Evolution of a neutrino-cooled disc in gamma-ray bursts

Rapid, hyper-Eddington accretion is likely to power the central engines of gamma-ray bursts (GRBs). In the extreme conditions of densities and temperatures the accreting torus is cooled by neutrino emission rather than by radiation. Another important cooling mechanism is the advection of energy into the central black hole. We compute the time evolution of a neutrino-dominated disc that proceeds during the burst and investigate the changes in its density and temperature. The discrimination between short and long bursts is made on the basis of the different rates of material inflow to the outer parts of the disc, thus favouring the binary merger scenario for the short GRBs and the collapsar scenario for the long GRBs. Within the context of the collapsar model, we also study the evolution of the photon luminosity of the remnant disc up to times of similar to1 d, and we discuss its implications for the production of emission lines in GRB spectra.