Swift Discovers 500th Burst
In 2004, NASA launched the Swift satellite to study explosive, high-energy events in the universe. Five years later, the spacecraft has recorded its 500th burst. This satellite was launched to study these strong, distant explosions, some of which are thought to occur when two neutron stars in a binary system merge, sending out a pulse of gravitational waves and what’s called a short gamma-ray burst.
Swift’s job is to focus on a burst and report its position so that other observatories can immediately start to study the phenomenon. As soon as it alerts observers, the satellite then focuses on the same explosion with an array of x-ray and ultraviolet/optical-sensitive telescopes. The resulting data are giving astronomers a much better sense of where these outbursts are occurring and a clearer look at the characteristics of each explosion (that is, the light-curves they exhibit).
Swift also studies other explosive events in the universe, such as exploding stars (supernovae, for example), outbursts from the regions near black holes, and high-energy surges from neutron stars. It is also doing a long-term survey of the entire sky in x-ray wavelengths.
Gamma-ray bursters are extremely fascinating to astronomers. This is because gamma-rays themselves are signals from the highest-energy types of events in the cosmos. A gamma-ray burster is a sign that something extremely energetic has occurred. What could it be? The answer to that question kept astronomers busy for years, coming up with models to explain just what kind of event could trigger such an energetic explosion. Some key breakthroughs came in 1997 when an Italian-Dutch satellite called Beppo-SAX provided very precise locations for some gamma-ray bursters. From that data, astronomers could zero in on the sources and spend time figuring out what the sources of the burst were. It was a cosmic detective story that Swift is continuing to follow up on. For more information on the 500th burst, check out the NASA press release.
In addition, I’m working on a special June 2010 segment of The Astronomer’s Universe about gamma-ray bursters, so stay tuned for more on these bright, formerly mysterious explosions that seem to come at us from every direction of the cosmos!
In a paper to be published in the Astrophysical Journal, available as a pre-print online now here an international team of astronomers including scientists associated with the NASA Swift Mission, examine the nature of the so-called dark gamma ray bursts (GRB). Most GRBs discovered by the Swift spacecraft have an associated optical afterglow. There is an elaborate network of telescopes set to lock in on any of the GRBs detected by the Swift spacecraft to catch these afterglows. However, some GRBs have been detected but they have not had an associated optical afterglow noted, but have had x-ray radiation detected. These authors conclude that “the previously suggested correlation between the optical darkness and the X-ray/gamma-ray brightness is merely an observational selection effect.” They propose a new classification method for categorizing these dark GRBs.
One of the major questions that remain for the gamma-ray observers, especially those associated with the NASA SWIFT spacecraft, is the nature of the so-called dark gamma-ray bursts (GRB). Usually, after the SWIFT spacecraft detects a GRB, optical telescopes that are part of a network of telescopes supporting the SWIFT mission, take a look in the direction of the GRB and find what is called an optical afterglow. In a number of cases, no optical afterglow is found, and these are the so-called “dark” GRBs. In this paper submitted to the Astrophysical Journal, an international team of astronomers present their searches for the host galaxies of these dark GRBs. The authors conclude that “the host galaxies of dark GRBs seem to have normal optical colors.” So what may be causing this “dark” phenomenon? The problem appears to be dust, and the authors present evidence that “the source of obscuring dust is local to the vicinity of the GRB.” However, in the end, the authors conclude that “the location and nature of this high-redshift dust remains unknown.” Read more about the search for the nature of dark GRBs online now here.
On 23 April 2009, NASA announced that its SWIFT satellite, containing a gamma-ray telescope, had detected the most distant object in the observable universe. It was called GRB 090423. You can read about this discovery online here. Today, the European Southern Observatory (ESO) announced that it has confirmed that GRB 090423, the gamma-ray burst detected last week, is indeed associated with an object whose redshift is about 8.2. That is, this gamma-ray burst actually occurred about 13 billion years ago, just a few hundred million years after the big bang origin of the universe itself. Read more about the ESO Very Large Telescope and GRB 090423 online now here.
NASA announced yesterday that it will keep a vigilant eye on a celestial object known as a soft gamma-ray repeater with two spacecraft. The object is SGR J1550-5418 and it lies in the southern hemisphere’s constellation called Norma. Due to its unusual nature (there are only 6 known SGRs), NASA will monitor this object with both its Fermi and Swift spacecraft. SGR J1550-5418 is also one of the class of objects referred to as a magnetar. Magnetars are neutron stars, whose magnetic fields are so powerful that they are sources of unusual gamma-ray emissions and/or x-ray emissions. Learn more about the vigilant monitoring of SGR J1550-5418 online at http://science.nasa.gov/headlines/y2009/10feb_sgr.htm
An international team of astronomers involved with the Swift satellite program released today a paper online at http://xxx.lanl.gov/PS_cache/arxiv/pdf/0812/0812.3662v1.pdf Within this paper the results of the X-ray telescope are summarized for all of the observed gamma-ray bursts (GRB) that the satellite has observed up to the writing of the paper, which will appear in the Monthly Notices of the Royal Astronomical Society. The Swift X-ray Telescope data are available online at http://www.swift.ac.uk/xrt_products/ NASA maintains a website explaining the data and how it’s archived at http://heasarc.gsfc.nasa.gov/docs/swift/archive/archiveguide1/node1.html Fully 24% of the GRBs observed by the SWIFT satellite are officially called “oddballs.” The official Swift Gamma-Ray Burst Mission webpage is located at http://heasarc.gsfc.nasa.gov/docs/swift/swiftsc.html
Yesterday, astronomers affiliated with the SWIFT satellite mission announced their analysis of an event noted by the SWIFT satellite on 13 September 2008, called GRB 080913. The origin of the gamma-ray burst detected by the satellite was determined to have a red-shift of about 6.7. That means that the object causing the gamma-ray burst was at a distance over 12 billion light years. That’s just a few billion years after the big bang origin of the universe. Take a look at the paper online at http://xxx.lanl.gov/PS_cache/arxiv/pdf/0812/0812.2470v1.pdf If you just read the introduction to the paper, you will see what it takes, i.e. many persons efforts, to get to the point of converting the data to intelligent information, you may better understand why there are often so many authors to papers like this.