Archival inference for eccentric stellar-mass binary black holes in space-based gravitational wave observations

Space-based gravitational-wave observatories will detect the early inspiral of stellar-mass binary black holes and can track their eccentricity evolution. However, untargeted searches in the space band are computationally demanding and require relatively high detection thresholds (signal-to-noise ratio ∼15). Information from ground-based detections can significantly shrink the parameter space for space-band analyses and thereby substantially reduce the detection threshold. We present a Bayesian inference pipeline for ground-triggered archival space-band analyses that includes eccentricity. Using ground-informed priors, we demonstrate that with one year of LISA or TianQin data a GW190521-like source with signal-to-noise ratio ∼7 can be distinguished and tightly constrained. In this setup, space observations sharpened the redshifted chirp mass from 𝒪⁡(10−3)⁢𝑀⊙ to 𝒪⁡(10−5)⁢𝑀⊙, and constrain the eccentricity to 𝒪⁡(10−5) around the injected value 𝑒0.01  Hz =0.1. These results demonstrate that inference of eccentric stellar-mass binary black holes in noisy space-band data is practically feasible, supports an expanded yield of multiband detections, and strengthens prospects for future astrophysical and gravitational tests.