Page "Gamma-ray burst" Paragraph 17

Although some light curves can be roughly reproduced using certain simplified models, little progress has been made in understanding the full diversity observed.

Many classification schemes have been proposed, but these are often based solely on differences in the appearance of light curves and may not always reflect a true physical difference in the progenitors of the explosions.

However, plots of the distribution of the observed duration for a large number of gamma-ray bursts show a clear bimodality, suggesting the existence of two separate populations: a " short " population with an average duration of about 0. 3 seconds and a " long " population with an average duration of about 30 seconds.

Both distributions are very broad with a significant overlap region in which the identity of a given event is not clear from duration alone.

Additional classes beyond this two-tiered system have been proposed on both observational and theoretical grounds.