Abstract
The gravitational wave event, GW190521, is the most massive binary black hole merger observed by ground-based gravitational wave observatories LIGO/Virgo to date. While the observed gravitational wave signal is mainly in the merger and ringdown phases, the inspiral gravitational wave signal of the GW190521-like binary will be more visible to space-based detectors in the low-frequency band. In addition, the ringdown gravitational wave signal will be louder in the next generation (3G) of ground-based detectors in the high-frequency band, displaying the great potential of multiband gravitational wave observations. In this paper, we explore the scientific potential of multiband observations of GW190521-like binaries with a milli-Hz gravitational wave observatory: LISA; a deci-Hz observatory: B-DECIGO; and (next generation of) hecto-Hz observatories: aLIGO and ET. In the case of quasicircular evolution, the triple-band observations of LISA, B-DECIGO, and ET will provide parameter estimation errors of the masses and spin amplitudes of component black holes at the level of order of 1–10%. This would allow consistency tests of general relativity in the strong field at an unparalleled precision, particularly with the “B-DECIGO + ET” observation. In the case of eccentric evolution, the multiband signal-to-noise ratio found in “B-DECIGO + ET” observation would be larger than 100 for a five-year observation prior to coalescence, even with high final eccentricities.
Highlights
Among gravitational wave (GW) events detected by LIGO and Virgo during O1, O2, and O3a runs [1,2], a binary black hole (BBH) merger, GW190521 [3,4], is one of the most striking discoveries
In the aLIGO case, due to the low signal-to-noise ratio (SNR) (= 10.8) the parameter estimation errors already go beyond the Schwarzschild limit at the 3σ level, and we cannot confirm whether the remnant object is a BH predicted by general relativity (GR) with the 5σ level
Our first result for the parameter estimation errors is displayed in Tables 2 and 3; the statistical errors of the binary’s mass parameters by benefit from having (B-)DECIGO observation will be ∼10−2, and the multiband observation with LISA, B-DECIGO, and ET will further improve them to a factor of 2, even allowing the statistical errors of component BH spins at the accuracy level of ∼10−1
Summary
Among gravitational wave (GW) events detected by LIGO and Virgo during O1, O2, and O3a runs [1,2], a binary black hole (BBH) merger, GW190521 [3,4], is one of the most striking discoveries. In the case of the quasicircular BBH scenario (which is most favored by the LIGO/Virgo analysis [3,4]), the coalescing time and the number of GW cycles at frequency f (in the observer frame) are estimated as: tc ∼ 1.3 (1 + z)−5/3. This indicates the lack of the GW signals from the sufficiently long inspiral phase. Throughout this paper, the binary parameters and GW frequencies measured in the source’s rest frame are denoted with the index ‘r’, explicitly distinguished from those in the observer frame
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