Green Bank Interferometer
Encyclopedia
The Green Bank Interferometer (GBI) is a former radio astronomy
telescope
located at Green Bank
, West Virginia
(USA
) and operated by the National Radio Astronomy Observatory (NRAO). It included three radio telescopes of 85-foot (26m) diameter, designated 85-1, 85-3, and 85-2 (85-1 is also known as the Tatel Telescope).
The GBI began operation in 1964 as a two element interferometer in order to test large aperture synthesis
arrays and study radio astrometry
and interstellar scintillation
. In 1967 the array was upgraded with construction of the third element. From 1978-1996, it was operated in support of USNO and NRL
geodetic and astronomy programs, but then briefly suspended operations.
The Green Bank Interferometer (GBI) resumed operation as a radio monitoring instrument on Nov. 22, 1996, operated by NRAO and supported by the NASA
High Energy Astrophysics program. The GBI was then used as a two telescope interferometer that operated simultaneously at 2.7 and 8.3 GHz to monitor transient
, galactic X-ray binaries, AGN
's and Gamma-ray sources. Amongst the prime sources were GRS 1915+105
, GRO J1655-40
, Cyg X-3
, Cyg X-1, GRS 1716-249, SS433, and LS I +61 303
.
On the October 6, 2000 the GBI monitoring program has ceased due to lack of funding.
Radio astronomy
Radio astronomy is a subfield of astronomy that studies celestial objects at radio frequencies. The initial detection of radio waves from an astronomical object was made in the 1930s, when Karl Jansky observed radiation coming from the Milky Way. Subsequent observations have identified a number of...
telescope
Telescope
A telescope is an instrument that aids in the observation of remote objects by collecting electromagnetic radiation . The first known practical telescopes were invented in the Netherlands at the beginning of the 1600s , using glass lenses...
located at Green Bank
Green Bank, West Virginia
Green Bank is a census-designated place in Pocahontas County in West Virginia's Potomac Highlands inside the Allegheny Mountain Range. Green Bank is located along WV 28. Green Bank is also close to the Snowshoe Mountain ski resort...
, West Virginia
West Virginia
West Virginia is a state in the Appalachian and Southeastern regions of the United States, bordered by Virginia to the southeast, Kentucky to the southwest, Ohio to the northwest, Pennsylvania to the northeast and Maryland to the east...
(USA
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
) and operated by the National Radio Astronomy Observatory (NRAO). It included three radio telescopes of 85-foot (26m) diameter, designated 85-1, 85-3, and 85-2 (85-1 is also known as the Tatel Telescope).
The GBI began operation in 1964 as a two element interferometer in order to test large aperture synthesis
Aperture synthesis
Aperture synthesis or synthesis imaging is a type of interferometry that mixes signals from a collection of telescopes to produce images having the same angular resolution as an instrument the size of the entire collection...
arrays and study radio astrometry
Astrometry
Astrometry is the branch of astronomy that involves precise measurements of the positions and movements of stars and other celestial bodies. The information obtained by astrometric measurements provides information on the kinematics and physical origin of our Solar System and our Galaxy, the Milky...
and interstellar scintillation
Scintillation (astronomy)
Scintillation or twinkling are generic terms for rapid variations in apparent brightness or color of a distant luminous object viewed through a medium, most commonly the atmosphere ....
. In 1967 the array was upgraded with construction of the third element. From 1978-1996, it was operated in support of USNO and NRL
United States Naval Research Laboratory
The United States Naval Research Laboratory is the corporate research laboratory for the United States Navy and the United States Marine Corps and conducts a program of scientific research and development. NRL opened in 1923 at the instigation of Thomas Edison...
geodetic and astronomy programs, but then briefly suspended operations.
The Green Bank Interferometer (GBI) resumed operation as a radio monitoring instrument on Nov. 22, 1996, operated by NRAO and supported by the NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
High Energy Astrophysics program. The GBI was then used as a two telescope interferometer that operated simultaneously at 2.7 and 8.3 GHz to monitor transient
Transient astronomical event
A transient astronomical event, often simply called in context by astronomers a transient, is an astronomical object or phenomenon which can be observed for a short period of time...
, galactic X-ray binaries, AGN
Active galactic nucleus
An active galactic nucleus is a compact region at the centre of a galaxy that has a much higher than normal luminosity over at least some portion, and possibly all, of the electromagnetic spectrum. Such excess emission has been observed in the radio, infrared, optical, ultra-violet, X-ray and...
's and Gamma-ray sources. Amongst the prime sources were GRS 1915+105
GRS 1915+105
GRS 1915+105 or V1487 Aquilae is an X-ray binary star system which features a regular star and a black hole. It was discovered on August 15, 1992 by the WATCH all-sky monitor aboard Granat. "GRS" stands for "GRANAT source", "1915" is the right ascension and "105" is declination in units of 0.1...
, GRO J1655-40
GRO J1655-40
|-! style="background-color: #FFFFC0;" colspan="2" | Astrometry|- style="vertical-align: top;"| Spectral type | F5IV|- style="vertical-align: top;"| Apparent magnitude | 17.0|- style="vertical-align: top;"| Distance | 5,500—11,000 ly...
, Cyg X-3
Cygnus x-3
Cygnus X-3 is one of the stronger binary X-ray sources in the sky.Classified as a microquasar, it is believed to be a compact object in a binary system which is pulling in a stream of gas from an ordinary star companion....
, Cyg X-1, GRS 1716-249, SS433, and LS I +61 303
LS I +61 303
LS I +61 303 is a binary system harboring a compact object and a massive star that emits HE and VHE gamma rays. It is only one of three known star systems that produce such energetic rays...
.
On the October 6, 2000 the GBI monitoring program has ceased due to lack of funding.
Technical Data: 2-element interferometer
- Baseline: 2400 meters at an azimuth of 62 degrees (E of N).
- Bands: 8.3 GHz (X-band) and 2.25 GHz (S-band) with 35 MHz bandwidth.
- Receivers: Cryogenically cooled, dual frequency, dual polarization. Both X and S bands simultaneously observed in both right and left circular polarizations.
- System temperature: About 35 K in Sband and 45 K in Xband.
- Sensitivity: RMS noise in a 5-minute scan is about 6 mJy in S-band and 10 mJy in X-band for point sources.
- Minimum integration time: 30 seconds.
- Resolution: About 3 arcseconds fringe at X-band and 11 arcseconds at S-band.