Science with the TianQin observatory: Preliminary result on extreme-mass-ratio inspirals

Abstract

Systems consisting of a massive black hole and a stellar-origin compact object (CO), known as extreme-mass-ratio inspirals (EMRIs), are of great significance for space-based gravitational-wave detectors, as they will allow for testing gravitational theories in the strong field regime, and for checking the validity of the black hole no-hair theorem. In this work, we present a calculation of the EMRI rate and parameter estimation capabilities of the TianQin observatory, for various astrophysical models for these sources. We find that TianQin can observe EMRIs involving COs with a mass of $10\text{ }\text{ }{M}_{\ensuremath{\bigodot}}$ up to redshift $\ensuremath{\sim}2$. We also find that detections could reach tens or hundreds per year in the most optimistic astrophysical scenarios. Intrinsic parameters are expected to be recovered to within fractional errors of $\ensuremath{\sim}{10}^{\ensuremath{-}6}$, while typical errors on the luminosity distance and sky localization are 10% and $10\text{ }\text{ }{\mathrm{deg}}^{2}$, respectively. TianQin observation of EMRIs can also constrain possible deviations from the Kerr quadrupole moment to within fractional errors $\ensuremath{\lesssim}{10}^{\ensuremath{-}4}$. We also find that a network of multiple detectors would allow for improvements in both detection rates (by a factor $\ensuremath{\sim}1.5--3$) and in parameter estimation precision (20-fold improvement for the sky localization and fivefold improvement for the other parameters).