Gamma-ray astronomy is the astronomical study of the cosmos with gamma rays. Astronomy (from the Greek words astron (ἄστρον "star" and nomos (νόμος "law" is the scientific study In its most general sense a cosmos is an orderly or harmonious system Gamma rays (denoted as &gamma) are a form of Electromagnetic radiation or light emission of frequencies produced by sub-atomic particle interactions
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Early history
Long before experiments could detect gamma rays emitted by cosmic sources, scientists had known that the universe should be producing these photons. Gamma rays (denoted as &gamma) are a form of Electromagnetic radiation or light emission of frequencies produced by sub-atomic particle interactions In Physics, the photon is the Elementary particle responsible for electromagnetic phenomena Work by Eugene Feenberg and H. Eugene Feenberg ( October 6, 1906 in Fort Smith Texas &ndash November 7, 1977) was an American physicist who made contributions to Primakoff in 1948, Sachio Hayakawa and I. B. Hutchinson in 1952, and, especially, Morrison in 1958 had led scientists to believe that a number of different processes which were occurring in the universe would result in gamma-ray emission. These processes included cosmic ray interactions with interstellar gas, supernova explosions, and interactions of energetic electrons with magnetic fields. For the 1962 Bruce Conner film see Cosmic Ray (film Cosmic rays are energetic particles originating from space that impinge on A supernova (plural supernovae or supernovas) is a stellar Explosion. The electron is a fundamental Subatomic particle that was identified and assigned the negative charge in 1897 by J In Physics, a magnetic field is a Vector field that permeates space and which can exert a magnetic force on moving Electric charges However, it was not until the 1960s that our ability to actually detect these emissions came to pass. The 1960s decade refers to the years from the beginning of 1960 to the end of 1969
Gamma-rays coming from space are mostly absorbed by the Earth's atmosphere. So gamma-ray astronomy could not develop until it was possible to get our detectors above all or most of the atmosphere, using balloons or spacecraft. A balloon is a flexible bag filled with a type of Gas, such as Helium, Hydrogen, Nitrous oxide or air. The first gamma-ray telescope carried into orbit, on the Explorer 11 satellite in 1961, picked up fewer than 100 cosmic gamma-ray photons. Explorer 11 (also known as S15 was the orbital spacecraft that carried the first Gamma ray Telescope. These appeared to come from all directions in the Universe, implying some sort of uniform "gamma-ray background". Such a background would be expected from the interaction of cosmic rays (very energetic charged particles in space) with gas found between the stars.
The first true astrophysical gamma-ray sources were solar flares, which revealed the strong 2. 223 MeV line predicted by Morrison. This line results from the formation of deuterium via the union of a neutron and proton; in a solar flare the neutrons appear as secondaries from interactions of high-energy ions accelerated in the flare process. These first gamma-ray line observations were from OSO-3, OSO-7, and the Solar Maximum Mission, the latter spacecraft launched in 1980. The Solar Maximum Mission Satellite (or SolarMax was designed to investigate solar phenomenon particularly Solar flares. The solar observations inspired theoretical work by Reuven Ramaty and others. Reuven Ramaty (1937 - 2001 was a pioneer in the fields of Solar physics, Gamma-ray astronomy, Nuclear astrophysics, and Cosmic rays.
Significant gamma-ray emission from our galaxy was first detected in 1967 by the gamma-ray detector aboard the OSO-3 satellite. It detected 621 events attributable to cosmic gamma-rays. However, the field of gamma-ray astronomy took great leaps forward with the SAS-2 (1972) and the COS-B (1975-1982) satellites. The Second Small Astronomy Satellite, also known also as SAS-2, SAS B or Explorer 48, was a NASA Gamma ray telescope. Cos-B was the first European Space Agency mission to study gamma-ray sources These two satellites provided an exciting view into the high-energy universe (sometimes called the 'violent' universe, because the kinds of events in space that produce gamma-rays tend to be explosions, high-speed collisions, and such). They confirmed the earlier findings of the gamma-ray background, produced the first detailed map of the sky at gamma-ray wavelengths, and detected a number of point sources. However, the poor resolution of the instruments made it impossible to identify most of these point sources with individual stars or stellar systems.
Early discoveries
Perhaps the most spectacular discovery in gamma-ray astronomy came in the late 1960s and early 1970s from a constellation of defense satellites which were put into orbit for a completely different reason. Detectors on board the Vela satellite series, designed to detect flashes of gamma-rays from nuclear bomb blasts, began to record bursts of gamma-rays -- not from the vicinity of the Earth, but from deep space! Today, these gamma-ray bursts are seen to last for fractions of a second to minutes, popping off like cosmic flashbulbs from unexpected directions, flickering, and then fading after briefly dominating the gamma-ray sky. Vela was the name of a group of Satellites developed as the Vela Hotel element of Project Vela by the United States to monitor compliance with Gamma-ray bursts ( GRB s are the most luminous electromagnetic events occurring in the Universe since the Big Bang. Studied for over 25 years now with instruments on board a variety of satellites and space probes, including Soviet Venera spacecraft and the Pioneer Venus Orbiter, the sources of these enigmatic high-energy flashes remain a mystery. The Venera (Венера series of probes was developed by the USSR between 1961 and 1984 to gather data from Venus. The Pioneer mission to Venus consisted of two components launched separately They appear to come from far away in the Universe, and currently the most likely theory seems to be that at least some of them come from so-called hypernova explosions - supernovas creating black holes rather than neutron stars. Hypernova (pl hypernovae) refers to an exceptionally large Star that collapses at the end of its lifespan—for example a collapsar, or a large A black hole is a theoretical region of space in which the Gravitational field is so powerful that nothing not even Electromagnetic radiation (e A neutron star is a type of remnant that can result from the Gravitational collapse of a massive Star during a Type II, Type Ib or Type
Recent and current observatories
During its High Energy Astrophysics Observatory program in 1977, NASA announced plans to build a "great observatory" for gamma-ray astronomy. Also 1977 (album by Ash. Year 1977 ( MCMLXXVII) was a Common year starting on Saturday (link displays The National Aeronautics and Space Administration ( NASA, ˈnæsə is an agency of the United States government, responsible for the nation's public space program The Compton Gamma-Ray Observatory (CGRO) was designed to take advantage of the major advances in detector technology during the 1980s, and was launched in 1991. The satellite carried four major instruments which have greatly improved the spatial and temporal resolution of gamma-ray observations. The CGRO provided large amounts of data which are being used to improve our understanding of the high-energy processes in our Universe. CGRO was de-orbited in June 2000 as a result of the failure of one of its stabilizing gyroscopes. A gyroscope is a device for measuring or maintaining orientation, based on the principles of Angular momentum.
BeppoSAX was launched in 1996 and deorbited in 2003. BeppoSAX was an Italian - Dutch Satellite for X-ray astronomy. Predominantly X-rays but also studied gamma-ray bursts.
The High Energy Transient Explorer 2 (HETE-2) was launched in October 2000 (on a nominally 2 yr mission) and was still operational in March 2007. The High Energy Transient Explorer (abbreviated HETE; also known as Explorer 79 is an American astronomical satellite with international participation (mainly Japan
Swift a NASA spacecraft was launched in 2004 and carries the BAT instrument. The Swift Gamma-Ray Burst Mission consists of a Robotic spacecraft called Swift, which was launched into Orbit on November 20, 2004
Currently, the main space-based gamma ray observatory is the INTErnational Gamma-Ray Astrophysics Laboratory, (INTEGRAL). The European Space Agency 's INTErnational Gamma-Ray Astrophysics Laboratory ( INTEGRAL) is detecting some of the most energetic radiation that comes from space INTEGRAL is an ESA mission with contributions from Czech, Poland, USA and Russia. It was launched on 17 October 2002. Events 539 BC - King Cyrus The Great of Persia marches into the city of Babylon, releasing the Jews from almost See also 2002 (disambiguation Year 2002 ( MMII) was a Common year starting on Tuesday of the Gregorian calendar.
Very energetic gamma-rays can also be detected by ground based experiments. The Imaging Atmospheric Cherenkov Telescope technique currently achieves the highest sensitivity. The Crab Nebula, a steady source of so called TeV gamma-rays was first detected in 1989 by the Whipple Observatory (Az, USA). Modern Cherenkov telescope experiments like H.E.S.S., VERITAS, MAGIC, and CANGAROO III can detect the Crab Nebula in a few minutes. HESS-dark-fulljpg|thumb|All four telescopes in operation at night]] High Energy Stereoscopic System or H In Roman mythology, Veritas (meaning truth) was the Goddess of Truth, a daughter of Saturn and the mother of Virtue. MAGIC ( Major Atmospheric Gamma-ray Imaging Cherenkov Telescope) is a Gamma-ray telescope situated at the Roque de los Muchachos Observatory on La Palma The most energetic photons (up to 16 TeV) observed from an extragalactic object originate from the blazar Markarian 501 (Mrk 501). A blazar is a very compact and highly variable energy source associated with a presumed Supermassive black hole at the center of a Host galaxy. These measurements were done by the High-Energy-Gamma-Ray Astronomy (HEGRA) air Cherenkov telescopes. This article is about the Physics experiment. For other meanings see Hegra (disambiguation HEGRA, which stands for High-Energy-Gamma-Ray Čerenkov radiation (also spelled Cerenkov or Cherenkov) is Electromagnetic radiation emitted when a charged particle (such as an
Gamma-ray astronomy is mostly dominated by the number of photons that can be detected. Larger area detectors and better background suppression are essential for progress in the field.
Future GR observatories
NASA plans to launch GLAST (with LAT and BM) in 2008.
See also
- Gamma-ray telescopes
- X-ray astronomy
External links
- The HEGRA Atmospheric Cherenkov Telescope System
- The HESS Ground Based Gamma-Ray Experiment
- The MAGIC Telescope Project
- The VERITAS Ground Based Gamma-Ray Experiment
- The space-borne INTEGRAL observatory
- NASA's Swift gamma-ray burst mission
- The CACTUS Ground Based Air Cherenkov Telescope
- TACTIC(TeV Gamma-Ray Telescope)
- NASA HETE-2 satellite
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