High Quality Content by WIKIPEDIA articles! The Gamma-ray burst Coordinates Network (GCN) is a system that distributes information about the location of a Gamma-ray burst (GRB), called Notices, when a burst is detected by various spacecraft. The GCN also automatically receives and distributes messages, called Circulars, about follow-up observations to interested individuals and institutions. Follow-up observations may be made by ground-based and space-based optical, radio, and X-ray observatories.