In the preflare stage (13:50 to 13:56 UT), the soft X-ray emission gradually increased, but little if any hard X-rays or gamma rays were detected above the instrumental background level. This was followed by the so-called impulsive phase, in which the hard X-ray and gamma-ray emission rose impulsively, often with many short but intense spikes of emission, each lasting a few seconds to tens of seconds. (Data and description courtesy NASA.)