Noise residuals for GW150914 using maximum likelihood and numerical relativity templates

We reexamine the results presented in [1] in which the properties of the noise residuals in the 40 ms chirp domain of GW150914 were investigated. This paper con firmed the presence of strong (i.e., about 0.80) correlations between residual noise in the Hanford and Livingston detectors in the chirp domain as previously seen by [2] when using a numerical relativity template given in [3]. It was also shown in [1] that a so-called maximum likelihood template can reduce these statistically significant cross-correlations. Here, we demonstrate that the reduction of correlation and statistical significance is due to (i) the use of a peculiar template with extreme spin (0.977), which is qualitatively different from the properties of GW150914 originally published by LIGO, (ii) a suspicious MCMC chain, (iii) uncertainties in the matching of the maximum likelihood (ML) template to the data in the Fourier domain, and (iv) a biased estimation of the significance that gives counterintuitive results. We show that rematching the maximum likelihood template to the data in the 0.2 s domain containing the GW150914 signal restores these correlations at the level of 60% of those found previously [1]. With necessary corrections, the probability given in [1] for the residual correlation will decrease by more than one order of magnitude. Since the ML template is itself problematic, results associated with it are illustrative rather than final.