Inspiraling supermassive black hole binary systems with high orbitaleccentricity are important sources for space-based gravitational wave (GW)observatories like the Laser Interferometer Space Antenna (LISA). Eccentricityadds orbital harmonics to the Fourier transform of the GW signal andrelativistic pericenter precession leads to a three-way splitting of eachharmonic peak. We study the parameter estimation accuracy for such waveformswith different initial eccentricity using the Fisher matrix method and a MonteCarlo sampling of the initial binary orientation. The eccentricity improves theparameter estimation by breaking degeneracies between different parameters. Inparticular, we find that the source localization precision improvessignificantly for higher-mass binaries due to eccentricity. The typical skyposition errors are $\sim1 $deg for a nonspinning, $10^7\,M_{\odot}$ equal-massbinary at redshift $z=1$, if the initial eccentricity 1 yr before merger is$e_0\sim 0.6$. Pericenter precession does not affect the source localizationaccuracy significantly, but it does further improve the mass and eccentricityestimation accuracy systematically by a factor of 3--10 for masses between$10^6$ and $10^7\,M_{\odot}$ for $e_0 \sim 0.3$.
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