GRB 020813
Encyclopedia
GRB 020813 was a gamma-ray burst (GRB) that was detected on 13 August 2002 at 02:44 UTC. A gamma-ray burst is a highly luminous
Luminosity
Luminosity is a measurement of brightness.-In photometry and color imaging:In photometry, luminosity is sometimes incorrectly used to refer to luminance, which is the density of luminous intensity in a given direction. The SI unit for luminance is candela per square metre.The luminosity function...

 flash associated with an explosion in a distant galaxy and producing gamma ray
Gamma ray
Gamma radiation, also known as gamma rays or hyphenated as gamma-rays and denoted as γ, is electromagnetic radiation of high frequency . Gamma rays are usually naturally produced on Earth by decay of high energy states in atomic nuclei...

s, the most energetic form of electromagnetic radiation
Electromagnetic radiation
Electromagnetic radiation is a form of energy that exhibits wave-like behavior as it travels through space...

, and often followed by a longer-lived "afterglow" emitted at longer wavelengths (X-ray
X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...

, ultraviolet
Ultraviolet
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...

, optical, infrared
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...

, and radio
Radio waves
Radio waves are a type of electromagnetic radiation with wavelengths in the electromagnetic spectrum longer than infrared light. Radio waves have frequencies from 300 GHz to as low as 3 kHz, and corresponding wavelengths from 1 millimeter to 100 kilometers. Like all other electromagnetic waves,...

).

Observations

GRB 020813 was detected on 13 August 2002 02:44 UTC by multiple instruments on the High Energy Transient Explorer
High Energy Transient Explorer
The High Energy Transient Explorer was an American astronomical satellite with international participation . The prime objective of HETE was to carry out the first multiwavelength study of gamma-ray bursts with UV, X-ray, and gamma-ray instruments mounted on a single, compact spacecraft...

. The burst lasted approximately 125 seconds. The initial position was estimated to be at a right ascension
Right ascension
Right ascension is the astronomical term for one of the two coordinates of a point on the celestial sphere when using the equatorial coordinate system. The other coordinate is the declination.-Explanation:...

 of and a declination
Declination
In astronomy, declination is one of the two coordinates of the equatorial coordinate system, the other being either right ascension or hour angle. Declination in astronomy is comparable to geographic latitude, but projected onto the celestial sphere. Declination is measured in degrees north and...

 of . In less than two hours after the burst had been detected, optical observations of the region were made with the Katzman Automatic Imaging Telescope
Katzman Automatic Imaging Telescope
The Katzman Automatic Imaging Telescope is an automated telescope used in the search for supernovae.The KAIT is a computer-controlled reflecting telescope with a 76 cm mirror and a CCD camera to take pictures. It is located at the Lick Observatory near San Jose, California.KAIT can take close to...

 which reveal the burst's optical afterglow. In the days following the event, observations were made by the Chandra X-ray Observatory
Chandra X-ray Observatory
The Chandra X-ray Observatory is a satellite launched on STS-93 by NASA on July 23, 1999. It was named in honor of Indian-American physicist Subrahmanyan Chandrasekhar who is known for determining the maximum mass for white dwarfs. "Chandra" also means "moon" or "luminous" in Sanskrit.Chandra...

, which detected a fading X-ray afterglow. The redshift
Redshift
In physics , redshift happens when light seen coming from an object is proportionally increased in wavelength, or shifted to the red end of the spectrum...

 for this event was approximately z = 1.254.

Supernova relation

Previous to this burst, there had not yet been any concrete evidence linking gamma-ray bursts to supernova
Supernova
A supernova is a stellar explosion that is more energetic than a nova. It is pronounced with the plural supernovae or supernovas. Supernovae are extremely luminous and cause a burst of radiation that often briefly outshines an entire galaxy, before fading from view over several weeks or months...

e, though it had long been hypothesized that the two phenomena were results of the same type of event. The spectrum of GRB 011211
GRB 011211
GRB 011211 was a gamma-ray burst detected on December 11, 2001. 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...

 was reported to include emission lines associated with the chemical element
Chemical element
A chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. Familiar examples of elements include carbon, oxygen, aluminum, iron, copper, gold, mercury, and lead.As of November 2011, 118 elements...

s magnesium, silicon, sulphur, argon, and calcium, which supported the theory that gamma-ray bursts are preceded by highly massive stars undergoing a supernova
Supernova
A supernova is a stellar explosion that is more energetic than a nova. It is pronounced with the plural supernovae or supernovas. Supernovae are extremely luminous and cause a burst of radiation that often briefly outshines an entire galaxy, before fading from view over several weeks or months...

 collapse. However, these results were considered statistically insignificant and somewhat controversial due to the low resolution of the instruments used. The spectrum of GRB 020813 was also found to display emission lines of elements associated with supernovae, in this case sulphur and silicon
Silicon
Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...

. This evidence confirmed the connection between supernovae and gamma-ray bursts.
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