Green Bank Interferometer
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.
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.