What is the Compton Gamma Ray Observatory?

The Compton Gamma Ray Observatory (Compton Gamma Ray Observatory, abbreviated as CGRO) is a gamma-ray astronomy satellite launched by the National Aeronautics and Space Administration (NASA) in 1991 and is a large orbiting observatory Planned second satellite. It is named after Compton, an American physicist who made an important contribution in the field of gamma rays, and aims to observe the gamma-ray radiation of celestial bodies.

Compton Gamma Ray Astronomy (CGRO) is a space observatory that detects light from 20 keV to 30 GeV in Earth orbit from 1991 to 2000. Its one spacecraft contains four main telescopes covering X-rays and gamma-rays, including instruments and detectors. After 14 years of hard work, the observatory was launched on April 5, 1991 by the space shuttle Atlantis in flight number STS-37, and began operation on June 4, 2000. ^[1]

The Compton Gamma Ray Observatory weighed about 17 tons, of which the astronomical instrument weighed about 7 tons. At that time, it was the heaviest civilian spacecraft launched by the space shuttle. The main observation instruments carried on the satellite are:

• The Burst and Transient Source Test Equipment (BATSE) consists of eight identical NaI detection modules and is installed at eight corners of the satellite. The observation energy range is 20-600 keV, the purpose is to detect short-term gamma-ray bursts. BATSE was developed by NASA's Marshall Space Flight Center.

• Directional scintillation spectrometer (OSSE), consisting of 4 detectors, is divided into two groups. Each time a target celestial body is observed, one group is directed at the celestial body to monitor its own radiation, and the other is directed at the sky near the celestial body to monitor background radiation The roles of the two groups are regularly swapped. The energy range is 0.05-10 MeV and is manufactured by the US Naval Research Laboratory.

• The Compton Imaging Telescope (COMPTEL), with an observation energy range of 0.75-30 MeV, was jointly developed by the Max Planck Institute in Germany, the University of New Hampshire, and the Astrophysics Division of the European Space Agency. It observed the 1.809 MeV lines of aluminum during its work and found that they are concentrated on the galactic plane and are mainly distributed near the center of the galaxy and spiral arms, indicating that the heavy elements mainly come from massive stars.

• High Energy Gamma Ray Test Telescope (EGRET) is used to observe high energy gamma rays of 20 MeV-30 GeV, and has extremely high time resolution ability. The instrument was jointly developed by NASA Goddard Space Flight Center, Max Planck Institute, and Stanford University. During its work, it detected a group of BL celestial bodies of high-energy gamma-ray radiation, and increased the number of gamma-ray pulsars to eight. It also gave a number of high-energy radiation from gamma-ray bursts.

The Compton Gamma Ray Observatory conducted two sky surveys during the orbit. The first survey observed the Crab Nebula, X-1 Cygnus, X-3 Cygnus, NGC 4151 and other objects, July 1991 The second survey began including the Milky Way Center, Supernova 1987A, etc., and 271 gamma-ray sources were discovered in 4 years. Flare bursts of the sun were observed in 1991; high-energy explosive radiation from celestial bodies such as X-3 and Supernova 1987A were monitored for a long time. The fourth gamma-ray pulsar PSR1706-44 was discovered in 1991, with a radio pulse period of 102 milliseconds; in 1997, a line generated by the annihilation of positrons and positrons with an energy of 511 keV near the center of the Milky Way was discovered, indicating the existence of a huge antimatter Jet; recorded about 2700 gamma-ray bursts, and found that their distribution in the sky is isotropic, supporting the idea that gamma-ray bursts occur on the cosmological scale. Gamma-ray bursts are divided into two types of long bursts and short bursts based on the observation data accumulated by them. In 1999, the famous gamma-ray burst GRB 990123 was also observed, which indirectly triggered the afterglow of its optical band. Observed by ground telescope.

• The EGRET instrument performed the first all-weather measurement of more than 100 MeV. Using four years of data, it found 271 sources, of which 170 were unidentified sources.

• OSSE Instruments completed the most comprehensive survey of the Galaxy Center and found a possible antimatter "cloud" above the center.

• BATSE instruments detect gamma-ray emergencies on average once a day, for a total of about 2,700 tests. It definitely shows that most gamma-ray bursts must originate from distant galaxies, not near our own Milky Way, and therefore must be very severe.

• The first four soft gamma repetitive bursts were found; these sources are relatively weak, most of which are below 100 keV, with unpredictable periods of activity and inactivity.

The Compton Gamma Ray Observatory has a design life of 5 years, but has been in operation for 9 years. On December 6, 1999, a gyroscope on the satellite for attitude control failed due to a spherical axis failure. There are three gyroscopes installed on the satellite, and two satellites must work simultaneously for normal operation. If another gyroscope is damaged, it will cause the satellite to lose control and may eventually crash in a densely populated area. After losing the backed up gyroscope, some astronomers thought it might still make important scientific observations and still strongly advocated to extend its life, but for security reasons, NASA decided to abandon the satellite. On May 26, 2000, after returning the last solar observation data, NASA directed the satellite to start a series of ignitions, and finally guided it to fall into the Earth's atmosphere on June 4, burned over the Pacific Ocean, and debris fell in southwestern Hawaii. About 3200-4000 kilometers of the intended sea area.