Follow-up analyses of the binary-neutron-star signals GW170817 and GW190425 by using post-Newtonian waveform models

We reanalyze the binary-neutron-star signals, GW170817 and GW190425, focusing on the inspiral regime. We use post-Newtonian waveform models as templates, which are theoretically rigid and efficiently describe the inspiral regime. We study potential systematic difference in estimates of the binary tidal deformability by using different descriptions for the point-particle dynamics and tidal effects. We find that the estimates of show no significant systematic difference among three models for the point-particle parts: TF2, TF2g, and TF2+, when they employ the same tidal model. We compare different tidal descriptions given by different post-Newtonian orders in the tidal phase. Our results indicate that the estimates of slightly depend on the post-Newtonian order in the tidal phase and an increase in the tidal post-Newtonian order does not lead to a monotonic change in the estimate of. We also compare the estimate of obtained by the post-Newtonian tidal model and numerical-relativity calibrated tidal models. We find that the post-Newtonian model gives slightly larger estimate of and wider posterior distribution than the numerical-relativity calibrated models. According to Bayesian model comparison, it is difficult to identify a preference among the post-Newtonian orders by relying on the GW170817 and GW190425 data. Our results indicate no preference among numerical-relativity calibrated tidal models over the post-Newtonian model. Additionally, we present constraints on equation-of-state models for neutron stars with the post-Newtonian model, which show that the GW170817 data disfavor less compact models, though they are slightly weaker constraints than the numerical-relativity calibrated tidal models.