Today astronomers have a pretty good idea what gamma-ray bursts are, thanks to missions such as Swift. However, when Ginga launched, gamma-ray bursts were still largely a mystery.
Gamma-ray bursts (or GRBs) were discovered by accident in data from the Vela satellites in the late 1960s (the results were published in 1973). As the name implies, a gamma-ray burst is a sudden burst of gamma-rays observed in the sky. GRBs appear at a random directions in the sky, then quickly fade or disappear. Fifteen years after their first discovery, when Ginga was launched, astronomers had been able to determine the positions of many GRBs, they were able to determine that they were probably very far away (outside our own galaxy), and they were able to find optical flashes that possibly coincided with a few GRBs. Astronomers were beginning to put together a picture, but needed more detailed observations in more wavelengths to complete the puzzle.
The Gamma-ray Burst Detector (GBD) on Ginga was the first GRB detector aimed at monitoring bursts at energies lower than 30 keV. It accomplished this by using two different detectors: a proportional counter that observed the 2 to 30 keV range and a scintillation detector that observed the 14 to 400 keV range.
