Aims.A model of jet precession driven by a neutrino-cooled disk around a spinning black hole is presented to explain the temporal structure and spectral evolution of gamma-ray bursts (GRBs). Methods. The differential rotation of the outer part of a neutrino-dominated accretion disk may result in precession of the inner part of the disk and the central black hole, hence driving a precessed jet via neutrino annihilation around the inner part of the disk. Results. Both analytic and numeric results for our model are presented. Our calculations show that a black-hole, accretion-disk system with the black hole mass M 3.66 M , accretion rateṀ 0.54 M s −1 , spin parameter a = 0.9, and viscosity parameter α = 0.01 may drive a precessed jet with period P = 1 s and luminosity L = 10 51 erg s −1 , corresponding to the scenario for long GRBs. A precessed jet with P = 0.1 s and L = 10 50 erg s −1 may be powered by a system with M 5.59 M ,Ṁ 0.74 M s −1 , a = 0.1, and α = 0.01, and is possibly responsible for the short GRBs. Both the temporal and spectral evolution in GRB pulse may be explained with our model. Conclusions. GRB central engines most likely power a precessed jet driven by a neutrino-cooled disk. The global GRB lightcurves thus could be modulated by the jet precession during the accretion timescale of the GRB central engine. Both the temporal and spectral evolution in GRB pulse may stem from a viewing effect of the jet precession.

We revisit the vertical structure of black hole accretion disks in spherical coordinates. By comparing the advective cooling with the viscous heating, we show that advection-dominated disks are geometrically thick, i.e., with the half-opening angle ∆θ > 2π/5, rather than slim as supposed previously in the literature.

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