  We present the second Swift Burst Alert Telescope (BAT) catalog of gamma-ray
bursts (GRBs), which contains 476 bursts detected by the BAT between 2004
December 19 and 2009 December 21. This catalog (hereafter the BAT2 catalog)
presents burst trigger time, location, 90% error radius, duration, fluence,
peak flux, time-averaged spectral parameters and time-resolved spectral
parameters measured by the BAT. In the correlation study of various observed
parameters extracted from the BAT prompt emission data, we distinguish among
long-duration GRBs (L-GRBs), short-duration GRBs (S-GRBs), and short-duration
GRBs with extended emission (S-GRBs with E.E.) to investigate differences in
the prompt emission properties. The fraction of L-GRBs, S-GRBs and S-GRBs with
E.E. in the catalog are 89%, 8% and 2% respectively. We compare the BAT prompt
emission properties with the BATSE, BeppoSAX and HETE-2 GRB samples. We also
correlate the observed prompt emission properties with the redshifts for the
GRBs with known redshift. The BAT T90 and T50 durations peak at 70 s and 30 s,
respectively. We confirm that the spectra of the BAT S-GRBs are generally
harder than those of the L-GRBs. The time-averaged spectra of the BAT S-GRBs
with E.E. are similar to those of the L-GRBs. Whereas, the spectra of the
initial short spikes of the S-GRBs with E.E. are similar to those of the
S-GRBs. We show that the BAT GRB samples are significantly softer than the
BATSE bright GRBs, and that the time-averaged Epeak of the BAT GRBs peaks at 80
keV which is significantly lower energy than those of the BATSE sample which
peak at 320 keV. The time-averaged spectral properties of the BAT GRB sample
are similar to those of the HETE-2 GRB samples. By time-resolved spectral
analysis, we find that only 10% of the BAT observed photon indices are outside
the allowed region of the synchrotron shock model.
