  Hypercritical accretion flows onto stellar mass black holes (BHs) are
commonly considered as a promising model of central engines of gamma-ray bursts
(GRBs). In this model a certain fraction of gravitational binding energy of
accreting matter is deposited to the energy of relativistic jets via neutrino
annihilation and/or magnetic fields. However, some recent studies have
indicated that the energy deposition rate by neutrino annihilation is somewhat
smaller than that needed to power a GRB. To overcome this difficulty,
Ramirez-Ruiz & Socrates (2005) proposed that high energy neutrinos from hot
corona above the accretion disk might enhance the efficiency of energy
deposition. We elucidate the disk corona model in the context of hypercritical
accretion flows. From the energy balance in the disk and the corona, we can
calculate the disk and coronal temperature, Td and Tc, and neutrino spectra,
taking into account the neutrino cooling processes by neutrino-electron
scatterings and neutrino pair productions. The calculated neutrino spectra
consist of two peaks; one by the neutrino emission from the disk and the other
by that from the corona. We find that the disk corona can enhance the
efficiency of energy release but only by a factor of 1.5 or so, unless the
height of the corona is very small, H<<r. This is because the neutrino emission
is very sensitive to the temperature of emitting region, and then the ratio
Tc/Td cannot be so large.
