Various other incorrect interpretations have been suggested, such as " lack of shoulders " ( where the " shoulder " is defined vaguely as the area between the peak and the tail, or more specifically as the area about one standard deviation from the mean ) or " bimodality ".
12.
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.
