Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009aas...21335207p&link_type=abstract
American Astronomical Society, AAS Meeting #213, #352.07; Bulletin of the American Astronomical Society, Vol. 41, p.493
Astronomy and Astrophysics
Astronomy
1
Scientific paper
Within the collapsar model, GRBs are believed to be powered by accretion through a rotationally supported torus or a rotating compact object. In both cases, rotation of the progenitor star is a key property, because it must be high enough for the torus to form, the compact object to rotate very fast, or both. Here, we investigate the formation of a torus around a spinning black hole (BH) and we check what rotational properties a progenitor must have in order to sustain torus accretion over relatively long activity periods. We also study the time evolution of the BH spin parameter. We take into account the coupling between the mass and spin of BH and the critical specific angular momentum of accreting gas, needed for the torus to form. The large BH spin reduces the critical angular momentum which in turn can increase the GRB duration with respect to the Schwarzschild BH case. We quantify this effect and estimate the GRB durations in three cases: when a hyper accreting torus operates or a BH spins very fast or both. We show under what conditions a given progenitor star produces a burst that can last as short as several seconds and as long as several hundred of seconds. Our models indicate that it is possible for a single collapse to produce three kinds of jets: (1) a very short, lasting between a fraction of a second and a few seconds, 'precursor' jet, powered only by a hyper accreting torus before the BH spins up, (2) an 'early' jet, lasting several tens of seconds and powered by both hyper accretion and BH rotation, and (3) a 'late' jet, powered only by the spinning BH. This work was supported in part by NASA under grant NNG05GB68G.
Janiuk Agnieszka
Moderski Rafal
Proga Daniel
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