies in the universe," said Derek Fox, associate professor of astronomy and astrophysics at Penn State and a co-author of the paper. "Beyond the possible cosmic distance record, GRB 090429B illustrates how gamma-ray bursts can be used to reveal the locations of massive stars in the early universe and to track the processes of early galaxy and star formation that eventually led to the galaxy-rich cosmos we see around us today."

Gamma-ray bursts, the brightest explosions known, occur somewhere within the observable universe at a rate of about two per day. Thanks to their extreme brightness, gamma-ray bursts can be detected by Swift and other satellite observatories even when they occur at distances of billions of light years. While the bursts themselves last for minutes at most, their fading "afterglow" light remains observable from premier astronomical facilities for days to weeks. Detailed studies of the afterglow during this time, when feasible, allow astronomers to measure the distance to the burst.

These afterglow measurements were used to determine a cosmic distance record in 2009 for an earlier gamma-ray burst, GRB 090423 at a distance of 13.04 billion light years from Earth, making it temporarily the "most distant object in the universe." This record was surpassed by galaxy discoveries in 2010 and 2011 that pushed the cosmic frontier out to 13.07 billion light years, and potentially even further. "Our extreme estimate of the distance to GRB 090429B makes this a sort of 'revenge of the bursts,'" said Cucchiara. "A gamma-ray burst is once more contending for the title of most distant object in the cosmos -- beyond the previously known most-distant quasars and galaxies."

Less than a week after the record-setting GRB 090423 made headlines around the world, this new burst, GRB 090429B, appeared in the sky with suspiciously similar properties. As with the previous burst, GRB 090429B was a short-lived event, lasting less than 10 seconds, and automated Swift observations showed it to have a relatively faint X-ray afterglow. Cucchiara, then a graduate student at Penn State, woke up in the early morning hours to direct observations at the Gemini North telescope on Mauna Kea, Hawaii, that he hoped would pin down the nature of this burst. Working with coauthors Andrew Levan of the University of Warwick, Nial Tanvir of the University of Leicester, and thesis supervisor Derek Fox of Penn State, Cucchiara found that, while the afterglow was visible in infrared observations, no optical light could be detected. This "drop out" behavior is a distinctive signature of the most-distant objects, and has been used for initial identification of all of the most-distant quasars, galaxies, and gamma-ray bursts.

Cucchiara requested an immediate spectrum of the GRB 090429B afterglow from the Gemini operators, which would have provided a definitive measurement of the distance to the burst. Unfortunately, just as the spectrum was about to be taken, clouds blew in over the summit of Mauna Kea and hid the afterglow from sight. By the next night, the afterglow was too faint to yield a useful spectrum, and over the following nights it faded from view completely. "It was frustrating to lose sight of this burst, but the hints we had were so exciting there was no chance of us letting it go," said Cucchiara, who presented an initial study of the burst as part of his doctoral thesis at Penn State.

Determined not to let GRB 090429B become "the burst that got away," the team spent two years carrying out a careful examination of their data to see if the burst is truly a candidate record-breaker, or might be a partially-obscured burst in a galaxy at a less dramatic distance. Importantly, this work has meant gathering new data -- deep observations with Gemini and the Hubble Space Telescope that would have revealed a galaxy at the burst position in any of the less-dramatic scenarios. This evidence, including the missing galaxy, indicates that the burst is extremely likely -- a 99.3-percent chance -- to be the most distant cosmic explosion, beyond the record set by GRB 090423. "Like the best politicians or talent-show contestants, the more we examined this burst, the better it looked," says Levan, the paper's second author.

Whether GRB 090429B is now the most distant object in the universe depends on several factors which are not precisely known. First, it must lie beyond the 13.07-billion-light-year distance to a galaxy reported in 2010 by a team of astronomers led by Matthew Lehnert at the Observatoire de Paris. This is very likely to be the case, at 98.9% probability, but is not certain. It also has to lie beyond the distance of a galaxy reported in 2011 by a team of astronomers led by Rychard Bouwens of U.C. Santa Cruz. This could be either easy or hard: The Bouwens team estimates that there is a 20% chance their galaxy is not a record breaker at all, but simply a faint galaxy at a relatively modest distance; on the other hand, if the Bouwens galaxy is a record-breaker, it is very distant indeed, from 13.11 to 13.28 billion light years away, and there is only a 4.8% chance that GRB 090429B is more distant than that. Overall, and treating these uncertainties as perfectly understood, there is a 23% chance that GRB 090429B is now the most distant known object in the Universe, the astronomers said.

With better luck, or more advanced facilities, it should be possible in the future to use the bright afterglows of bursts like GRB 090423 and GRB 090429B to explore the conditions of star and galaxy formation at these early cosmic epochs in detail. "Discovering extremely distant bursts is pretty fun," says Fox, "but we suspect there is a whole lot more information in the bursts, waiting for us, that we have yet to access."

Betting on the Most Distant Gamma Ray Burst Ever Seen
Gemini Observatory | 2011 May 25

Extreme Distance Determined with Gemini Observatory Images

[attachment=0]GRB090429B.jpg[/attachment]

In a game of cosmological one-upmanship, what is likely the most distant gamma ray burst (GRB) ever detected could be presenting humanity with a glimpse back to within about half a billion years of the Big Bang. "Like any finding of this sort there are uncertainties,” said the study's principal investigator Antonino Cucchiara. “However, if I were in Vegas, I would never bet against the odds that this is the most distant GRB ever seen and we estimate that there is even a 23% chance that it is the most distant object ever observed in the universe."

A unique set of images from the Gemini North telescope in Hawai‘i clearly reveals the infrared afterglow of this powerful burst. More importantly, the data allowed the researchers to estimate its distance with a relatively high degree of certainty, placing it near the edge of the observable universe.

The finding, announced today at the American Astronomical Society meeting in Boston Massachusetts, follows the evolution of a gamma ray burst (GRB 090429B) discovered by NASA's Swift satellite in April of 2009. GRBs like this one are a consequence of the deaths of massive stars, with an initial brief burst of high-energy emission gradually fading to an afterglow of light at other wavelengths. The subsequent afterglow was detected only at infrared wavelengths using the Gemini North telescope.

This result follows on the heels of other announcements by astronomers over the past few years that have extended the edge of the observable universe and pushed the depth of our vision deeper and deeper into the past by looking at both GRBs and galaxies.

Astronomers quantify large distances in terms of redshift, “z” where higher values of z indicate greater distance and greater lookback time into the early universe. The previous GRB record holder has an estimated redshift or z value of around 8.2, with GRB 090429B estimated at 9.4. Other galaxies at comparable or even larger redshifts may have already been detected, although some of their distance estimates are uncertain.

The research team, led by former Penn State University graduate student Antonino Cucchiara (now at the University of California at Berkeley), marshaled the extreme vision of Gemini and other large ground- and space-based telescopes to understand the object. According to Cucchiara, “Gemini was the right telescope, in the right place, at the right time. The data from Gemini was instrumental in allowing us to reach the conclusion that the object is likely the most distant GRB ever seen.” If the team is correct, this light embarked on its journey some 13.1 billion years ago or about 520 million years after the Big Bang – surprisingly close to the advent of the Big Bang 13.7 billion years ago. Additionally, this GRB appears to be normal, leading to the conclusion that it is not the consequence of the very first generation of stars formed in the universe. The implication is that the early, extremely young universe was already a busy star factory.

Reaching the conclusion that GRB 090429B is so distant was not easy and is one reason it has taken two years for this result to be announced. “Ideally we would have gathered a spectrum to measure the distance precisely, but we were foiled at the last minute when the weather took a turn for the worse on Mauna Kea. Since GRB afterglows fade so quickly, we never got a second chance,” said Derek Fox, Cucchiara’s advisor for his graduate research at Penn State University.

However, by using the existing data from Gemini and combining it in innovative ways with wider-field images from the United Kingdom Infrared Telescope (also on Hawaii’s Mauna Kea), the team was able to estimate the redshift of GRB 090429B with a high degree of confidence. “Also, the fact that we were never able to detect anything in the spot where we saw the afterglow in the Gemini data gave us the missing link in converging on this extremely high redshift estimate,” said Cucchiara. “We looked with Gemini, the Hubble Space Telescope and also with the Very Large Telescope in Chile and never saw anything once the afterglow faded. This means that this GRB's host galaxy is so distant that it couldn’t be seen with any existing telescopes. Because of this, and the information provided by the Swift satellite, our confidence is extremely high that this event happened very, very early in the history of our universe.”

A Photometric Redshift of z ~ 9.4 for GRB 090429B - A Cucchiara et al

• Astrophysical Journal 736(1) 7 (2011 July 20) DOI: 10.1088/0004-637X/736/1/7
  arXiv.org > astro-ph > arXiv:1105.4915 > 25 May 2011 (v1), 31 May 2011 (v3)

[bystander]

Swift Finds Most Distant Gamma-ray Burst Yet
NASA GSFC Swift | 2011 May 27

View of GRB 090429B from Swift's X-Ray Telescope less than 107 seconds after the gamma-ray trigger. [i](Credit: NASA/Swift/Stefan Immler)[/i]

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On April 29, 2009, a five-second-long burst of gamma rays from the constellation Canes Venatici triggered the Burst Alert Telescope on NASA's Swift satellite. As with most gamma-ray bursts, this one -- now designated GRB 090429B -- heralded the death of a star some 30 times the sun's mass and the likely birth of a new black hole.

"What's important about this event isn't so much the 'what' but the 'where,'" said Neil Gehrels, lead scientist for Swift at NASA's Goddard Space Flight Center in Greenbelt, Md. "GRB 090429B exploded at the cosmic frontier, among some of the earliest stars to form in our universe."

Because light moves at finite speed, looking farther into the universe means looking back in time. GRB 090429B gives astronomers a glimpse of the cosmos as it appeared some 520 million years after the universe began.

Now, after two years of painstaking analysis, astronomers studying the afterglow of the explosion say they're confident that the blast was the farthest explosion yet identified -- and at a distance of 13.14 billion light-years, a contender for the most distant object now known.

Swift's discoveries continue to push the cosmic frontier deeper back in time. A gamma-ray burst detected on Sept. 4, 2005, was shown to be 12.77 billion light-years away. Until the new study dethroned it, GRB 090423, which was detected just six days before the current record-holder, reigned with a distance of about 13.04 billion light-years.

Gamma-ray bursts are the universe's most luminous explosions, emitting more energy in a few seconds than our sun will during its energy-producing lifetime. Most occur when massive stars run out of nuclear fuel. When such a star runs out of fuel, its core collapses and likely forms a black hole surrounded by a dense hot disk of gas. Somehow, the black hole diverts part of the infalling matter into a pair of high-energy particle jets that tear through the collapsing star.

The jets move so fast -- upwards of 99.9 percent the speed of light -- that collisions within them produce gamma rays. When the jets breach the star's surface, a gamma-ray burst is born. The jet continues on, later striking gas beyond the star to produce afterglows.

"Catching these afterglows before they fade out is the key to determining distances for the bursts," Gehrels said. "Swift is designed to detect the bursts, rapidly locate them, and communicate the position to astronomers around the world." Once word gets out, the race is on to record as much information from the fading afterglow as possible.

In certain colors, the brightness of a distant object shows a characteristic drop caused by intervening gas clouds. The farther away the object is, the longer the wavelength where this sudden fade-out begins. Exploiting this effect gives astronomers a quick estimate of the blast's "redshift" -- a color shift toward the less energetic red end of the electromagnetic spectrum that indicates distance.

The Gemini-North Telescope in Hawaii captured optical and infrared images of GRB 090429B's quickly fading afterglow within about three hours of Swift's detection. “Gemini was the right telescope, in the right place, at the right time," said lead researcher Antonino Cucchiara at the University of California, Berkeley. "The data from Gemini was instrumental in allowing us to reach the conclusion that the object is likely the most distant GRB ever seen."

The team combined the Gemini images with wider-field images from the United Kingdom Infrared Telescope, which is also located on Mauna Kea in Hawaii, to narrow estimates of the object's redshift.

Announcing the finding at the American Astronomical Society meeting in Boston on Wednesday, May 25, the team reported a redshift of 9.4 for GRB 090429B. Other researchers have made claims for galaxies at comparable or even larger redshifts, with uncertain distance estimates, and the burst joins them as a candidate for the most distant object known.

Studies by NASA's Hubble Space Telescope and the Very Large Telescope in Chile were unable to locate any other object at the burst location once its afterglow had faded away, which means that the burst's host galaxy is so distant that it couldn’t be seen with the best existing telescopes. "Because of this, and the information provided by the Swift satellite, our confidence is extremely high that this event happened very, very early in the history of our universe,” Cucchiara said.

[bystander]

Possibly the Most Distant Object Known
Smithsonian Astrophysical Observatory
Weekly Science Update | 2011 Jul 15

GRB 090429B, arguably the most distant object known [i](Credit: Gemini Observatory/AURA/Andrew Levan (Univ of Warwick))[/i]

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The most distant objects in the universe are also the oldest -- or at least that is how they appear to us, because their light has had to travel for billions of years to get here. They are also extraordinarily faint since they are so far away, and only in the last decade have astronomers been able to stretch their vision using the newest telescopes and clever techniques. One such innovation occurred with the launch of the NASA Swift satellite in 2004; it searches for bursts of gamma-ray emission, called GRBs. These flashes, thought to result from the especially spectacular deaths of massive stars, are the brightest events in the cosmos during their brief (only seconds-long) existence. But because they are so bright, they can be seen even when they are very, very far away.

A large international team of astronomers including CfA astronomers Edo Berger, Alicia Soderberg, and Ryan Foley used the Swift satellite to spot a GRB that rapid, ground-based followup studies determined was possibly the most distant object known (but measurement uncertainties allow a few other candidates to compete for this title). The light from this object has been traveling towards us for about 13.2 billion years, or 96% of the age of the universe. Since the universe is not static but expanding, today this object is much farther away than 13.2 billion light-years - more like about thirty billion light-years.

The scientists were unable to detect any faint trace of the putative galaxy in which this massive star once lived, helping to confirm the great distance of this GRB. Other important details in their new paper confirm that the object is similar to more nearby GRBs, and consequently that - even at this early stage of cosmic life - at least some stars already resembled stars in our local universe.

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