Estimation of orbital inclination angle for compact binary mergers

The joint detection of gravitational wave (GW) event GW 170817 and the short-duration gamma-ray burst (GRB) event GRB 170817A, marked the beginning of GW multi-messenger astronomy and confirmed that binary neutron star mergers are progenitors of at least some short GRBs. An estimated joint detection rate of 0.3 - 1.7 per year between the LIGO Hanford, LIGO Livingston and Virgo GW network at design sensitivity, and the Fermi Gamma-ray Burst Monitor was predicted. However, to date, GW 170817/GRB 170817A joint detection has been the only event of its kind so far. Taking into the account that GRBs are narrowly beamed, we propose that previous mergers involving neutron stars, were orientated such that observation of the emitted GRB along the narrow jet was not possible. To support this hypothesis we aim to determine the inclination of previously detected Binary Neutron Star and Black Hole Neutron Star mergers through GW analysis. Here we present a preliminary analysis to estimate the orbital inclination parameter of GW 170817 based on different GW waveform models using BILBY, a Bayesian parameter estimation python library. Using only GW data, the inclination of the progenitor system of GW 170817 was found to be ≈ 152^◦, in agreement with constraints on this value through observations of GRB 170817A.