Spacecraft find Gamma-Ray Bursts

A gamma-ray burst (GRB) can occur when a nuclear bomb is detonated. But even more powerful GRBs may occur when neutron stars merge and a black hole is the result. Here is how cosmological GRBs were first detected.

After the nuclear test ban treaty was signed, the U.S. Air Force launched a satellite to detect cheating. A number of these Vela satellites were launched with each version more sophisticated than the previous. Detections that were clearly not nuclear blasts were saved for later research. In 1973, a paper was written which listed 16 GRBs detected between 1969 and 1972 by the Vela 5 and 6 satellites. The direction of these GRBs could be determined by comparing the time deltas between when two (or more) spacecraft made the detection. This showed that the GRBs were clearly not from earth or solar origins.

An even earlier GRB was detected on July 2, 1967 but the satellites (Vela 4 at this time) did not have the ability to make the critical timing comparison so it could not determine the direction that it came from. In retrospect, it appeared very similar to the GRBs from 1973 and this was written up in 1976. Some say that the work on GRB research was kept secret for cold-war reasons but the reality appears to be less dramatic.

In 1991, NASA launched the second of the “great observatories” as the Compton Gamma Ray Observatory. Compton was used to determine that GRBs come in two varieties, short duration and long duration. BeppoSAX was an X-ray astronomy satellite, a project of the Italian Space Agency. It found some of the first GRB locations. The Swift spacecraft is the most recent and most sophisticated GRB observatory ever constructed. It has three instruments that allow Swift to inspect a GRB across a wide part of the EMR spectrum. Swift detected GRB080319 in March of 2008 and it is the brightest GRB to date. The star brightened for 15 seconds and was as bright as magnitude 5.3. The star had a look-back time of 7.5 billion years.