Gamma-ray burst

This article covers cosmic bursts of gamma rays. For the atmospheric gamma-ray bursts see Terrestrial gamma-ray burst .

Artist's impression of a bright gamma-ray burst in a star formation. The energy from the explosion radiates in two narrow, oppositely directed jets.

Gamma-ray bursts , gamma-ray bursts , gamma-ray bursts , or gamma ray explosions ( English gamma-ray bursts , often abbreviated GRB ) are bursts of energy very high performance in the universe , of which large amounts of electromagnetic radiation out.

The origin of the gamma-ray bursts has not yet been fully clarified. A gamma-ray burst was observed for the first time on July 2, 1967 with the US Vela surveillance satellites , which were actually used to detect aboveground atomic bomb tests . It was not until 1973 that scientists at the Los Alamos National Laboratory in New Mexico determined that the rays came from deep space using the data from the satellites.

The term “gamma-ray burst” has probably become established because the Vela satellites were designed and equipped to detect the gamma radiation from nuclear weapon explosions. Electromagnetic radiation with photon energies in the keV range and higher is often generally referred to as gamma radiation if its source and origin are not known. Gamma flashes are not concerned with gamma radiation in the narrower, nuclear physical sense.

Observations

Gamma-ray bursts release more energy in ten seconds than the sun does in billions of years. For the duration of its glow, a gamma-ray burst is brighter than all other gamma-ray sources in the sky. Gamma-ray bursts also have an afterglow in the optical and X-ray spectrum that slowly fades over periods of the order of days and weeks.

The brightest gamma-ray flash observed to date was registered by NASA's Swift research satellite on March 19, 2008. The outbreak came from an object 7.5 billion light-years away from Earth. He was 2.5 million times brighter than the fluorescent strongest previously observed supernova and could be the first GRB ( English being seen gamma-ray burst) with the naked eye. This explosion was cataloged under the number GRB 080319B .

Optical afterglow of the GRB-990123 gamma -ray flash (light point in the white square and enlarged section). The curved object above is the galaxy it came from. This was probably deformed by a collision with another galaxy.

The radiation from gamma-ray bursts can not penetrate the earth's atmosphere unchanged. Hence, gamma-ray bursts can

• directly only with space telescopes
• or indirectly through measurements of the secondary radiation showers triggered in the atmosphere.

Because of their short duration and high luminosity and because of the low spatial resolution of the satellite telescopes, the gamma-ray bursts could neither be assigned to known (visible) sources nor credible assumptions about their causes. At first, the sources of the lightning were suspected to be within our Milky Way , because events of such brightness did not appear to be physically explainable at a further distance. However, from their uniform distribution over the entire sky, one could conclude that these were extragalactic events. Otherwise, they would have to cluster in the plane of the Milky Way, where most of the stars in the Milky Way are located, or, if they belonged to the halo of the Milky Way, in the direction of the galactic center.

A significant advance was achieved through the very rapid localization of the gamma-ray bursts, so that other telescopes can be automatically pointed to its position in the sky during the gamma-ray burst. With the help of the X-ray satellite BeppoSAX , the afterglow of gamma-ray flashes in the X-ray range could be observed for the first time in 1997. Due to the much more precise position determination in X-ray astronomy , it was possible to make targeted follow-up observations in UV and visible light and to assign them to known sources. Distant galaxies were found at the locations of the gamma-ray bursts and it was thus possible to directly prove that gamma-ray bursts have extragalactic sources.

Duration

The duration of gamma-ray flashes is a few seconds to a maximum of a few minutes; two known exceptions are GRB 060218 with 33 minutes and GRB 110328A (Sw 1644 + 57), which achieved a record duration of several weeks.

GRB can be divided into two different classes according to their duration. The long GRBs last about 35 seconds on average, and the ultra- long GRBs more than 10,000 seconds. In some very long GRBs, a core collapse supernova could be observed at the same time as the gamma-ray flash .

On September 4, 2005, NASA's Swift satellite registered an outbreak that flashed for 200 seconds, making it one of the long GRBs. It came from a region 12.7 billion light years away, that is, from the time of the relatively young universe . This gamma-ray burst with the designation GRB 050904 is one of the most distant GRBs and at that time represented the second oldest documented event in the universe.

In contrast, short GRBs last less than two seconds. The optical afterglow of this GRB is also much shorter than that of the long GRB. It was first observed in 2005. Short GRBs usually have harder X-ray spectra than the long ones. About 30% of all short GRBs are followed by a highly variable X-ray burst lasting up to 100 seconds. This different behavior within the class of the short GRB suggests more than one mechanism of origin.

On December 27, 2004 (21:30 UTC ) Earth was hit by the gamma and X-ray eruption GRB 041227 . A neutron star had released more energy in 0.2 seconds than the sun did in 150,000 years. The wave front at a distance of about 50,000 light years from the source was more intense than the strongest burst of radiation from our sun ever recorded. Researchers in Australia reported that the giant explosion of the neutron star SGR 1806-1820 made it brighter than the full moon for a tenth of a second.

Advance break

→ Main article : Gamma Ray Burst Precursor

Approximately 15 percent of all gamma ray bursts show one or more precursors ( precursor ). This is gamma radiation that occurs up to 100 seconds before the main outbreak and has about 100 times less luminosity. Before the main eruption there is usually a phase in which no radiation is detected. The spectrum corresponds to that of the main eruption. If several precursors are observed, there are rest phases of around 10 seconds between them.

spectrum

Spectrum of the gamma-ray burst 910,503th Logarithmic is plotted the spectral photon flux density N (E) with E ² scaled by the photon energy E . The red and blue function graph shows the course of the phenomenological formula shown here.

The radiation shows a continuous spectrum with photon energies of less than 1  keV up to the MeV range. Most spectra can be described by dividing them into two areas. In the range of low energies up to a few hundred keV (depending on the GRB), the frequency of the photons decreases exponentially with increasing energy. In the area of ​​high energies, the frequency of a hyperbola continues to decrease . Because of the wide range of energies that occur, the frequencies for the individual channels differ by many powers of ten. Therefore, a linear representation of the entire spectrum in one diagram does not make sense. A power quantity (frequency · energy²) is better plotted against the energy in a double logarithmic manner. This representation shows a maximum for most of the spectra, namely at the photon energy at which the greatest power was received. This peak energy is characteristic of the gamma-ray burst and averages around 250 keV for the gamma-ray bursts investigated by BATSE .

The exact phenomenological model for the continuous spectrum is:

${\displaystyle N(E)\sim {\begin{cases}{E^{\alpha }\exp \left({-{\frac {E}{E_{0}}}}\right)},&{\text{für }}E\leq (\alpha -\beta )E_{0}\ \\{\left[{\left({\alpha -\beta }\right)E_{0}}\right]^{\left({\alpha -\beta }\right)}E^{\beta }\exp \left({\beta -\alpha }\right)},&{\text{für }}E>(\alpha -\beta )E_{0}\ \end{cases}}.}$

• ${\displaystyle \alpha }$and are free parameters; ${\displaystyle \beta }$ ${\displaystyle \alpha \approx -1,\beta \approx -2}$
• ${\displaystyle E_{0}}$is linked to the peak energy via . ${\displaystyle E_{p}}$ ${\displaystyle E_{0}={\frac {E_{p}}{2+\alpha }}}$

For and results: ${\displaystyle \alpha =-1}$ ${\displaystyle \beta =-2}$

${\displaystyle N(E)={\begin{cases}{E^{-1}\exp \left({-{\frac {E}{E_{p}}}}\right)},&{\text{für }}E\leq E_{p}\\E_{p}E^{-2}e^{-1},&{\text{für }}E>E_{p}\ \end{cases}}}$

Weak individual spectral lines are superimposed on the continuum, but these are strongly Doppler broadened . Such lines on the continuous spectrum give an insight into the physical processes involved in the creation of radiation. The strong blue shift means that the explosive material is moving towards the observer at a highly relativistic speed. The Doppler broadening results from the strong thermal movement due to the high temperature of the emitting material.

The spectrum is not constant for the duration of the GRB, but can be approximated at all times using the same functions mentioned above, only the parameters change over time. In general, the peak energy and thus the hardness of the spectrum decrease during the duration of the gamma-ray flash, but can also briefly increase again during the course of the flash with bursts of intensity.

Possible emergence

Due to the short duration of the gamma-ray burst, the area from which it was emitted cannot be very large. The diameter of a slow object (less than 10% of the speed of light ) is at most equal to the shortest change in brightness multiplied by the speed of light; due to relativistic effects, this area can be somewhat larger, but is still quite small. Special supernova explosions, so-called hypernovae , are therefore a possible cause of gamma-ray flashes. Another possible cause of a gamma-ray flash is merging neutron stars .

If a gamma-ray burst were to radiate evenly in all directions, the gamma-ray burst GRB-990123 from January 1999 (see picture above) would have had to have a radiation power of over 10 ⁴⁵  watts , corresponding to 2.5 · 10 ¹⁸ times the solar luminosity , i.e. 2, 5  trillion suns. Even quasars only get 10 ⁴⁰  watts.

It is therefore assumed that a gamma-ray burst is only emitted in two narrow, opposing, conical areas with an opening angle of a few degrees, i.e. the radiation is focused like a lighthouse. This reduces the radiation power required to explain the observed brightness by approx. 3 powers of ten, but it is still extremely high. In addition, the focus can be used to explain the violence of the bursts of energy without violating fundamental physical principles. Finally, the gamma-ray burst is caused by shock waves in the gas of the supernova explosion , which propagates at almost the speed of light . The total amount of energy released is roughly in the same order of magnitude as that of a supernova, but the supernova emits most of its energy in the form of neutrinos . Model calculations show that the observed brightness curve of the gamma-ray bursts fits well with the assumptions. The observations made by GRB 080319B (see above) show that within the conical areas there is still a smaller, even more 'pointed' jet that practically no longer shows any widening in diameter. In the aforementioned gamma-ray burst, the earth was located exactly within this 'laser beam', which should represent a rare event: It is possible that there is such a second beam with every gamma-ray burst, but this can only be observed when the earth or the measuring device is inside this narrow cone of radiation is located. So far this has only been the case with GRB 080319B.

Illustration of a massive star collapsing into a black hole . The released energy in the form of jets along the axis of rotation forms a gamma-ray burst.

The difference to a normal supernova is explained by the fact that particularly massive stars with more than 20  solar masses form a hypernova , the central core area of ​​which collapses into a rapidly rotating black hole . The surrounding gas runs around the black hole in an accretion disk and heats up very strongly when it falls. Gas jets are then ejected perpendicular to the plane of the disk and generate the gamma-ray bursts. The merger of two neutron stars leads to similar results.

Even if a connection with supernovae has long been suspected, it was not possible until 1997 to link a gamma-ray burst directly to such a star death. The High Energy Transient Explorer (HETE) satellite observed a gamma-ray burst, the source of which was found to be the collapse of a star 15 times the mass of the Sun.

For a part of the GRB with a long eruption, a supernova was found at the same location, which lit up a few hours later. All confirmed matches are a naked core collapse supernova of the Ic-b1 type. These developed stars have produced all elements down to iron in their core and have lost at least the hydrogen-rich atmospheric layers through stellar wind or interaction in a binary star system. However, a corresponding gamma-ray flash was found only in a very small proportion of the Ic-b1 supernovae. This can be explained firstly by the narrow cone in which the gamma radiation is emitted and in which only a small part of all supernovae happens to be directed towards Earth; second, the energy of the gamma-ray burst is not always sufficient to penetrate the star's remaining atmosphere. On the other hand, supernovae have not been found for all long gamma-ray bursts. There should therefore be other channels for long gamma-ray bursts.

The following events are associated with the formation of long gamma-ray bursts:

• A core collapse supernova associated with the formation of a neutron star or black hole
• A hypothetical hypernova associated with the creation of a black hole

For a short time, astronomers believed that magnetars (unstable young neutron stars surrounded by an extremely strong magnetic field) could be the source of particularly short gamma-ray bursts. But the magnetar theory is probably wrong, as further observations in 2005 showed. The HETE-2 probe , which has been in space since October 2000, captured a gamma-ray burst of just 70 milliseconds on July 9, 2005. Scientists rushed to align the Hubble and Chandra space telescopes and the Danish 1.5-meter telescope in La Silla, Chile, with the explosion. In this way the first images of the afterglow of a short gamma-ray flash in the area of ​​optical light were created.

Three scenarios are discussed for the formation of short gamma-ray bursts

• The merging of two neutron stars in a binary star system through collision
• The merging of a neutron star and a black hole in a binary star system through collision
• The collapse of a white dwarf (thermonuclear supernova, type Ia) when the maximum mass is exceeded by accretion ( Chandrasekhar limit )

The emission of X-rays following the outbreak could come from the loss of rotational energy of a magnetar that has just formed .

On October 16, 2017, the LIGO collaboration announced that a gravitational wave signal from the collision of two neutron stars had been discovered for the first time . At the same time, it was associated with a short gamma-ray flash (GRB 170817A) and could be observed in the optical and other electromagnetic wave ranges. This was the first evidence of a presumed connection between short gamma-ray bursts and the collision of two neutron stars.

With the help of a computer simulation, scientists at the Max Planck Institute for Gravitational Physics have examined the merging of two neutron stars to form a black hole in more detail and have been able to show for the first time that a jet-shaped structure is formed along the axis of rotation through the reorganization of the magnetic field during the merging Internal gamma-ray bursts can arise. For the simulation, the scientists had solved Einstein's field equations and the equations of magnetohydrodynamics for this scenario.

Speculation about the consequences of nearby gamma-ray bursts

Possible mechanism

The immediate, immediate damage caused by a gamma-ray burst aimed directly at the earth would be limited according to the results of a study, since gamma-ray bursts are usually only brief and a large part of the gamma rays do not reach the earth. Gamma radiation is absorbed in the atmosphere , producing nitric oxide , among other things . Also, the side of the earth facing away from the gamma-ray burst would not be affected immediately by the gamma-ray burst, since the gamma radiation cannot penetrate the planet. However, a sufficiently close gamma-ray burst forms so much nitrogen oxide in the atmosphere that the ozone layer would be severely damaged. This could also have a strong influence on the untouched earth side.

Historic mass extinction

One of the largest mass extinctions in Earth's history may have been triggered by a gamma-ray flash in the Milky Way . For example, there is speculation about an event 443 million years ago (end of the Ordovician ). As a result of a gamma-ray flash, the sun's UV radiation would have penetrated the uppermost water layers of the primordial oceans unhindered after the ozone layer had been destroyed. Organisms that lived near the surface of the water could have been killed there (land organisms did not exist at that time). As an indication of such a scenario, it is stated that at the end of the Ordovician, many trilobites living near the water surface died out.

Future dangers

A group of scientists at Ohio State University was tasked with finding out what the consequences would be if a nearby gamma-ray burst (about 500 light years) hit Earth. The investigation should also help to clarify mass extinctions on earth and to be able to estimate the probability of extraterrestrial life . As a result, scientists suspect that a gamma-ray burst that originates near our solar system and hits Earth could trigger mass extinctions across the planet. The expected severe damage to the ozone layer would collapse the global food supply and lead to long-lasting changes in the climate and atmosphere. That would cause a mass extinction on earth and reduce the world population to, for example, 10% of its current value.

The damage caused by a gamma-ray burst would be significantly greater than that caused by a supernova that occurs at the same distance as the gamma-ray burst. According to the study, gamma-ray bursts beyond 3,000  light years pose no danger.

Noteworthy gamma-ray bursts

GRB of particular historical or scientific importance:

• 670702 - July 2, 1967: The first GRB observed.
• 970228 - February 28, 1997: The first GRB to successfully detect afterglow.
• 970508 - May 8, 1997: The first GRB with a precisely determined redshift (a value that enables astronomers to determine the distance to an event or object).
• 980425 - April 25, 1998: The first GRB observed in connection with a supernova (SN 1998bw); showed a close relationship between SN and GRB.
• 990123 - January 23, 1999: The first GRB to detect an emission in the visible range (see picture above).
• 041227 - December 27, 2004: The earth is hit by a huge burst of gamma rays, the wave front of which emanated from a magnetar (SGR 1806–1820) 50,000 ly away.
• 050509B - May 9, 2005: The first short GRB to identify the body of origin (supported the theory that short GRBs are unrelated to supernovae).
• 050724 - July 24, 2005: A short GRB whose origin was found to be a neutron star orbiting a black hole.
• 050904 - September 4, 2005: An old distance record for a GRB with a redshift of 6.29 (12.7 billion light years).
• 080319B - March 19, 2008: Brightest GRB and brightest supernova discovered to date ( absolute brightness : −36 mag); also the first GRB that could be observed with the naked eye ( apparent magnitude : 5.76 mag); at the same time the most distant object that has ever been observed with the naked eye (7.5 billion light years).
• 080913 - September 13, 2008: The old distance record for a GRB with a redshift of 6.7 (12.8 billion light years).
• 090423 - April 23, 2009: The most distant GRB with a redshift of 8.2 (13.035 billion light years) and thus the oldest documented event in the universe (approx. 630 million years after the Big Bang). He was discovered with Swift and the GROND at the La Silla Observatory.
• 100621A - June 21, 2010: The absolutely strongest gamma-ray flash that has been recorded; this made the Swift measuring instruments fail; with 143,000 (X-ray) photons / s stronger than the previous record (GRB 080916C).
• 110328A - March 28, 2011: The longest-running GRB to date was discovered with Swift in the Draco constellation . The phenomenon lasted more than a week.
• 130427A - April 27, 2013: The event could be detected by space telescopes and terrestrial telescopes in the Leo and is considered to be the most energetic and longest lasting GRB to date.
• 130603B - June 3, 2013: Registered by the Swift satellite and the Wind probe (with its Transient Gamma-Ray Spectrometer). Likewise, the region was observed by the Hubble Space Telescope nine days before and 30 days after the eruption. On the third day after the eruption, the X-ray flux in the region was measured using the XMM-Newton X-ray satellite .
• GRB 170817A - August 17, 2017: In this gamma-ray flash, a gravitational wave could be measuredsimultaneously for the first time.

See also

• Kilonova
• Low Luminosity Gamma Ray Burst
• Fast radio flash

literature

• David Alexander Kann, Steve Schulze and Sylvio Klose: Cosmic gamma ray bursts. New discoveries and new puzzles in the era of the Swift gamma satellite. In: Stars and Space. 12/2007, p. 42.
• Neil Gehrels , Luigi Piro, Peter JT Leonard: The strongest explosions in the universe. In: Spectrum of Science. 03/2003, p. 48.
• Deadly star explosion. In: Astronomy Today. 01-02 / 2004, p. 13.
• JS Villasenor u. a .: Discovery of the short Gammaray burst GRB 050709. In: Nature. 437, pp. 855-858 (October 6, 2005). arxiv : astro-ph / 0510190 .
• P. Mészaros: Theories of Gamma-Ray Bursts. In: Annual Review of Astronomy and Astrophysics. Vol. 40, pp. 137-169 (2002), doi: 10.1146 / annurev.astro.40.060401.093821 .
• J. van Paradijs, C. Kouveliotou, & R. Wijers: Gamma-Ray Burst Afterglows . Annual Review of Astronomy and Astrophysics, Vol. 38, pp. 379-425 (2000), doi: 10.1146 / annurev.astro.38.1.379 .
• E. Fenimore: Gamma-ray bursts - 30 years of discovery. AIP Press, Melville 2004, ISBN 0-7354-0208-6 .
• Gilbert Vedrenne, et al .: Gamma-ray bursts - the brightest explosions in the universe. Springer, Berlin 2009, ISBN 978-3-540-39085-5 .

Web links

Commons : gamma-ray bursts  - collection of images, videos and audio files

• www.wissenschaft.de: When gamma-ray bursts die . - Swift satellite observes transition from lightning to afterglow for the first time
• Swift: Gamma-ray burst Real-time Sky Map . - based on data from NASA's Swift satellite
• NASA: Gamma-Ray Burst Coordinates Network .
• The biggest explosions in the universe bbc.com

Videos

• What is a hypernova? from the alpha-Centauri television series(approx. 15 minutes). First broadcast on Dec 6, 2006.
• Are black holes merging? from the alpha-Centauri television series(approx. 15 minutes). First broadcast on May 27, 2001.
• What is the superflare of December 27, 2004? from the alpha-Centauri television series(approx. 15 minutes). First broadcast on Sep 27 2006.

Individual evidence

1. ↑ A Stellar Explosion You Could See on Earth! NASA , March 21, 2008
2. ↑ Eliot Quataert, Dan Kasen: Swift 1644 + 57: The Longest Gamma-ray Burst? In: Astrophysics. Solar and Stellar Astrophysics . 2011, arxiv : 1105.3209 .
3. ↑ Most Distant Explosion detected . NASA, September 12, 2005
4. ↑ Gamma Ray Bursts - Gamma lightning hit earth . astronews.com, February 21, 2005
5. ↑ nasa.gov
6. ↑ Maria Grazia Bernardini et al .: How to switch on and off a Gamma-ray burst through a magnetar . In: Astrophysics. Solar and Stellar Astrophysics . 2013, arxiv : 1306.0013v1 .
7. ^ ^{A b} F. Ryde: Spectral Aspects of the Evolution of Gamma-Ray Bursts . In: Gamma-Ray Bursts: The First Three Minutes , ASP Conference Series, Vol. 190, E S.109, bibcode : 1999ASPC..190..103R
8. ↑ The evaluation of the BATSE measurements resulted in values ​​for mainly between −1.25 and −0.25 and for 2.12 ± 0.3 ${\displaystyle \alpha }$ ${\displaystyle \beta }$
9. ↑ LA Ford, DL Band, JL Matteson, MS Briggs, GN Pendleton, RD Preece: BATSE observations of gamma-ray burst spectra. 2: Peak energy evolution in bright, long bursts . In: Astrophysical Journal , Part 1 ( ISSN  0004-637X ), vol. 439, no. 1, p. 307-321, bibcode : 1995ApJ ... 439..307F
10. ↑ M. Modjaz: Stellar forensics with the supernova-GRB connection. Ludwig Biermann Award Lecture 2010 . In: Astronomical News . tape 332 , no. 5 , 2011, p. 434–457 , doi : 10.1002 / asna.201111562 .
11. ↑ Gamma Ray Bursts - Cause Riddle Solved? astronews.com, May 17, 2002
12. ↑ Gamma Ray Bursts - New Evidence for Hypernova Thesis . astronews.com, November 13, 2003
13. ^ N. Bucciantini, BD Metzger, TA Thompson, E. Quataert: Short GRBs with Extended Emission from Magnetar Birth: Jet Formation and Collimation . In: Astrophysics. Solar and Stellar Astrophysics . 2011, arxiv : 1006.4668v1 .
14. ↑ Gamma Ray Bursts - Solved the mystery of the short flashes of gamma rays . astronews.com, October 6, 2005.
15. ↑ Neutron stars: When neutron stars collide . astronews.com, March 31, 2006
16. ^ BP Abbott et al. a .: GW170817: Observation of Gravitational Waves from a Binary Neutron Star Inspiral, Phys. Rev. Lett., Volume 119, 2017, p. 161101, abstract
17. ↑ A. Goldstein et al. a .: An Ordinary Short Gamma-Ray Burst with Extraordinary Implications: Fermi-GBM Detection of GRB 170817A, Astrophysical Journal Letters, Volume 848, 2017, No. 2, Abstract , published October 16, 2017
18. ↑ Gamma Ray Bursts - Colliding Neutron Stars in the Computer . astronews.com, April 11, 2011
19. ↑ ^{a b} Deadly astronomical event not likely to happen in our galaxy, Study finds . ( Memento of the original from September 8, 2008 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. 
20. ↑ Did star explosion cause mass extinction?
21. ↑ Did a gamma-ray burst initiate the late Ordovician mass extinction? arxiv : astro-ph / 0309415
22. ↑ NASA's Swift Catches Farthest Ever Gamma-Ray Burst . NASA, September 13, 2008
23. ^ Gamma-ray bursts Coordinates Network . NASA
24. ^ New Gamma-Ray Burst Smashes Cosmic Distance Record . NASA
25. ^ Gamma-ray bursts Coordinates Network . NASA
26. ↑ Interview with Jochen Greiner about the observation of the most distant gamma-ray flash (MPG), April 30, 2009
27. ↑ Cosmic mega-event - Radiation flash blinds the NASA satellite . Spiegel Online , July 16, 2010
28. ↑ GRB 110328A-Chandra Observes Extraordinary Event harvard.edu, accessed May 3, 2011.
29. ↑ The GRB 110328A Symphony Astronomy Picture of the Day , April 19, 2011; GRB 110328A en.wikipedia
30. ↑ Cosmic gamma lightning sets new record scinexx.de
31. ↑ NASA's Fermi, Swift See 'Shockingly Bright' Burst nasa.gov; Brilliant GRB Blast with an Amateur Twist skyandtelescope.com, accessed December 29, 2017;
32. ↑ Gamma ray flashes: Cosmic event breaks energy record . SPIEGEL Online , November 22, 2013.
33. ↑ Mighty Gamma-Ray Flash: The Secret of GRB 130603B . Spiegel Online , August 4, 2013