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We revisit the recent debate on the evidence for an overtone in the blackhole ringdown of GW150914 using an independent data-analysis pipeline. Bygating and inpainting the data, we discard the contamination from earlier partsof the gravitational wave signal before ringdown. This enables parameterestimation to be conducted in the frequency domain, which is mathematicallyequivalent to the time domain method. We keep the settings as similar aspossible to the previous studies by Cotesta et al. arXiv:2201.00822 and Isi etal. arXiv:1905.00869 arXiv:2202.02941 which yielded conflicting results on theBayes factor of the overtone. Our aim is to understand how different dataanalysis systematics, including sampling rates, erroneous timestamps, thefrequency resolution of the noise power spectrum, and the parameterization ofringdown amplitudes, would influence the statistical significance of anovertone. Our main results indicate the following: (i) a low-resolutionestimation of the noise power spectrum tends to diminish the significance ofovertones, (ii) adjusting the start time to a later digitized point reduces thesignificance of overtones, and (iii) overtone evidence varies with differentsampling rates if the start time is too early, indicating that the overtone isa poor model, hence we propose a convergence test to verify the validity of anovertone model. With these issues addressed, we find the Bayes factors for theovertone to range from $10$ to $26$ in a range of times centered at thebest-fit merger time of GW150914, which supports the existence of an overtonein agreement with the conclusions of Isi et al. arXiv:1905.00869arXiv:2202.02941.

A gating-and-inpainting perspective on GW150914 ringdown overtone: understanding the data analysis systematics