Can a black hole-neutron star merger explain GW170817, AT2017gfo, and GRB170817A?

The discovery of the compact binary coalescence in both gravitational waves and electromagnetic radiation marks a breakthrough in the field of multimessenger astronomy and has improved our knowledge in a number of research areas. However, an open question is the exact origin of the observables and if one can confirm reliably that GW170817 and its electromagnetic counterparts resulted from a binary neutron star merger. To answer the question if the observation of GW170817, GRB170817A, and AT2017gfo could be explained by the merger of a neutron star with a black hole, we perform a joint multimessenger analysis of the gravitational waves, the short gamma-ray burst, and the kilonova. Assuming a black hole-neutron star system, we derive multimessenger constraints for the tidal deformability of the neutron star of Lambda > 425 and for the mass ratio of q < 2.03 at 90% confidence, with peaks in the likelihood near Lambda = 830 and q = 1.0. Overall, we find that a black hole-neutron star merger could explain the observed signatures; however, our analysis shows that a binary neutron star origin of GW170817 seems more plausible.