  This is the second of a series of catalogs of gamma-ray bursts (GRBs)
observed with the Fermi Gamma-ray Burst Monitor (GBM). It extends the first
two-year catalog by two more years, resulting in an overall list of 953 GBM
triggered GRBs. The intention of the GBM GRB catalog is to provide information
to the community on the most important observables of the GBM detected GRBs.
For each GRB the location and main characteristics of the prompt emission, the
duration, peak flux and fluence are derived. The latter two quantities are
calculated for the 50 - 300 keV energy band, where the maximum energy release
of GRBs in the instrument reference system is observed and also for a broader
energy band from 10 - 1000 keV, exploiting the full energy range of GBMs
low-energy detectors. Furthermore, information is given on the settings and
modifications of the triggering criteria and exceptional operational conditions
during years three and four in the mission. This second catalog is an official
product of the Fermi GBM science team, and the data files containing the
complete results are available from the High-Energy Astrophysics Science
Archive Research Center (HEASARC).
