Detecting intermediate-mass black hole binaries with atom interferometer observatories: Using the resonant mode for the merger phase

Abstract: Atom interferometry detectors like AION, ZAIGA, and AEDGE will be able to detect gravitational waves (GWs) at dHz covering the band between large space-based laser interferometers LISA/TianQin/Taiji and ground-based facilities LIGO/Virgo/KAGRA. They will detect the late inspiral and merger of GW sources containing intermediate-mass black holes (IMBHs) in the mass range $10^2-10^5\,{\rm M_\odot}$. We study how accurately the parameters of an IMBH binary can be measured using the noise curve of AION. Furthermore, we propose a detection scheme where the early inspiral of the binary is detected using the regular broadband mode while the merger is detected using the resonant mode. We find that by using such a detection scheme the signal-to-noise ratio (SNR) of the detection as well as the detection accuracy of the parameters can be enhanced compared to the full detection of the signal using the broadband mode. We, further, assess the impact of the necessary detection gap while switching from broadband to resonant mode studying the case of a short ($30\,{\rm s}$) and a long ($600\,{\rm s}$) gap. We find that the improvement in SNR and detection accuracy is bigger for the shorter gap but that even in the case of the long gap such a scheme can be beneficial.