Editing Gamma-ray burst (section)

== Energetics ==
[[File:GRB080319B illustration NASA.jpg|thumb|Artist's illustration of a bright gamma-ray burst occurring in a star-forming region. Energy from the explosion is beamed into two narrow, oppositely directed jets.]]Gamma-ray bursts are very bright as observed from Earth despite their typically immense distances. An average long GRB has a [[bolometric magnitude|bolometric]] flux comparable to a bright star of our galaxy despite a distance of billions of light years (compared to a few tens of light years for most visible stars). Most of this energy is released in gamma rays, although some GRBs have extremely luminous optical counterparts as well. [[GRB 080319B]], for example, was accompanied by an optical counterpart that peaked at a [[visible magnitude]] of 5.8,<ref name="Racusin">[[#Racusin08|Racusin 2008]]</ref> comparable to that of the dimmest naked-eye stars despite the burst's distance of 7.5&nbsp;billion light years. This combination of brightness and distance implies an extremely energetic source. Assuming the gamma-ray explosion to be spherical, the energy output of GRB 080319B would be within a factor of two of the [[Mass–energy equivalence|rest-mass energy]] of the [[Sun]] (the energy which would be released were the Sun to be converted entirely into radiation).<ref name="Bloom" />

Gamma-ray bursts are thought to be highly focused explosions, with most of the explosion energy [[collimated light|collimated]] into a narrow [[relativistic jet|jet]].<ref>[[#Rykoff|Rykoff 2009]]</ref><ref>[[#Abdo|Abdo 2009]]</ref> The jets of gamma-ray bursts are [[Ultrarelativistic limit|ultrarelativistic]], and are the most relativistic jets in the universe.<ref>{{Cite journal |last1=Dereli-Bégué |first1=Hüsne |last2=Pe’er |first2=Asaf |last3=Ryde |first3=Felix |last4=Oates |first4=Samantha R. |last5=Zhang |first5=Bing |last6=Dainotti |first6=Maria G. |date=2022-09-24 |title=A wind environment and Lorentz factors of tens explain gamma-ray bursts X-ray plateau |journal=Nature Communications |language=en |volume=13 |issue=1 |pages=5611 |doi=10.1038/s41467-022-32881-1 |pmid=36153328 |pmc=9509382 |arxiv=2207.11066 |bibcode=2022NatCo..13.5611D |issn=2041-1723}}</ref><ref>{{Cite journal |last=Pe’er |first=Asaf |date=2019 |title=Plasmas in Gamma-Ray Bursts: Particle Acceleration, Magnetic Fields, Radiative Processes and Environments |journal=Galaxies |language=en |volume=7 |issue=1 |pages=33 |doi=10.3390/galaxies7010033 |arxiv=1902.02562 |bibcode=2019Galax...7...33P |issn=2075-4434 |doi-access=free }}</ref> The matter in gamma-ray burst jets may also become [[Faster-than-light|superluminal]], or faster than the speed of light in the jet medium, with there also being effects of [[time reversibility]].<ref>{{Cite journal |last1=Hakkila |first1=Jon |last2=Nemiroff |first2=Robert |date=2019-09-23 |title=Time-reversed Gamma-Ray Burst Light-curve Characteristics as Transitions between Subluminal and Superluminal Motion |journal=The Astrophysical Journal |language=en |volume=883 |issue=1 |pages=70 |doi=10.3847/1538-4357/ab3bdf |arxiv=1908.07306 |bibcode=2019ApJ...883...70H |issn=0004-637X |doi-access=free }}</ref><ref>{{Cite web |last=Ratner |first=Paul |date=2019-09-25 |title=Astrophysicists: Gamma-ray jets exceed the speed of light |url=https://bigthink.com/hard-science/astrophysicists-gamma-ray-jets-speed-of-light/ |access-date=2023-10-11 |website=Big Think |language=en-US}}</ref><ref>{{Cite web |last=Siegel |first=Ethan |author-link=Ethan Siegel |date=2019-10-05 |title=Ask Ethan: Can Gamma-Ray Jets Really Travel Faster Than The Speed Of Light? |url=https://www.forbes.com/sites/startswithabang/2019/10/05/ask-ethan-can-gamma-ray-jets-really-travel-faster-than-the-speed-of-light/ |access-date=2023-10-11 |website=Forbes |language=en}}</ref> The approximate angular width of the jet (that is, the degree of spread of the beam) can be estimated directly by observing the achromatic "jet breaks" in afterglow light curves: a time after which the slowly decaying afterglow begins to fade rapidly as the jet slows and can no longer [[relativistic beaming|beam]] its radiation as effectively.<ref name="Sari99">[[#Sari99|Sari 1999]]</ref><ref>[[#Burrows|Burrows 2006]]</ref> Observations suggest significant variation in the jet angle from between 2 and 20 degrees.<ref name="Frail">[[#Frail|Frail 2001]]</ref>

Because their energy is strongly focused, the gamma rays emitted by most bursts are expected to miss the Earth and never be detected. When a gamma-ray burst is pointed towards Earth, the focusing of its energy along a relatively narrow beam causes the burst to appear much brighter than it would have been were its energy emitted spherically. The total energy of typical gamma-ray bursts has been estimated at 3 × 10<sup>44</sup>&nbsp;J,{{snd}}which is larger than the total energy (10<sup>44</sup>&nbsp;J) of ordinary [[supernova]]e (type [[Type Ia supernova|Ia]], [[Type Ib and Ic supernovae|Ibc]], [[Type II supernova|II]]),<ref name="Frail" /> with gamma-ray bursts also being more [[Power (physics)|powerful]] than the typical supernova.<ref>{{Cite book |last=Melia |first=Fulvio |author-link=Fulvio Melia |title=High-Energy Astrophysics |publisher=Princeton University Press |year=2009 |isbn=978-0-691-13543-4 |pages=241 |language=en}}</ref> Very bright supernovae have been observed to accompany several of the nearest GRBs.<ref name="98bw" /> Further support for focusing of the output of GRBs comes from observations of strong asymmetries in the spectra of nearby [[Type Ib and Ic supernovae|type Ic supernovae]]<ref>[[#Mazzali|Mazzali 2005]]</ref> and from radio observations taken long after bursts when their jets are no longer relativistic.<ref>[[#Frail2000|Frail 2000]]</ref>

The discovery of [[GRB 190114C]] suggests that previous observations may have underestimated the total energy output of GRBs.<ref>{{Cite web |last=Billings |first=Lee |date=2019-11-20 |title=Record-Breaking Gamma Rays Reveal Secrets of the Universe's Most Powerful Explosions |url=https://www.scientificamerican.com/article/record-breaking-gamma-rays-reveal-secrets-of-the-universes-most-powerful-explosions/ |access-date=2023-09-17 |website=Scientific American |language=en}}</ref> Measurements indicate that the energy released in very-high-energy gamma rays may be comparable to the combined energy emitted at all lower wavelengths.<ref>{{Cite web |last=Choi |first=Charles Q. |date=2019-11-20 |title=The Most Powerful Explosions in the Universe Emit Way More Energy Than Anyone Thought |url=https://www.space.com/gamma-ray-bursts-high-energy-light.html |access-date=2023-09-17 |website=Space.com |language=en}}</ref>

Short (time duration) GRBs appear to come from a lower-redshift (i.e. less distant) population and are less luminous than long GRBs.<ref name="SHBhosts">[[#Prochaska|Prochaska 2006]]</ref> The degree of beaming in short bursts has not been accurately measured, but as a population they are likely less collimated than long GRBs<ref>[[#Watson|Watson 2006]]</ref> or possibly not collimated at all in some cases.<ref>[[#Grupe|Grupe 2006]]</ref>