How does the shape of gamma-ray bursts' pulses affect the duration
  distribution?
  Gamma-ray bursts (GRBs) come in two types, short and long. The distribution
of logarithmic durations of long GRBs is asymmetric rather than Gaussian. Such
an asymmetry, when modelled with a mixture of Gaussian distributions, requires
an introduction of an additional component, often associated with another class
of GRBs. However, when modelled with inherently asymmetric distributions, there
is no need for such a component. The cosmological dilation was already ruled
out as a source of the asymmetry, hence its origin resides in the progenitors.
GRB light curves (LCs) are usually well described by a series of
fast-rise-exponential-decay pulses. A statistical analysis of ensembles of
simulated LCs shows that the asymmetry is a natural consequence of the pulse
shape and the multi-pulse character of the LCs.
