{em Fermi}/GBM Short Gamma-ray Burst Catalog and Case Study for GRB 170817A/GW 170817

Motivating by the discovery of association between GW 170817 and sGRB 170817A, we present a comprehensive analysis for sGRBs observed with Fermi/GBM in 9 operation years and study the properties of sGRB 170817A -like events. We derive a catalog of 275 typical sGRBs and 48 sGRB 170817A-like weak events from the GBM data of 2217 GRBs. We visibly identify two patterns of their light curve, single episode (Pattern I, 61% of the SGRBs) and multiple episodes (Pattern II, 39% of the SGRBs). Their duration distribution shows a tentative bimodal feature. Their spectra can be fitted with a cutoff power-law model, except for 4 sGRBs, and the spectral indices normally distribute at $Gamma=0.69pm 0.40$. Their $E_p$ values show a tentative bimodal distribution with peaks at 145 keV and 500 keV. No correlation among $T_{90}$, $E_p$, and $Gamma$ is found. GRB 170817A is a soft, weak sGRB with $ E_{p}=124pm 106$ keV, $L_{rm iso}=(5.67pm4.65)times10^{46}rm ~erg~s^{-1}$, and $E_{rm iso}=(3.23pm2.65)times10^{46}rm ~erg$. It follows the $E_{rm iso}-E_{rm p}$ relation of typical short GRBs. Its lightcurve is of Pattern II. Two lightcurve patterns, together with the potential two components in the $E_{rm p}$ and $T_{90}$ distributions, we suspect that the current sample may include two distinct types of sGRBs from different progenitors. sGRB 170817A-like events may be from NS-NS mergers and those sGRBs with a Pattern I lightcurve may be from another distinct type of compact binary.