  The collapsar model is the most promising scenario to explain the huge
release of energy associated with long duration gamma-ray-bursts (GRBs). Within
this scenario GRBs are believed to be powered by accretion through a
rotationally support torus or by fast rotation of a compact object. In both
cases then, rotation of the progenitor star is one of the key properties
because it must be high enough for the torus to form, the compact object to
rotate very fast, or both. Here, we check what rotational properties a
progenitor star must have in order to sustain torus accretion over relatively
long activity periods as observed in most GRBs. We show that simple, often
cited, estimates of the total mass available for torus formation and
consequently the duration of a GRB are only upper limits. We revise these
estimates by taking into account the long term effect that as the compact
object accretes the minimum specific angular momentum needed for torus
formation increases. This in turn leads to a smaller fraction of the stellar
envelope that can form a torus. We demostrate that this effect can lead to a
significant, an order of magnidute, reduction of the total energy and overall
duration of a GRB event. This of course can be mitigated by assuming that the
progenitor star rotates faster then we assumed. However, our assumed rotation
is already high compared to observational and theoretical constraints. We also
discuss implications of our result.
