Editing Gamma-ray burst (section)

== History ==
{{Main|History of gamma-ray burst research}}
[[File:BATSE 2704.jpg|thumb|Positions on the sky of all gamma-ray bursts detected during the BATSE mission. The distribution is [[isotropic]], with no concentration towards the plane of the Milky Way, which runs horizontally through the center of the image.]]Gamma-ray bursts were first observed in the late 1960s by the U.S. [[Vela (satellite)|Vela]] satellites, which were built to detect gamma radiation pulses emitted by nuclear weapons tested in space. The [[United States]] suspected that the [[Soviet Union]] might attempt to conduct secret nuclear tests after signing the [[Nuclear Test Ban Treaty]] in 1963.<ref>{{cite journal | title = A brief history of the discovery of cosmic gamma-ray bursts | last1 = Bonnell | first1 = JT | last2 = Klebesadel | first2 = RW | date = 1996 | journal = AIP Conference Proceedings | volume = 384 | issue = 1 | pages = 977–980 | doi = 10.1063/1.51630| bibcode = 1996AIPC..384..977B }}</ref> On July 2, 1967, at 14:19 [[UTC]], the Vela 4 and Vela 3 satellites detected a flash of gamma radiation unlike any known nuclear weapons signature.<ref name="FlashVela" /> Uncertain what had happened but not considering the matter particularly urgent, the team at the [[Los Alamos National Laboratory]], led by [[Ray Klebesadel]], filed the data away for investigation. As additional Vela satellites were launched with better instruments, the Los Alamos team continued to find inexplicable gamma-ray bursts in their data. By analyzing the different arrival times of the bursts as detected by different satellites, the team was able to determine rough estimates for the [[Star position|sky positions]] of 16 bursts<ref name="FlashVela">[[#Schilling|Schilling 2002]], pp. 12–16</ref><ref>{{Cite journal |last1=Klebesadel |first1=R. W. |last2=et |first2=al |date=1973 |title=Observations of Gamma-Ray Bursts of Cosmic Origin |url=https://adsabs.harvard.edu/full/1973ApJ...182L..85K |journal=Astrophysical Journal |volume=182 |pages=85|doi=10.1086/181225 |bibcode=1973ApJ...182L..85K }}</ref> and definitively rule out a terrestrial or solar origin. Contrary to popular belief, the data was never classified.<ref name="BK">{{cite journal |last1=Bonnell |first1=J. T. |last2=Klebesadel |first2=R. W. |title=A brief history of the discovery of cosmic gamma-ray bursts |journal=AIP Conference Proceedings |date=1996 |volume=384 |page=979 |doi=10.1063/1.51630 |bibcode=1996AIPC..384..977B }}</ref> After thorough analysis, the findings were published in 1973 as an ''[[Astrophysical Journal]]'' article entitled "Observations of Gamma-Ray Bursts of Cosmic Origin".<ref name="KSO">{{cite journal|bibcode=1973ApJ...182L..85K |title=Observations of Gamma-Ray Bursts of Cosmic Origin |author1=Klebesadel R.W. |author2=Strong I.B. |author3=Olson R.A. |date=1973 |journal=Astrophysical Journal Letters |volume=182 |page=L85 |doi=10.1086/181225}}</ref>

Most early hypotheses of gamma-ray bursts posited nearby sources within the [[Milky Way Galaxy]]. From 1991, the [[Compton Gamma Ray Observatory]] (CGRO) and its Burst and Transient Source Explorer ([[CGRO#Instruments|BATSE]]) instrument, an extremely sensitive gamma-ray detector, provided data that showed the distribution of GRBs is [[Isotropy|isotropic]] (that is, not biased towards any particular direction in space).<ref>[[#Meegan|Meegan 1992]]</ref> If the sources were from within our own galaxy, they would be strongly concentrated in or near the galactic plane. The absence of any such pattern in the case of GRBs provided strong evidence that gamma-ray bursts must come from beyond the Milky Way.<ref name="Vedrenne p. 16–40">[[#VedrenneAtteia|Vedrenne & Atteia 2009]], pp. 16–40</ref><ref>[[#Schilling|Schilling 2002]], pp. 36–37</ref><ref>[[#Pac95|Paczyński 1999]], p. 6</ref><ref name="Piran92">[[#Piran92|Piran 1992]]</ref> However, some Milky Way models are still consistent with an isotropic distribution.<ref name="Vedrenne p. 16–40" /><ref name="Lamb">[[#Lamb|Lamb 1995]]</ref>

=== Counterpart objects as candidate sources ===
For decades after the discovery of GRBs, astronomers searched for a counterpart at other wavelengths: i.e., any astronomical object in positional coincidence with a recently observed burst. Astronomers considered many distinct classes of objects, including [[white dwarf]]s, [[pulsar]]s, [[supernova]]e, [[globular cluster]]s, [[quasar]]s, [[Seyfert galaxy|Seyfert galaxies]], and [[BL Lac object]]s.<ref name="spatial">[[#HurleyConf|Hurley 1986]], p. 33</ref> All such searches were unsuccessful,<ref group="nb" name="790305b">A notable exception is the [[GRB 790305b|5 March event]] of 1979, an extremely bright burst that was successfully localized to supernova remnant [[LMC N49|N49]] in the [[Large Magellanic Cloud]]. This event is now interpreted as a [[magnetar]] [[Gamma-ray burst progenitors#Magnetar giant flares|giant flare]], more related to [[soft gamma repeater|SGR]] flares than "true" gamma-ray bursts.</ref> and in a few cases particularly well-localized bursts (those whose positions were determined with what was then a high degree of accuracy) could be clearly shown to have no bright objects of any nature consistent with the position derived from the detecting satellites. This suggested an origin of either very faint stars or extremely distant galaxies.<ref>[[#Pedersen|Pedersen 1987]]</ref><ref>[[#Hurley92|Hurley 1992]]</ref> Even the most accurate positions contained numerous faint stars and galaxies, and it was widely agreed that final resolution of the origins of cosmic gamma-ray bursts would require both new satellites and faster communication.<ref name="CFishman" />

=== Afterglow ===
[[File:BeppoSAX.jpg|thumb|The Italian–Dutch satellite [[BeppoSAX]], launched in April 1996, provided the first accurate positions of gamma-ray bursts, allowing follow-up observations and identification of the sources.]]Several models for the origin of gamma-ray bursts postulated that the initial burst of gamma rays should be followed by ''afterglow'': slowly fading emission at longer wavelengths created by collisions between the burst [[ejecta]] and interstellar gas.<ref>[[#Pac93|Paczynski 1993]]</ref> Early searches for this afterglow were unsuccessful, largely because it is difficult to observe a burst's position at longer wavelengths immediately after the initial burst. The breakthrough came in February 1997 when the satellite [[BeppoSAX]] detected a gamma-ray burst ([[GRB 970228]]<ref group="nb" name="grbnames">GRBs are named after the date on which they are discovered: the first two digits being the year, followed by the two-digit month and two-digit day and a letter with the order they were detected during that day. The letter 'A' is appended to the name for the first burst identified, 'B' for the second, and so on. For bursts before the year 2010, this letter was only appended if more than one burst occurred that day.</ref>) and when the X-ray camera was pointed towards the direction from which the burst had originated, it detected fading X-ray emission. The [[William Herschel Telescope]] identified a fading optical counterpart 20 hours after the burst.<ref>[[#Paradijs|van Paradijs 1997]]</ref> Once the GRB faded, deep imaging was able to identify a faint, distant host galaxy at the location of the GRB as pinpointed by the optical afterglow.<ref name="Vedrenne p. 90">[[#VedrenneAtteia|Vedrenne & Atteia 2009]], pp. 90–93</ref><ref>[[#Schilling|Schilling 2002]], p. 102</ref>

Because of the very faint luminosity of this galaxy, its exact distance was not measured for several years. Well after then, another major breakthrough occurred with the next event registered by BeppoSAX, [[GRB 970508]]. This event was localized within four hours of its discovery, allowing research teams to begin making observations much sooner than any previous burst. The [[absorption spectrum|spectrum]] of the object revealed a [[redshift]] of ''z''&nbsp;=&nbsp;0.835, placing the burst at a distance of roughly 6&nbsp;billion&nbsp;[[light year]]s from Earth.<ref>[[#Reichart|Reichart 1995]]</ref> This was the first accurate determination of the distance to a GRB, and together with the discovery of the host galaxy of 970228 proved that GRBs occur in extremely distant galaxies.<ref name="Vedrenne p. 90" /><ref>[[#Schilling|Schilling 2002]], pp. 118–123</ref> Within a few months, the controversy about the distance scale ended: GRBs were extragalactic events originating within faint galaxies at enormous distances. The following year, [[GRB 980425]] was followed within a day by a bright supernova ([[SN 1998bw]]), coincident in location, indicating a clear connection between GRBs and the deaths of very massive stars. This burst provided the first strong clue about the nature of the systems that produce GRBs.<ref name="98bw">[[#Galama|Galama 1998]]</ref>

=== More recent instruments – launched from 2000 ===
[[File:Swift spacecraft.jpg|thumb|left|[[NASA]]'s [[Swift Gamma-Ray Burst Mission|Swift Spacecraft]] launched in November 2004]]
BeppoSAX functioned until 2002 and [[Compton Gamma Ray Observatory|CGRO]] (with BATSE) was deorbited in 2000. However, the revolution in the study of gamma-ray bursts motivated the development of a number of additional instruments designed specifically to explore the nature of GRBs, especially in the earliest moments following the explosion. The first such mission, [[High Energy Transient Explorer|HETE-2]],<ref>[[#HETE|Ricker 2003]]</ref> was launched in 2000 and functioned until 2006, providing most of the major discoveries during this period. One of the most successful space missions to date, [[Swift Gamma-Ray Burst Mission|Swift]], was launched in 2004 and as of May 2024 is still operational.<ref>[[#NASA2008|McCray 2008]]</ref><ref>[[#Gehrels04|Gehrels 2004]]</ref> Swift is equipped with a very sensitive gamma-ray detector as well as on-board X-ray and optical telescopes, which can be rapidly and automatically [[Slew (spacecraft)|slewed]] to observe afterglow emission following a burst. More recently, the [[Fermi Gamma-ray Space Telescope|Fermi]] mission was launched carrying the [[Fermi Gamma-ray Burst Monitor|Gamma-Ray Burst Monitor]], which detects bursts at a rate of several hundred per year, some of which are bright enough to be observed at extremely high energies with Fermi's [[Fermi LAT|Large Area Telescope]]. Meanwhile, on the ground, numerous optical telescopes have been built or modified to incorporate robotic control software that responds immediately to signals sent through the [[Gamma-ray Burst Coordinates Network]]. This allows the telescopes to rapidly repoint towards a GRB, often within seconds of receiving the signal and while the gamma-ray emission itself is still ongoing.<ref>[[#ROTSE|Akerlof 2003]]</ref><ref>[[#Akerlof99|Akerlof 1999]]</ref>

The [[Space Variable Objects Monitor]] is a small [[X-ray telescope]] satellite for studying the explosions of massive stars by analysing the resulting gamma-ray bursts, developed by [[China National Space Administration]] (CNSA), [[Chinese Academy of Sciences]] (CAS) and the French Space Agency ([[CNES]]),<ref name="Leicester">{{cite web|url=https://www2.le.ac.uk/offices/press/press-releases/2015/october/lobster-inspired-ps3-8m-super-lightweight-mirror-chosen-for-chinese-french-space-mission|title=Lobster-inspired £3.8m super lightweight mirror chosen for Chinese-French space mission|publisher=University of Leicester|date=26 October 2015|access-date=20 May 2021 |url-status=dead |archive-url=https://web.archive.org/web/20210128093757/https://www2.le.ac.uk/offices/press/press-releases/2015/october/lobster-inspired-ps3-8m-super-lightweight-mirror-chosen-for-chinese-french-space-mission |archive-date=28 Jan 2021 }}</ref> launched on 22 June 2024 (07:00:00 UTC).

The [[Taiwan Space Agency]] is launching a [[CubeSat|cubesat]] called [[The Gamma-ray Transients Monitor]] to track GRBs and other bright gamma-ray transients with energies ranging from 50 keV to 2 MeV in Q4 2026.<ref>{{Cite journal |last1=Chang |first1=Hsiang-Kuang |last2=Lin |first2=Chi-Hsun |last3=Tsao |first3=Che-Chih |last4=Chu |first4=Che-Yen |last5=Yang |first5=Shun-Chia |last6=Huang |first6=Chien-You |last7=Wang |first7=Chao-Hsi |last8=Su |first8=Tze-Hsiang |last9=Chung |first9=Yun-Hsin |last10=Chang |first10=Yung-Wei |last11=Gong |first11=Zi-Jun |last12=Hsiang |first12=Jr-Yue |last13=Lai |first13=Keng-Li |last14=Lin |first14=Tsu-Hsuan |last15=Lu |first15=Chia-Yu |date=2022-01-15 |title=The Gamma-ray Transients Monitor (GTM) on board Formosat-8B and its GRB detection efficiency |journal=Advances in Space Research |volume=69 |issue=2 |pages=1249–1255 |doi=10.1016/j.asr.2021.10.044 |bibcode=2022AdSpR..69.1249C |issn=0273-1177|doi-access=free }}</ref>

===Short bursts and other observations===
New developments since the 2000s include the recognition of short gamma-ray bursts as a separate class (likely from merging neutron stars and not associated with supernovae), the discovery of extended, erratic flaring activity at X-ray wavelengths lasting for many minutes after most GRBs, and the discovery of the most luminous {{nowrap|([[GRB 080319B]])}} and the former most distant {{nowrap|([[GRB 090423]])}} emissive sources in the universe.<ref name="Bloom">[[#Bloom|Bloom 2009]]</ref><ref>[[#090423|Reddy 2009]]</ref> Prior to a flurry of discoveries from the [[James Webb Space Telescope]], the presumptive source of {{nowrap|[[GRB 090429B]]}} was the most distant known object in the universe.

In October 2018, astronomers reported that {{nowrap|GRB 150101B}} (detected in 2015) and [[GW170817]], a [[gravitational wave]] event detected in 2017 (which has been associated with {{nowrap|GRB 170817A}}, a burst detected 1.7 seconds later), may have been produced by the same mechanism—the [[Neutron star merger|merger]] of two [[neutron star]]s. The similarities between the two events, in terms of [[gamma ray]], [[optical]], and [[x-ray]] emissions, as well as to the nature of the associated host [[Galaxy|galaxies]], were considered "striking", suggesting the two separate events may both be the result of the merger of neutron stars, and both may be a [[kilonova]], which may be more common in the universe than previously understood, according to the researchers.<ref name="EA-20181016">{{cite press release |author=University of Maryland |title=All in the family: Kin of gravitational wave source discovered – New observations suggest that kilonovae – immense cosmic explosions that produce silver, gold and platinum – may be more common than thought |url=https://www.eurekalert.org/pub_releases/2018-10/uom-ait101518.php |date=16 October 2018 |work=[[EurekAlert!]] |access-date=17 October 2018 |author-link=University of Maryland |archive-date=16 October 2018 |archive-url=https://web.archive.org/web/20181016142323/https://www.eurekalert.org/pub_releases/2018-10/uom-ait101518.php |url-status=dead }}</ref><ref name="NC-20181016">{{cite journal |author=Troja, E.|display-authors=etal |title=A luminous blue kilonova and an off-axis jet from a compact binary merger at z = 0.1341 |date=16 October 2018 |journal=[[Nature Communications]] |volume=9 |pages=4089 |number=4089 (2018) |doi=10.1038/s41467-018-06558-7 |pmid=30327476 |pmc=6191439 |arxiv=1806.10624 |bibcode=2018NatCo...9.4089T }}</ref><ref name="NASA-20181016">{{cite news |last=Mohon |first=Lee |title=GRB 150101B: A Distant Cousin to GW170817 |url=https://www.nasa.gov/mission_pages/chandra/images/grb-150101b-a-distant-cousin-to-gw170817.html |date=16 October 2018 |work=[[NASA]] |access-date=17 October 2018 }}</ref><ref name="SPC-20181017">{{cite web |last=Wall |first=Mike |title=Powerful Cosmic Flash Is Likely Another Neutron-Star Merger |url=https://www.space.com/42158-another-neutron-star-crash-detected.html |date=17 October 2018 |work=[[Space.com]] |access-date=17 October 2018 }}</ref>

The highest energy light observed from a gamma-ray burst was one [[Electronvolt|teraelectronvolt]], from {{nowrap|[[GRB 190114C]]}} in 2019.<ref name="NAT-20191120">{{cite journal |author=Veres, P |s2cid=208191199 |display-authors=et al. |title=Observation of inverse Compton emission from a long γ-ray burst |date=20 November 2019 |journal=[[Nature (journal)|Nature]] |volume=575 |issue=7783 |pages=459–463 |doi=10.1038/s41586-019-1754-6 |pmid=31748725 |arxiv=2006.07251 |bibcode=2019Natur.575..459M }}</ref> Although enormous for such a distant event, this energy is around 3 orders of magnitude lower than the highest energy light observed from closer gamma ray sources within our [[Milky Way]] galaxy, for example a 2021 event of 1.4 petaelectronvolts.<ref>{{Cite web |date=2021-05-21 |title=Record-breaking light has more than a quadrillion electron volts of energy |url=https://www.sciencenews.org/article/light-energy-record-gamma-ray |access-date=2022-05-11 |website=Science News |first=Emily |last=Conover |language=en-US}}</ref>