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(abridged) Three-dimensional hydrodynamic simulations with an Eulerian PPMcode are presented for the time-dependent evolution of accretion tori aroundnonrotating and rotating stellar-mass black holes (BHs), using apseudo-Newtonian gravitational potential to approximate the effects of generalrelativity. The initial configurations are assumed to be remnants of binaryneutron star (NS) or NS+BH mergers and consist of a 4 solar mass BH with variedspin, girded by a torus with a mass between 0.01 and 0.2 solar masses. Theevolution of tori without and with physical shear viscosity is simulated, usinga realistic equation of state and following the energy loss and lepton numberchange due to neutrino emission by a neutrino-trapping scheme. Thetime-dependent efficiency of converting rest-mass energy to neutrinos is foundto reach 10 percent, the efficiency of converting neutrino energy into apair-photon fireball by neutrino annihilation can reach several percent. Therate of the latter process declines with time much less steeply than the totalneutrino luminosity, because the ongoing protonization of the torus ensures arather stable product of neutrino and antineutrino luminosities. The neutrinoemission increases steeply with higher viscosity, larger torus mass, and largerBH spin in corotation with the torus. For rotation rates as expected forpost-merger BHs (a > 0.5) and reasonable values of the alpha viscosity (alpha ~0.1), the considered tori release sufficient energy in neutrinos to account forthe energetics of the well-localized short gamma-ray bursts recently detectedby Hete and Swift, if collimation is invoked as predicted by hydrodynamic jetsimulations.Comment: 23 pages, 15 figures (high resolution available upon request),  accepted by Astron. Astrophys. Significantly shortened with respect to first  versio

Three-dimensional simulations of non-stationary accretion by remnant black holes of compact object mergers