LIGO Document P1600048-v6

An improved analysis of GW150914 using a fully spin-precessing waveform model

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This paper presents updated estimates of source parameters for GW150914, a binary black-hole coalescence event detected by the Laser Interferometer Gravitational-wave Observatory (LIGO) on September 14, 2015 [1]. Reference presented parameter estimation [2] of the source using a 13-dimensional, phenomenological precessing-spin model (precessing {IMRPhenom}) and a 11-dimensional nonprecessing effective-one-body (EOB) model calibrated to numerical-relativity simulations, which forces spin alignment (nonprecessing EOBNR). Here we present new results that include a 15-dimensional precessing-spin waveform model (precessing EOBNR) developed within the EOB formalism. We find good agreement with the parameters estimated previously [2], and we quote updated component masses of $35^{+5}_{-3}$\ \Msun\ and $30^{+3}_{-4}$\ \Msun (where errors correspond to 90\% symmetric credible intervals).
We also present slightly tighter constraints on the dimensionless spin magnitudes of the two black holes, with a primary spin estimate $0.65$ and a secondary spin estimate $0.75$ at 90\% probability.
Reference [2] estimated the systematic parameter-extraction errors due to waveform-model uncertainty by combining the posterior probability densities of precessing {IMRPhenom} and nonprecessing EOBNR. Here
we find that the two precessing-spin models are in closer agreement, suggesting that these systematic errors are smaller than previously quoted.
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