Gamma-ray burst in the context of "High-energy astronomy"

Gamma-ray astronomy is a subfield of astronomy where scientists observe and study celestial objects and phenomena in outer space which emit cosmic electromagnetic radiation in the form of gamma rays, i.e. photons with the highest energies (above 100 keV) at the very shortest wavelengths. X-ray astronomy uses the next lower energy range, X-ray radiation, with energy below 100 keV.

In most cases, gamma rays from solar flares and Earth's atmosphere fall in the MeV range, but it's now known that solar flares can also produce gamma rays in the GeV range, contrary to previous beliefs. Much of the detected gamma radiation stems from collisions between hydrogen gas and cosmic rays within our galaxy. These gamma rays, originating from diverse mechanisms such as electron-positron annihilation, the inverse Compton effect and in some cases gamma decay, occur in regions of extreme temperature, density, and magnetic fields, reflecting violent astrophysical processes like the decay of neutral pions. They provide insights into extreme events like supernovae, hypernovae, and the behavior of matter in environments such as pulsars and blazars. A huge number of gamma ray emitting high-energy systems like black holes, stellar coronas, neutron stars, white dwarf stars, remnants of supernova, clusters of galaxies, including the Crab Nebula and the Vela Pulsar (the most powerful source so far), have been identified, alongside an overall diffuse gamma-ray background along the plane of the Milky Way galaxy. Cosmic radiation with the highest energy triggers electron-photon cascades in the atmosphere, while lower-energy gamma rays are only detectable above it. Gamma-ray bursts, like GRB 190114C, are transient phenomena challenging our understanding of high-energy astrophysical processes, ranging from microseconds to several hundred seconds.

In physics, relativistic beaming (also known as Doppler beaming, Doppler boosting, or the headlight effect) is the process by which relativistic effects modify the apparent luminosity of emitting matter that is moving at speeds close to the speed of light. In an astronomical context, relativistic beaming commonly occurs in two oppositely-directed relativistic jets of plasma that originate from a central compact object that is accreting matter. Accreting compact objects and relativistic jets are invoked to explain x-ray binaries, gamma-ray bursts, and, on a much larger scale, (AGN) active galactic nuclei (of which quasars are a particular variety).

Beaming affects the apparent brightness of a moving object. Consider a cloud of gas moving relative to the observer and emitting electromagnetic radiation. If the gas is moving towards the observer, it will be brighter than if it were at rest, but if the gas is moving away, it will appear fainter. The magnitude of the effect is illustrated by the AGN jets of the galaxies M87 and 3C 31 (see images at right). M87 has twin jets aimed almost directly towards and away from Earth; the jet moving towards Earth is clearly visible (the long, thin blueish feature in the top image at right), while the other jet is so much fainter it is not visible. In 3C 31, both jets (labeled in the lower figure at right) are at roughly right angles to our line of sight, and thus, both are visible. The upper jet points slightly more in Earth's direction and is therefore brighter.

The Hercules–Corona Borealis Great Wall (HCB) or simply the Great Wall is a putative galaxy filament that, if confirmed, would be the largest known structure in the observable universe, measuring approximately 10 billion light-years in length (the observable universe is about 93 billion light-years in diameter). This massive superstructure is a region of the sky seen in the data set mapping of gamma-ray bursts (GRBs) that has been found to have a concentration of similarly distanced GRBs that is unusually higher than the expected average distribution. It was discovered in early November 2013 by a team of American and Hungarian astronomers led by István Horváth, Jon Hakkila and Zsolt Bagoly while analyzing data from the Swift Gamma-Ray Burst Mission, together with other data from ground-based telescopes. If confirmed, it would be the largest known formation in the universe, exceeding the size of the Huge-LQG by about a factor of two.

The overdensity lies at the Second, Third and Fourth Galactic Quadrants (NGQ2, NGQ3 and NGQ4) of the sky. Thus, it lies in the Northern Hemisphere, centered on the border of the constellations Draco and Hercules. The entire clustering consists of around 19 GRBs with the redshift ranges between 1.6 and 2.1.

The Fermi Gamma-ray Space Telescope (FGST, also FGRST), formerly called the Gamma-ray Large Area Space Telescope (GLAST), is a space observatory being used to perform gamma-ray astronomy observations from low Earth orbit. Its main instrument is the Large Area Telescope (LAT), with which astronomers mostly intend to perform an all-sky survey studying astrophysical and cosmological phenomena such as active galactic nuclei, pulsars, other high-energy sources and dark matter. Another instrument aboard Fermi, the Gamma-ray Burst Monitor (GBM; formerly GLAST Burst Monitor), is being used to study gamma-ray bursts and solar flares.

Fermi, named for high-energy physics pioneer Enrico Fermi, was launched on 11 June 2008 at 16:05 UTC aboard a Delta II 7920-H rocket. The mission is a joint venture of NASA, the United States Department of Energy, and government agencies in France, Germany, Italy, Japan, and Sweden, becoming the most sensitive gamma-ray telescope on orbit, succeeding INTEGRAL. The project is a recognized CERN experiment (RE7).

GRB 190114C was an extreme gamma-ray burst explosion from a galaxy 4.5 billion light years away (z=0.4245; magnitude=15.60est) near the Fornax constellation, that was initially detected in January 2019. The afterglow light emitted soon after the burst was found to be tera-electron volt radiation from inverse Compton emission, identified for the first time. According to the astronomers, "We observed a huge range of frequencies in the electromagnetic radiation afterglow of GRB 190114C. It is the most extensive to date for a gamma-ray burst." Also, according to other astronomers, "light detected from the object had the highest energy ever observed for a GRB: 1 Tera electron volt (TeV)—about one trillion times as much energy per photon as visible light"; another source stated, "the brightest light ever seen from Earth [to date]."

GRB 030329 was a gamma-ray burst (GRB) that was detected on 29 March 2003 at 11:37 UTC. A gamma-ray burst is a highly luminous flash associated with an explosion in a distant galaxy and producing gamma rays, the most energetic form of electromagnetic radiation, and often followed by a longer-lived "afterglow" emitted at longer wavelengths (X-ray, ultraviolet, optical, infrared, and radio). GRB 030329 was the first burst whose afterglow definitively exhibited characteristics of a supernova, confirming the existence of a relationship between the two phenomena.

Orbital decay is a gradual decrease of the distance between two orbiting bodies at their closest approach (the periapsis) over many orbital periods. These orbiting bodies can be a planet and its satellite, a star and any object orbiting it, or components of any binary system. If left unchecked, the decay eventually results in termination of the orbit when the smaller object strikes the surface of the primary; or for objects where the primary has an atmosphere, the smaller object burns, explodes, or otherwise breaks up in the larger object's atmosphere; or for objects where the primary is a star, ends with incineration by the star's radiation (such as for comets). Collisions of stellar-mass objects are usually accompanied by effects such as gamma-ray bursts and detectable gravitational waves.

Orbital decay is caused by one or more mechanisms which absorb energy from the orbital motion, such as fluid friction, gravitational anomalies, or electromagnetic effects. For bodies in low Earth orbit, the most significant effect is atmospheric drag.