Effects of waveform model systematics on the interpretation of GW150914

Abstract

Parameter estimates of GW150914 were obtained using Bayesian inference, based on three semi-analytic waveform models for binary black hole coalescences. These waveform models differ from each other in their treatment of black hole spins, and all three models make some simplifying assumptions, notably to neglect sub-dominant waveform harmonic modes and orbital eccentricity. Furthermore, while the models are calibrated to agree with waveforms obtained by full numerical solutions of Einstein's equations, any such calibration is accurate only to some non-zero tolerance and is limited by the accuracy of the underlying phenomenology, availability, quality, and parameter-space coverage of numerical simulations. This paper complements the original analyses of GW150914 with an investigation of the effects of possible systematic errors in the waveform models on estimates of its source parameters. To test for systematic errors we repeat the original Bayesian analyses on mock signals from numerical simulations of a series of binary configurations with parameters similar to those found for GW150914. Overall, we find no evidence for a systematic bias relative to the statistical error of the original parameter recovery of GW150914 due to modeling approximations or modeling inaccuracies. However, parameter biases are found to occur for some configurations disfavored by the data of GW150914: for binaries inclined edge-on to the detector over a small range of choices of polarization angles, and also for eccentricities greater than ∼0.05. For signals with higher signal-to-noise ratio than GW150914, or in other regions of the binary parameter space (lower masses, larger mass ratios, or higher spins), we expect that systematic errors in current waveform models may impact gravitational-wave measurements, making more accurate models desirable for future observations.

Distinguishing spin-aligned and isotropic black hole populations with gravitational waves

“…The effect of these approximations on inference on the parameters describing GW150914 has been investigated in detail 39 . For this source, statistical uncertainties dominate over any waveform systematics.…”

“…Detailed comparisons with numerical relativity computations using no approximations to the dynamics 40 also suggest that statistical uncertainties dominate the systematics for this system. Systematics may dominate for signals with such a large signal-to-noise ratio (approximately 23) when the source is edge-on or has high spins 39 . The other two events discussed here have much lower signal-to-noise ratios, with correspondingly larger statistical uncertainties, and are probably similarly oriented and with similarly small spins, so we do not expect systematic uncertainties to dominate.…”

Systematic challenges for future gravitational wave measurements of precessing binary black holes

“…Extending the study of Ref. [46], which focused on weakly precessing systems, we show that inferences about GW sources derived using the conventional configuration can frequently be biased, particularly in certain regions of the parameter space and about observationally relevant pairs of parameters. We show that the conclusions reached can be strongly dependent on the model used.…”

Accurate inspiral-merger-ringdown gravitational waveforms for nonspinning black-hole binaries including the effect of subdominant modes

“…Most of these waveform families aim to model only the leading (quadrupole; l ¼ 2; m ¼ AE2) modes of the gravitational radiation. Indeed, careful investigations suggest that the systematic errors introduced by neglecting subdominant (nonquadrupole) modes in the parameter estimation of the LIGO events are negligible [26]. Due to the near "face-on" orientations of the binaries and moderate mass ratios, the effect of subdominant modes was negligible in the observed signals-the systematic errors introduced by neglecting the subdominant modes were well within the statistical errors [26].…”

“…Indeed, careful investigations suggest that the systematic errors introduced by neglecting subdominant (nonquadrupole) modes in the parameter estimation of the LIGO events are negligible [26]. Due to the near "face-on" orientations of the binaries and moderate mass ratios, the effect of subdominant modes was negligible in the observed signals-the systematic errors introduced by neglecting the subdominant modes were well within the statistical errors [26]. However, for binaries with large mass ratios or high inclination angles or large signal-to-noise ratios, the systematic errors can dominate the statistical errors, biasing our inference of the physical and astrophysical properties of the source (see, e.g., [27][28][29]).…”