High Quality Content by WIKIPEDIA articles! GRB 970228 was the first gamma-ray burst (GRB) for which an afterglow was observed. It was detected on 28 February 1997 at 02:58 UTC. Since 1993, physicists had predicted GRBs to be followed by a lower-energy afterglow (in wavelengths such as radio waves, x-rays, and even visible light), but until this event, GRBs had only been observed in highly luminous bursts of high-energy gamma rays (the most energetic form of electromagnetic radiation).