  General relativistic simulations for the merger of binary neutron stars are
performed as an extension of a previous work\cite{Shibata:2006nm}. We prepare
binary neutron stars with a large initial orbital separation and employ the
moving-puncture formulation, which enables to follow merger and ringdown phases
for a long time, even after black hole formation. For modeling inspiraling
neutron stars, which should be composed of cold neutron stars, the
Akmal-Pandhalipande-Ravenhall (APR) equation of state (EOS) is adopted. After
the onset of the merger, the hybrid-type EOS is used; i.e., the cold and
thermal parts are given by the APR and $\Gamma$-law EOSs, respectively. Three
equal-mass binaries each with mass $1.4M_\odot,1.45M_\odot,1.5M_\odot$ and two
unequal-mass binaries with mass 1.3--$1.6M_\odot$, 1.35--$1.65M_\odot$ are
prepared. We focus primarily on the black hole formation case, and explore mass
and spin of the black hole, mass of disks which surround the black hole, and
gravitational waves emitted during the black hole formation. We find that (i)
for the systems of $m_0=2.9$--$3.0M_\odot$ and of mass ratio $\approx 0.8$, the
mass of disks which surround the formed black hole is 0.006--$0.02M_{\odot}$;
(ii) the spin of the formed black hole is $0.78 \pm 0.02$ when a black hole is
formed after the merger in the dynamical time scale. This value depends weakly
on the total mass and mass ratio, and is about 0.1 larger than that of a black
hole formed from nonspinning binary black holes; (iii) for the black-hole
formation case, Fourier spectrum shape of gravitational waves emitted in the
merger and ringdown phases has a universal qualitative feature irrespective of
the total mass and mass ratio, but quantitatively, the spectrum reflects the
parameters of the binary neutron stars.
