Accuracy in measuring the neutron star mass in the gravitational wave parameter estimation for black hole-neutron star binaries

Recently, two gravitational wave (GW) signals, named as GW150914 and GW151226, have been detected by the two LIGO detectors. Although both signals were identified as originating from merging black hole (BH) binaries, GWs from systems containing neutron stars (NSs) are also expected to be detected in the near future by the advanced detector network. In this work, we assess the accuracy in measuring the NS mass ( M NS ) for the GWs from BH-NS binaries adopting the Advanced LIGO sensitivity with a signal-to-noise ratio of 10. By using the Fisher matrix method, we calculate the measurement errors ( σ ) in M NS assuming a NS mass of 1 ≤ M NS / M ⊙ ≤ 2 and low-mass BHs with masses in the range of 4 ≤ M BH / M ⊙ ≤ 10. We use the TaylorF2 waveform model in which the spins are aligned with the orbital angular momentum, but here we only consider the BH spins. We find that the fractional errors ( σ / M NS × 100) are in the range of 10% − 50% in our mass region for a given dimensionless BH spin χ BH = 0. The errors tend to increase as the BH spin increases, and this tendency is stronger for higher NS masses (or higher total masses). In particular, for the highest mass NSs ( M NS = 2 M ⊙ ), the errors σ can be larger than the true value of M NS if the dimensionless BH spin exceeds ~ 0.6.