  We study the structure and evolution of the hyperaccreting disks and outflows
in the gamma ray bursts central engines. The torus around a stellar mass black
hole is composed of free nucleons, Helium, electron-positron pairs, and is
cooled by neutrino emission. Accretion of matter powers the relativistic jets,
responsible for the gamma ray prompt emission. The significant number density
of neutrons in the disk and outflowing material will cause subsequent formation
of heavier nuclei. We study the process of nucleosynthesis and its possible
observational consequences. We also apply our scenario to the recent
observation of the gravitational wave signal, detected on September 14th, 2015
by the two Advanced LIGO detectors, and related to an inspiral and merger of a
binary black hole system. A gamma ray burst that could possibly be related with
the GW150914 event was observed by the Fermi satellite. It had a duration of
about 1 second and appeared about 0.4 seconds after the gravitational-wave
signal. We propose that a collapsing massive star and a black hole in a close
binary could lead to the event. The gamma ray burst was powered by a weak
neutrino flux produced in the star remnant's matter. Low spin and kick velocity
of the merged black hole are reproduced in our simulations. Coincident
gravitational-wave emission originates from the merger of the collapsed core
and the companion black hole.
