Gamma ray burst

[
GRB-990123 taken on January 23, 1999. The burst is seen as a bright dot denoted by a square on the left, with an enlarged cutout on the right. The object above it with the finger-like filaments is the originating galaxy. This galaxy seems to be distorted by a collision with another galaxy.]

Gamma-ray bursts (GRBs) are the most luminous electromagnetic events occurring in the universe since the Big Bang. They are flashes of gamma rays emanating from seemingly random places in deep space at random times. The duration of a gamma-ray burst is typically a few seconds, but can range from a few milliseconds to several minutes, and the initial burst is usually followed by a longer-lived "afterglow" emitting at longer wavelengths (X-ray, ultraviolet, optical, infrared, and radio). Gamma-ray bursts are detected by orbiting satellites about two to three times per week, but the number of GRBs that could be observed from Earth is about three times this and is currently limited by the efficiency of the instruments.

Most observed GRBs appear to be collimated emissions caused by the collapse of the core of a rapidly rotating, high-mass star into a black hole. A subclass of GRBs (the "short" bursts) appear to originate from a different process, the leading candidate being the collision of neutron stars orbiting in a binary system. All known GRBs originate from outside our own galaxy; though a related class of phenomena, SGR flares, are associated with Galactic magnetars. The sources of most GRBs are billions of light years away.

A nearby gamma ray burst could possibly cause mass extinctions on Earth.cite journal|doi= 10.1017/S1473550404001910|author=Melott, A.L., "et al."|year=2004|title=Did a gamma-ray burst initiate the late Ordovician mass extinction?|journal=International Journal of Astrobiology|volume=3|pages=55–61] Though the short duration of a gamma ray burst would limit the immediate damage to life, a nearby burst might alter atmospheric chemistry by reducing the ozone layer and generating acidic nitrogen oxides. These atmospheric changes could ultimately cause severe damage to the biosphere.

Discovery and history

Cosmic gamma-ray bursts were discovered in the late 1960s by the US Vela nuclear test detection satellites. The Velas were built to detect gamma-radiation pulses emitted by nuclear weapon tests in space. The United States suspected that the USSR might attempt to conduct secret nuclear tests after signing the Nuclear Test Ban Treaty in 1963. Any discoveries of weapon tests have never been publicly declared and details of the Vela Incident, an as-yet unidentified flash of light over the South Atlantic on September 22, 1979, remain classified.

In a classic example of scientific serendipity, the satellites detected flashes of radiation that looked nothing like a nuclear weapons signature, coming from seemingly random directions in deep space. These results were published in 1973, [cite journal|url=http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1973ApJ...182L..85K&db_key=AST&data_type=HTML&format=&high=4322390bbe18783|author=Klebesadel, R. "et al."|year=1973|title=Observations of Gamma-Ray Bursts of Cosmic Origin|journal=Astrophysical Journal|volume=182|pages=L85 | doi = 10.1086/181225 ] prompting the scientific study of GRBs.

The presence of GRBs was confirmed later by many space missions such as Apollo and the Soviet Venera probes. To explain these events, many speculative theories were advanced, most of which posited nearby galactic sources. Little progress was made, however until the 1991 launch of the Compton Gamma Ray Observatory and its Burst and Transient Source Explorer (BATSE) instrument, an extremely sensitive gamma-ray detector. This instrument provided crucial data indicating that GRBs are isotropic (not biased towards any particular direction in space, such as toward the galactic plane or the galactic center), [cite journal|doi=10.1038/355143a0|author=Meegan, C.A., "et al."|year=1992|title=Spatial distribution of gamma-ray bursts observed by BATSE|journal=Nature|volume=355|pages=143] and therefore ruling out nearly all galactic origins. BATSE data also showed that GRBs fall into two distinct categories: short-duration, hard-spectrum bursts ("short bursts"), and long-duration, soft-spectrum bursts ("long bursts"). [cite journal|url=http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993ApJ...413L.101K&db_key=AST&link_type=ABSTRACT&high=4322390bbe25658|author=Kouveliotou, C. "et al."|year=1993|title=Identification of two classes of gamma-ray bursts|journal= Astrophysical Journal|volume=413|pages=L101 | doi = 10.1086/186969 ] Short bursts are typically less than two seconds in duration and are dominated by higher-energy photons; long bursts are typically more than two seconds in duration and dominated by lower-energy photons. The separation is not absolute and the populations overlap observationally, but the distinction suggests two different classes of progenitors. However, some believe there is a third type of GRBs. [cite journal|doi=10.1086/306386|author=Mukherjee, S., "et al."|year=1998|title=Three Types of Gamma-Ray Bursts|journal=Astrophysical Journal|volume=508|pages=314] [cite journal|doi=10.1086/306416|author=Horvath, I.|year=1998|title=A Third Class of Gamma-Ray Bursts?|journal=Astrophysical Journal|volume=508|pages=757] [cite journal|doi=10.1086/344568|author=Hakkila, J., "et al."|year=2003|title=How Sample Completeness Affects Gamma-Ray Burst Classification|journal=Astrophysical Journal|volume=582|pages=320] [cite journal|doi=10.1051/0004-6361:20041129|author=Horvath, I., "et al."|year=2006|title=A new definition of the intermediate group of gamma-ray bursts|journal=Astronomy and Astrophysics|volume=447|pages=23] [cite journal|doi=10.1086/520317|author=Chattopadhyay, T., "et al."|year=2007|title=Statistical Evidence for Three Classes of Gamma-Ray Bursts|journal=Astrophysical Journal|volume=667|pages=1017]

For decades after the discovery of GRBs astronomers could not find any counterpart or host to them, such as a star or galaxy, owing to poor resolution of their detectors. The best hope seemed to lie in finding a fainter, fading, longer wavelength emission after the burst itself, the "afterglow" of a GRB, as predicted by most models. [cite journal|doi= 10.1146/annurev.aa.33.090195.002215|author=Fishman, C. J. and Meegan, C. A.|year=1995|title=Gamma-Ray Bursts|journal=Annual Review of Astronomy and Astrophysics|volume=33|pages=415–458] In 1997 the Italian/Dutch satellite BeppoSAX detected a gamma-ray burst (GRB 970228),GRBs are named after the date on which they are discovered: the last two digits being the year, followed by the two-digit month and two-digit day. If two or more GRBs occur on a given day, the name is appended with a letter 'A' for the first burst identified, 'B' for the second and so on.] and when the X-ray camera was pointed in direction from which the burst had originated it detected a fading X-ray emission. Ground-based telescopes later identified a fading optical counterpart as well. [cite journal|doi=10.1038/386686a0|author=van Paradijs, J., "et al."|year=1997|title=Transient optical emission from the error box of the gamma-ray burst of 28 February 1997|journal=Nature|volume=386|pages=686] The location of this event having been identified, once the GRB faded, deep imaging was able to identify a faint, very distant host galaxy in the GRB location, the first of many to come. Not all scientists believed in this association at first, and the exact redshift of this particular galaxy was not obtained until many years later. However, the next well-localized gamma-ray burst, GRB 970508, had a firm absorption redshift of 0.835 - a distance of 7 billion light years, and unambiguously far beyond our galaxy.] Within only a few weeks the long controversy about the distance scale ended: GRBs were extragalactic events originating inside faint galaxies at enormous distance. [For more on galaxies hosting GRBs, see the GHostS database http://www.grbhosts.org] By finally establishing the distance scale, characterizing the environments in which GRBs occur, and providing a new window on GRBs both observationally and theoretically, this discovery revolutionized the study of GRBs. [cite book|author=Frontera, F. and Piro, L.|year=1998|title=Proceedings of Gamma-Ray Bursts in the Afterglow Era|publisher=Astronomy and Astrophysics Supplement Series|url=http://www.edpsciences.org/articles/aas/abs/1999/15/contents/contents.html]

As of 2007, a similar revolution in GRB astronomy is in progress, largely as a result of successful launch of NASA's Swift satellite in November 2004, which combines a sensitive gamma-ray detector with the ability to slew on-board X-ray and optical telescopes towards the direction of a new burst in less than a minute. [cite journal|url=http://adsabs.harvard.edu/abs/2004ApJ...611.1005G|author=Gehrels, N., et al.|year=2004|title=The Swift Gamma-Ray Burst Mission|journal=The Astrophysical Journal|volume=611|pages=1005–1020 | doi = 10.1086/422091 ] Swift's discoveries include the first observations of short burst afterglows and vast amount of data on the behavior of GRB afterglows at early stages during their evolution, even before the GRB's gamma-ray emission has stopped. The mission has also discovered huge X-ray flares appearing within minutes to days after the end of the GRB.

On June 11, 2008 NASA's Gamma-ray Large Area Space Telescope (GLAST), later renamed the Fermi Gamma-ray Space Telescope was launched.

Distance scale and energetics

Galactic vs. extragalactic models

Prior to the launch of BATSE, the distance scale to GRBs was completely unknown. Theories for the location of these events ranged from the outer regions of our own solar system to the edges of the known universe. The discovery that bursts were isotropic—coming from completely random directions—narrowed down these possibilities greatly, and by the mid 1990s only two theories were considered generally viable: that GRBs originate from a very large, diffuse halo (or "corona") around our own galaxy, or that they originate from distant galaxies far beyond our local group.

Supporters of the galactic model pointed to the class of well-known objects known as soft gamma repeaters (SGRs), highly magnetized galactic neutron stars known to periodically erupt in bright flares at gamma-ray and other wavelengths, and stated that there may be an unobserved population of similar objects at greater distances, producing GRBs. [cite journal|url=http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1995PASP..107.1152|author=Lamb, D. Q.|year=1995|title=The Distance Scale to Gamma-Ray Bursts|journal=Publications of the Astronomical Society of the Pacific|volume=107|pages=1152 | doi = 10.1086/133673 ] Furthermore, the sheer brightness of a typical gamma-ray burst would impose enormous requirements on the energy released in such an event if it really occurred in a distant galaxy.

Supporters of the extragalactic model claimed that the galactic neutron-star hypothesis involved too many ad-hoc assumptions in order to reproduce the degree of isotropy reported by BATSE and that an extragalactic model was far more natural regardless of its problems. [cite journal|url=http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1995PASP..107.1167P|author=Paczynski, B.|year=1995|title=How Far Away Are Gamma-Ray Bursters?|journal=Publications of the Astronomical Society of the Pacific|volume=107|pages=1167 | doi = 10.1086/133674 ]

The discovery of afterglow emission associated with faraway galaxies definitively supported the extragalactic hypothesis. Not only are GRBs extragalactic events, but they are also observable to the limits of the visible universe; a typical GRB has a redshift of at least 1.0 (corresponding to a distance of 8 billion light-years), while the most distant known (GRB 080913) has a redshift of 6.7 (corresponding to a distance of 12.8 billion light years). GRB 080913's "lookback time" reveals thatthe burst occurred less than 825 million years after the universe began. The previous record holder was a burst with a redshift of 6.29, which placed it 70 million light-years closer than GRB 080913. [cite journal|url=http://gcn.gsfc.nasa.gov/gcn3/8225.gcn3|year=2008|title=GCN circular:GRB 080913: VLT/FORS spectrum] As observers are able to acquire spectra of only a fraction of bursts - usually the brightest ones - many GRBs may actually originate from even higher redshifts.

GRB Jets: collimated emission

Many GRBs have been observed to undergo a jet break in their light curve, during which the optical afterglow quickly changes from slowly fading to rapidly fading as the jet slows down. [cite journal|url=http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999ApJ...519L..17S&db_key=AST|author=Sari, R., Piran, T., Halpern, J. P.|year=1999|title=Jets in Gamma-Ray Bursts|journal=Astrophysical Journal|volume=519|pages=L17–L20|doi=10.1086/312109] Furthermore, features suggestive of significant asymmetry have been observed in at least one nearby type Ic supernova, which may have the same progenitor stars as GRBs and have been observed to accompany GRBs in some cases (see ""). The jet opening angle (degree of beaming), however, varies greatly, from 2 degrees to more than 20 degrees. There is some evidence which suggests that the jet angles and apparent energy released are correlated in such a way that the true energy release of a (long) GRB is approximately constant—about 10⁴⁴ J, or around 1/2000 of a solar mass. [cite journal|url=http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001ApJ...562L..55F&db_key=AST|author=Frail, D.A. "et al."|year=2001|title=Beaming in Gamma-Ray Bursts: Evidence for a Standard Energy Reservoir|journal=Astrophysical Journal|volume=562|pages=L55–L58 | doi = 10.1086/338119 ] This is comparable to the energy released in a bright type Ib/c supernova (sometimes termed a "hypernova"). Bright hypernovae do in fact appear to accompany some GRBs. [cite journal|url=http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1998Natur.395..670G&db_key=AST|author=Galama, T. J. "et al."|year=1998|title=An unusual supernova in the error box of the gamma-ray burst of 25 April 1998|journal=Nature|volume=395|pages=670–672 | doi = 10.1038/27150 ]

The fact that GRBs are jetted also suggests that there are far more events occurring in the Universe than those actually seen, even when factoring in the limited sensitivity of available detectors. Most jetted GRBs will "miss" the Earth and never be seen; only a small fraction happen to be pointed the right way to allow detection. Still, even with these considerations, the rate of GRBs is very small—about once per galaxy per 100,000 years. [cite journal|url=http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004ApJ...607L..17P|author=Podsiadlowski "et al."|year=2004|title=The Rates of Hypernovae and Gamma-Ray Bursts: Implications for Their Progenitors|journal=Astrophysical Journal|volume=607L|pages=17P|doi=10.1086/421347]

hort GRBs

The above arguments apply only to long-duration GRBs. Short GRBs, while also extragalactic, appear to come from a lower-redshift population and are less luminous than long GRBs.cite journal|url=http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2006ApJ...642..989P&db_key=AST&data_type=HTML&format=&high=4322390bbe01196|author=Prochaska "et al."|year=2006|title=The Galaxy Hosts and Large-Scale Environments of Short-Hard Gamma-Ray Bursts|journal=Astrophysical Journal|volume=641|pages=989] They appear to be generally less beamed [cite journal|url=http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2006A%26A...454L.123W&db_key=AST&data_type=HTML&format=&high=4322390bbe02662|author=Watson, D. "et al."|year=2006|title=Are short γ-ray bursts collimated? GRB 050709, a flare but no break|journal=Astronomy and Astrophysics|volume=454|pages=L123–L126 | doi = 10.1051/0004-6361:20065380 ] or possibly not beamed, [cite journal|url=http://lanl.arxiv.org/abs/astro-ph/0603773|author=Grupe, D. "et al."|year=2006|title=Jet Breaks in Short Gamma-Ray Bursts. I: The Uncollimated Afterglow of GRB 050724|journal=Astrophysical Journal|volume=653|pages=462 | doi = 10.1086/508739 ] intrinsically less energetic than their longer counterparts, and probably more frequent in the universe despite being observed rarely.

Progenitors: what causes GRBs?

The immense distances of most gamma-ray burst sources from Earth has made pinning down the nature of the system that produces these explosions extremely difficult. The currently favored model for the origin of most observed GRBs is the collapsar model, [cite journal|url=http://adsabs.harvard.edu/abs/1999ApJ...524..262M|author=MacFadyen, A. I. and Woosley, S.|year=1999|title=Collapsars: Gamma-Ray Bursts and Explosions in "Failed Supernovae"|journal=ApJ|volume=524|pages=262–289 | doi = 10.1086/307790 ] in which the core of an extremely massive, low-metallicity, rapidly-rotating star collapses into a black hole, and the infall of material from the star onto the black hole powers an extremely energetic jet that blasts outward through the stellar envelope. When the jet reaches the stellar surface, a gamma-ray burst is produced.

While the collapsar model has enjoyed a great deal of success, many other models exist that are still seriously considered. Winds from highly magnetized, newly-formed neutron stars (protomagnetars), accretion-induced collapse of older neutron stars, and the mergers of binary neutron stars have all been proposed as alternative models. [cite journal|url=http://adsabs.harvard.edu/abs/2007AIPC..937..521M|author=Metzger, B.|year=2007|title=Proto-Neutron Star Winds, Magnetar Birth, and Gamma-Ray Bursts|journal=AIP Conference Proceedings|volume=937|pages=521–525|doi=10.1063/1.2803618] [cite journal|url=http://adsabs.harvard.edu/abs/1998ApJ...507L..45V|author=Vietri, M. and Stella, L.|year=1998|title=A Gamma-Ray Burst Model with Small Baryon Contamination|journal=ApJ|volume=507|pages=L45–L48 | doi = 10.1086/311674 ] [cite journal|url=http://adsabs.harvard.edu/abs/2006AIPC..836...48M|author=MacFadyen, A. I.|year=2006|title=Late flares from GRBs --- Clues about the Central Engine|journal=AIP Conference Proceedings|volume=836|pages=48–53|doi=10.1063/1.2207856] [cite journal
url=http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1984SvAL...10..177B&db_key=AST&link_type=ABSTRACT&high=4322390bbe18728
author=Blinnikov, S., "et al."
year=1984
title=Exploding Neutron Stars in Close Binaries
journal=Soviet Astronomy Letters
volume=10
pages=177] The different models are not mutually exclusive, and it is possible that different bursts have different progenitors. For example, there is now good evidence that some short gamma-ray bursts (GRBs with a duration of less than about two seconds) occur in galaxies without massive stars, providing strong evidence that this subset of events are associated with a different progenitor population from longer bursts - for example, merging neutron stars. However, in 2007 the detection of 39 short gamma-ray bursts could not be associated with gravitational waves which are thought of as observables of such compact mergers. [cite journal
url=http://arxiv.org/abs/0709.0766
author=LIGO Scientific Collaboration
eprint=0709.0766
title=Search for Gravitational Waves Associated with 39 Gamma-Ray Bursts Using Data from the Second, Third, and Fourth LIGO Runs
year=2007
version=v2]

Emission mechanisms

The means by which gamma-ray bursts convert energy into radiation remains poorly understood, and as of 2007 there is still no generally accepted model for how this process occurs. [cite web|url=http://www.blackwell-synergy.com/doi/abs/10.1111/j.1365-2966.2004.08163.x|title=Gamma-ray bursts from synchrotron self-Compton emission|publisher=blackwell-synergy.com|month=August | year=2004|accessdate=2007-10-12] A successful model of GRBs must explain not only the energy source, but also the physical process for generating an emission of gamma rays which matches the durations, light spectra, and other characteristics observed. [cite web|url=http://antwrp.gsfc.nasa.gov/diamond_jubilee/papers/fishman.html|title=Gamma-Ray Bursts: An Overview|author=Fishman, Gerald J.|publisher=nasa.gov|date=May 22, 1995|accessdate=2007-10-12] The nature of the longer-wavelength (X-ray through radio) afterglow emission that follows gamma-ray bursts has been modeled much more successfully as synchrotron emission from a relativistic shock wave propagating through interstellar space, [cite journal
url=http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1997ApJ...476..232M&db_key=AST&data_type=HTML&format=&high=4322390bbe05056
author=Meszaros, P. and Rees, M.~J.
year=1997
title=Optical and Long-Wavelength Afterglow from Gamma-Ray Bursts
journal=Astrophysical Journal
volume=476
pages=476] [cite journal
url=http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1998ApJ...497L..17S&db_key=AST&data_type=HTML&format=&high=4322390bbe05056
author=Sari, R.; Piran, T.; Narayan, R.
year=1998
title=Spectra and Light Curves of Gamma-Ray Burst Afterglows
journal=Astrophysical Journal Letters
volume=497
pages=L17] but this model has had difficulty explaining the observed features of some observed GRB afterglows (particularly at early times and in the X-ray band) [cite journal|url=http://adsabs.harvard.edu/abs/2006ApJ...642..389N|author=Nousek, J. A. "et al."|year=2006|title=Evidence for a Canonical Gamma-Ray Burst Afterglow Light Curve in the Swift XRT Data|journal=ApJ|volume=642|pages=389–400 | doi = 10.1086/500724 ] , and may be incomplete, or in some cases even inaccurate.

Mass extinction on Earth

Research has been conducted to investigate the consequences of Earth being hit by a beam of gamma rays from a nearby (about 500 light years) gamma ray burst. This is motivated by the efforts to explain mass extinctions on Earth and estimate the probability of extraterrestrial life. Scientists suspect that if a GRB were to occur near our solar system, and one of the beams were to hit Earth, it could cause mass extinctions all over the planet. The GRB would have to be less than 3,000 light years away to pose a danger. [ [http://researchnews.osu.edu/archive/gammaray.htm Deadly Astronomical Event Not Likely To Happen In Our Galaxy, Study Finds ] ] A consensus seems to have been reached that damage by a gamma ray burst would be very limited because of its very short duration, and the fact that it would only cover half the Earth, the other half being in its shadow.Fact|date=June 2008 A sufficiently close gamma ray burst would however, result in serious damage to the atmosphere, shutting down communications (due to electro-magnetic disturbances), perhaps instantly wiping out half the ozone layer, and causing nitrogen-oxygen recombination, thereby generating acidic nitrogen oxides. These effects could diffuse across to the other side of the Earth, severely diminish the global food supply, and result in long-term climate and atmospheric changes and a mass extinction, reducing the global population to perhaps 10% of what it can now support. [B.S. Lieberman, University of Kansas, said this on the episode "Human Extinction" in the third season of "Earth Investigated" aired by the National Geographic Channel] The damage from a gamma ray burst would probably be significantly greater than a supernova at the same distance.

The idea that a nearby gamma-ray burst could significantly affect the Earth's atmosphere and potentially cause severe damage to the biosphere was introduced in 1995 by physicist Stephen Thorsett, then at Princeton University. [cite journal|author=Thorsett, S. E.|title=Terrestrial implications of cosmological gamma-ray burst models|accessdate=2007-09-15|date=05/1995|journal=Astrophysical Journal|url=http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1995ApJ...444L..53T|doi=10.1086/187858|volume=444|pages=L53] In 2005, scientists at NASA and the University of Kansas released a more detailed study which suggested that the Ordovician-Silurian extinction events which occurred 450 million years ago could have been triggered by a gamma-ray burst. They did not have direct evidence to suggest that such a burst resulted in the ancient extinction, rather the strength of their work was their atmospheric modeling, essentially a "what if" scenario. The scientists calculated that gamma-ray radiation from a relatively nearby star explosion, hitting the Earth for only ten seconds, could deplete up to half of the atmosphere's protective ozone layer, the recovery for which would take at least five years. With the ozone layer damaged, ultraviolet radiation from the Sun would kill much of the life on land and near the surface of oceans and lakes, disrupting the food chain. While gamma-ray bursts in our Milky Way galaxy are indeed rare, NASA scientists estimate that at least one nearby event has probably hit the Earth in the past billion years, with life on Earth being at least 3.5 billion years old. Dr. Bruce Lieberman, a paleontologist at the University of Kansas, originated the idea that a gamma-ray burst specifically could have caused the great Ordovician extinction. He said, "We do not know exactly when one came, but we're rather sure it did come - and left its mark. What's most surprising is that just a 10-second burst can cause years of devastating ozone damage." [cite web|url=http://www.nasa.gov/vision/universe/starsgalaxies/gammaray_extinction.html|title=Explosions in Space May Have Initiated Ancient Extinction on Earth|accessdate=2007-09-15|date=June 4, 2005|publisher=nasa.gov]

Comparative work in 2006 on galaxies in which GRBs have occurred suggests that metal-deficient galaxies are the most likely candidates. The likelihood of the metal-rich Milky Way galaxy hosting a GRB was estimated at less than 0.15%, significantly reducing the likelihood that a burst had caused mass extinction events on Earth. [cite web|url=http://www.astrobio.net/news/modules.php?op=modload&name=News&file=article&sid=1932&mode=thread&order=0&thold=0|title=One Less Thing to Worry About|publisher=astrobio.net|accessdate=2007-09-15|date=April 19, 2006]

The Wolf-Rayet star WR 104, located 8000 light years from Earth, has been found to have a rotational axis aligned within 16° of the solar system. The chances of it producing a gamma ray burst are small, and the effects on earth from such an event are still not fully understood. [ [http://www.badastronomy.com/bablog/2008/03/03/wr-104-a-nearby-gamma-ray-burst/ badastronomy.com] ]

Gamma Ray Bursts and Quantum Gravity

It is widely speculated that if Loop quantum gravity (LQG) Theory is correct then a measurable "diffraction" of particles of like frequency from a burst will occur; if such an effect is observed it may offer proof of the existence of quantum gravity. [cite journal|url=http://arxiv.org/abs/hep-th/0108061v3|title="Loop quantum gravity and light propagation"|author=Jorge Alfaro, Hugo A. Morales-Técotl, Luis F. Urrutia 2002]

Notable GRBs

GRBs of significant historical or scientific importance include:
* 670702: On July 2, 1967, the first GRB is detected by the Vela 4 satellite. [cite journal|author=Strong, Klebesadel, and Olson|date=February 15, 1974|title=A Preliminary Catalog of Transient Cosmic Gamma-Ray Sources Observed by the "Vela" Satellites|journal=The Astrophysical Journal|publisher=American Astronomical Society | volume = 188 | pages = L1 | doi = 10.1086/181415 ] [See also: [http://antwrp.gsfc.nasa.gov/htmltest/jbonnell/www/grbhist.html#firstburst A Brief History of the Discovery of Cosmic Gamma-Ray Bursts] , J.Bonnell, April 17, 1995 (retrieved Aug 28, 2008), and, " [http://apod.nasa.gov/apod/ap000702.html Gamma-Ray Burst: A Milestone Explosion] ", Astronomy Picture of the Day, 2000 July 2, (retrieved Aug 28, 2008)]
* 970228: The first GRB with a successfully detected afterglow. The location of the afterglow was coincident with a very faint galaxy, providing strong evidence that GRBs are extragalactic. [cite journal|author=Esin AA, Blandford R|title=Dust Echoes from Gamma-Ray Bursts|journal=Astrophysical Journal|volume=534|issue=2|year=2000|pages=L151–L154|pmid=10813670|doi=10.1086/312670]
* 970508: The first GRB with a measured redshift (the extent to which the radiation is redshifted allows astronomers to calculate an estimate of the distance of the event), 0.835. This confirmed unambiguously that GRBs are extragalactic. [cite journal|author=Reichart, Daniel E.|title=The Redshift of GRB 970508|date=February 19, 1998|journal=The Astrophysical Journal|publisher=American Astronomical Society | volume = 495 | pages = L99 | doi = 10.1086/311222 ]
* 971214: In 1997, this was believed by some to be the most energetic event in the universe. This claim has since been discredited. [cite journal|url=http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999ApJ...519L..17S&db_key=AST|author=Sari, R.; Piran, T.; Halpern, J. P.|year=1999|title=Jets in Gamma-Ray Bursts|journal=Astrophysical Journal|volume=519|pages=L17–L20 | doi = 10.1086/312109 ] [cite journal|url=http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001ApJ...562L..55F&db_key=AST|author=Frail, D.A. et al.|year=2001|title=Beaming in Gamma-Ray Bursts: Evidence for a Standard Energy Reservoir|journal=Astrophysical Journal|volume=562|pages=L55–L58 | doi = 10.1086/338119 ]
* 980425: The first GRB with an observed associated supernova (1998bw), providing strong evidence of the link between GRBs and supernovae. The GRB itself was very unusual for being extremely underluminous. Also the closest GRB observed to date. [cite web|url=http://www.space.com/scienceastronomy/astronomy/gammaray_bursts_010522-1.html|title=Cosmic Cannon: How an Exploding Star Could Fry Earth|date=June 19, 2001|publisher=space.com|accessdate=2007-10-10]
* 990123: This GRB had the optically brightest afterglow measured before 080319B, momentarily reaching or exceeding a magnitude of 8.9, which would be visible with an ordinary pair of binoculars, despite its distance of nearly 10 billion light years. This was also the first GRB for which optical emission was detected before the gamma-ray emission had ceased. [cite web|url=http://science.nasa.gov/newhome/headlines/ast27jan99_1.htm|publisher=nasa.gov|title=GOTCHA! The Big One That Didn't Get Away|date=January 27, 1999|accessdate=2007-10-10]
* 030329A: An extremely close (z=0.168), [cite web|url=http://gcn.gsfc.nasa.gov/gcn3/2053.gcn3|author=N. Caldwell, et al. |title=GCN 2053, GRB 030329, optical spectroscopy] and therefore extremely bright GRB, with an unambiguous supernova association. [cite web|url=http://gcn.gsfc.nasa.gov/gcn3/2120.gcn3|author=T. Matheson, et al.|title=GCN 2120, GRB 030329: Supernova Confirmed] GRB 030329 was so bright that its gamma radiation ionized the Earth's upper atmosphere. [cite web|url=http://gcn.gsfc.nasa.gov/gcn3/2176.gcn3|author=P.W. Schnoor, et al.|title=GCN 2176, GRB030329 observed as a sudden ionospheric disturbance (SID)]
* 050509B: The first short GRB with a host association. Provided evidence that (some) short GRBs, unlike long GRBs, occur in old galaxies and do not have accompanying supernovae. [cite web|url=http://news.bbc.co.uk/2/hi/science/nature/4537905.stm|title=Blast hints at black hole birth|publisher=bbc.co.uk|accessdate=2007-10-10|date=May 11, 2005]
* 050724: A thoroughly observed short gamma-ray burst with an afterglow suggesting the demise of a neutron star orbiting a black hole. [cite web|url=http://www.nasa.gov/mission_pages/swift/main/blackhole_meal.html|title=Cosmic Explosion Could Be Black Hole Swallowing Neutron Star|publisher=nasa.gov|date=December 14, 2005|accessdate=2007-10-10]
* 050904: The most distant GRB with a securely measured distance, at a redshift of 6.29 (13 billion light-years). [cite web|url=http://swift.gsfc.nasa.gov/docs/swift/news/2005/05-259.html|title=MOST DISTANT EXPLOSION DETECTED, SMASHES PREVIOUS RECORD|publisher=nasa.gov|date=September 12, 2005|accessdate=2007-10-10]
* 060218: A low-redshift GRB with an accompanying supernova. [cite web|url=http://www.space.com/scienceastronomy/060830_grb_supernova.html|title=Strange Exploding Star Unlocks Supernova Secrets|accessdate=2007-10-10|date=August 30, 2006]
* 060505: The first, well-observed, long duration GRB not accompanied by a bright supernova. [cite web|url=http://arxiv.org/abs/astro-ph/0703407v2|title=Spatially resolved properties of the GRB 060505 host: implications for the nature of the progenitor|publisher=arxiv.org|date=march 15, 2007|accessdate=2007-10-10]
* 060614: Another recent gamma-ray burst not accompanied by an observable supernova. [cite web|url=http://www.nasa.gov/home/hqnews/2006/dec/HQ_06373_Hybrid_Burst.html|title=NASA Satellite Discovers New Kind of Black Hole Explosion
publisher=NASA|date=december 20, 2006|accessdate=2007-11-11]
* 080319B: Extremely intense GRB with the brightest visible afterglow ever (at 5th magnitude, bright enough to see with the naked eye). [cite web|url=http://gcn.gsfc.nasa.gov/other/080319.gcn3|title=Gamma Ray Burst Coordinates Network
publisher=NASA|date=March 19, 2008|accessdate=2008-03-20] It is the most energetic event detected by Swift so far and the most luminous optical source ever seen. [cite journal
url=http://arxiv.org/abs/0803.3215
author=Bloom, J. S., "et al."
year=2008
title=Observations of the Naked-Eye GRB 080319B: Implications of Nature's Brightest Explosion
journal=Astrophysical Journal
pages=submitted]

ee also

* Supernova
* Collapsar
* Soft gamma repeater
* Gamma-ray astronomy
* Terrestrial gamma-ray flashes
* Stellar evolution
* Black hole

References

External links

;GRB Catalogs and Circulars
* [http://grb.sonoma.edu Gamma-ray Burst Real-time Sky Map based on Swift data]
* [http://grad40.as.utexas.edu/grblog.php GRBlog: A Gamma-Ray Burst Database at University of Texas]
* [http://gcn.gsfc.nasa.gov/ Gamma Ray Burst Coordinates Network]
* [http://grbox.net GRBOX] , a feature-rich online (grbox.net) catalog of gamma-ray bursts and their properties for public use
* [http://www.mpe.mpg.de/~jcg/grbgen.html Greiner's GRB Catalog]

;GRB General Information
* [http://astro.caltech.edu/~ejb/faq.html Gamma-ray burst FAQ from Caltech]
* [http://swift.sonoma.edu/about_swift/grbs.html Gamma-ray burst information from NASA/Swift]

;GRB Mission Sites
* [http://swift.gsfc.nasa.gov/docs/swift/swiftsc.html Official NASA Swift Homepage: The Swift Gamma-Ray Burst Mission]
* [http://www.swift.ac.uk/ UK Swift Science Data Centre]
* [http://www.swift.psu.edu/ Swift Mission Operations Center at Penn State]
* [http://space.mit.edu/HETE/ HETE-2]
* [http://www.esa.int/science/integral INTEGRAL]
* [http://www.batse.msfc.nasa.gov/batse/ BATSE: Burst and Transient Source Explorer]
* [http://www-glast.stanford.edu/ Glast] Current launch date: May 20, 2008
* [http://agile.rm.iasf.cnr.it/index.html Agile]
* [http://exist.gsfc.nasa.gov/ EXIST: Energetic X-ray Survey Telescope]

;GRB Follow-up Programs
* [http://www.physics.unc.edu/skynet/observatories/prompt/ PROMPT: Panchromatic Robotic Optical Monitoring and Polarimetry Telescopes] (Wiki entry)
* [http://www.raptor.lanl.gov/ RAPTOR: Rapid Telescopes for Optical Response]
* [http://rotse1.physics.lsa.umich.edu/ ROTSE: Robotic Optical Transient Search Experiment]
* [http://pairitel.org/ PAIRITEL: Peters Automated Infrared Imaging Telescope]
* [http://observ.pereplet.ru/ MASTER: Mobile Astronomical System of the Telescope-Robots]
* [http://astro.berkeley.edu/~bait/kait.html KAIT: The Katzman Automatic Imaging Telescope]
* BOOTES

;News Articles and Media
* [http://www.pbs.org/wgbh/nova/gamma/ PBS NOVA: Death Star (gamma-ray bursts)]
* [http://hubblesite.org/newscenter/newsdesk/archive/releases/1998/17/text/ GRB 971214: Most energetic event in the universe]
* [http://imgsrc.hubblesite.org/hu/db/1998/17/videos/b/formats/high_real.ram GRB 971214: Space Science Update Webcast (RealMedia)]
* [http://imgsrc.hubblesite.org/hu/db/1998/17/videos/a/formats/low_quicktime.mov Animation of Gamma Ray Burst (Quicktime)]
* [http://astro.berkeley.edu/~jbloom/pr0326.html GRB 980326: Evidence for a massive star connection]
* [http://www.npr.org/templates/story/story.php?storyId=4679036 Gamma ray bursters] segment of Science Friday, 3 June 2005 (RealAudio)
* [http://news.bbc.co.uk/1/hi/sci/tech/4237800.stm Most distant cosmic blast sighted] (BBC reports a registered GRB from about 13 billion light years away)
* [http://www.eso.org/outreach/press-rel/pr-2003/pr-16-03.html Cosmological Gamma-Ray Bursts and Hypernovae Conclusively Linked] (ESO)
* [http://science.nasa.gov/headlines/y2008/21mar_nakedeye.htm GRB 080319B Naked Eye Burst (2008-03-19)] reported by NASA, from 7.5 billion light years and [http://grb.fuw.edu.pl/pi/ot/grb080319b/normal.html Animation of the event]
* [http://www.orionspace.net/08/21-mar-2008-swift.html New Gamma Ray Burst is Most Distant Naked Eye Object.]