THE COMPTON GAMMA RAY OBSERVATORIEBy: Windell Barfield and Landris Baggs

WHY THEY BUILT IT/ PURPOSE

• The Compton Gamma Ray Observatory (GGRO) was a sophisticated satellite

observatory dedicated to observing the high-energy Universe.

• It was designed to receive gamma rays, very high-energy and short-

wavelength electromagnetic radiation produced from subatomic particle

interactions

• It was the second satellite in NASA’s Great Observatories Program

ENGINEERING

• It featured four critically important telescopes, which were:

1. Burst and Transient Source Experiment, (BATSE): searched the sky for gamma ray bursts.

2. The Oriented Scintillation Spectrometer Experiment, (OSSE), detected gamma rays entering the field of

view of any of four detector modules.

3. The Imaging Compton Telescope, (COMPTEL), tuned to the 0.75-30 MeV energy range and determined

the angle of arrival of photons to within a degree.

4. The Energetic Gamma Ray Experiment Telescope, (EGRET) measured high energy (20 MeV to 30 GeV)

gamma ray source positions to a fraction of a degree and photon energy to within 15 percent.

RESULTS/DATA• The EGRET instrument conducted the first all sky survey above 100 MeV. Using four years of data it discovered 271 sources, 170 of which were

unidentified.

• The COMPTEL instrument completed an all sky map of 26

• Al (a radioactive isotope of aluminum).

• The OSSE instrument completed the most comprehensive survey of the galactic center, and discovered a possible antimatter "cloud" above the center.

• The BATSE instrument averaged one gamma ray burst event detection per day for a total of approximately 2700 detections. It definitively showed that

the majority of gamma-ray bursts must originate in distant galaxies, not nearby in our own Milky Way, and therefore must be enormously energetic.

• The discovery of the first four soft gamma ray repeaters; these sources were relatively weak, mostly below 100 keV and had unpredictable periods of

activity and inactivity

• The separation of GRBs into two time profiles: short duration GRBs that last less than 2 seconds, and long duration GRBs that last longer than this.

RESULTS/ DATA CONTINUED

• The completion of both a pulsar survey and a supernova remnant survey

• The discovery of terrestrial gamma ray sources in 1994 that came from

thunderclouds

WHAT HAPPENED TO IT?

• After one of its 3 gyroscopes failed in December 1999, the observatory was

deliberately de-orbited.

• At the time, the observatory was still operational, however the failure of

another gyroscope would have made de-orbiting much more difficult and

dangerous.

• The debris from the satellite landed out in the Pacific Ocean.