Forerunner of GLAST, the CGRO-EGRET experiment
The EGRET telescope was developed as part of the Compton Gamma Ray Observatory (CGRO), so the Compton needs to be discussed to better understand the EGRET. The CGRO was the second of the Great Observatories which were developed by NASA, and followed the great Hubble Space Telescope, the Chandra X-ray Observatory, and the Spitzer Space Telescope.
The Compton was named after Dr. Arthur Holly Compton–the famous Nobel Prize winner known for his work involved with gamma ray physics—the Compton was launched on the Atlantis space shuttle in 1991. Known for being the heaviest astrophysical payload ever flown at that time, the CGRO was deployed in low earth orbit in order to avoid the Van Allen radiation belt. It was deliberately de-orbited by NASA after one of its gyroscopes failed, yet was still considered operational. After considering the risks if another gyroscope would fail, NASA decided to do a controlled crash in the Pacific Ocean in the interest of public safety on June 4, 2000.
The Energetic Gamma Ray Experiment Telescope (EGRET) was from the Compton Gamma Ray Observatory satellite, consisting of one out of four instruments in the Compton. It became best known for conducting the first all sky survey above 100 MeV whose original job was to detect individual gamma rays with energy from 30 MeV to 30GeV. The four years of data–it discovered 271 point sources of high-energy gamma rays, 170 of that were unidentified with any objects visible in other wavelength bands. Identified sources are usually considered to be blazars, pulsars, and other objects.
As of 2002, there were 420 known discrete gamma ray sources. The EGRET was responsible for recognizing most of them, located on the Compton Gamma-Ray Observatory. With the newly developed GLAST All-Sky Survey to be completed by the late 2000s, this number should increase by a factor of 30 to be over 10,000. These numbers, according to NASA, can be compared to the ~1-2 possible gamma-ray sources known about 1970, and the ~25 confirmed sources by 1990. This information is mostly discovered by the COS-B mission.
This entry was posted on Wednesday, September 19th, 2007 at 11:42 am and is filed under Mission History, Public Relations, Space Agency News. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.
