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In the frame of the collapsar model for long gamma ray bursts (GRBs), weinvestigate the formation of a torus around a spinning BH and we check whatrotational properties a progenitor star must have in order to sustain torusaccretion over relatively long activity periods. We also study the timeevolution of the BH spin parameter. We take into account the coupling betweenBH mass, its spin parameter and the critical specific angular momentum ofaccreting gas, needed for the torus to form. The large BH spin reduces thecritical angular momentum which in turn can increase the GRB duration withrespect to the Schwarzschild BH case. We quantify this effect and estimate theGRB durations in three cases: when a hyper accreting torus operates or a BHspins very fast or both. We show under what conditions a given progenitor starproduces a burst that can last as short as several seconds and as long asseveral hundred of seconds. Our models indicate that it is possible for asingle collapse to produce three kinds of jets: (1) a very short, lastingbetween a fraction of a second and a few seconds, 'precursor' jet, powered onlyby a hyper accreting torus before the BH spins up, (2) an 'early' jet, lastingseveral tens of seconds and powered by both hyper accretion and BH rotation,and (3) a 'late' jet, powered only by the spinning BH.

On the duration of long GRBs: effects of black hole spin