Abstract
An evolving Japanese gravitational-wave (GW) mission in the deci-Hz band: B-DECIGO (DECihertz laser Interferometer Gravitational wave Observatory) will enable us to detect GW150914-like binary black holes, GW170817-like binary neutron stars, and intermediate-mass binary black holes out to cosmological distances. The B-DECIGO band slots in between the aLIGO-Virgo-KAGRA-IndIGO (hecto-Hz) and LISA (milli-Hz) bands for broader bandwidth; the sources described emit GWs for weeks to years across the multiband to accumulate high signal-to-noise ratios. This suggests the possibility that joint detection would greatly improve the parameter estimation of the binaries. We examine B-DECIGO's ability to measure binary parameters and assess to what extent multiband analysis could improve such measurement. Using non-precessing post-Newtonian waveforms with the Fisher matrix approach, we find for systems like GW150914 and GW170817 that B-DECIGO can measure the mass ratio to within $< 0.1\%$, the individual black-hole spins to within $< 10\%$, and the coalescence time to within $< 5\,$s about a week before alerting aLIGO and electromagnetic facilities. Prior information from B-DECIGO for aLIGO can further reduce the uncertainty in the measurement of, e.g., certain neutron star tidally-induced deformations by factor of $\sim 6$, and potentially determine the spin-induced neutron star quadrupole moment. Joint LISA and B-DECIGO measurement will also be able to recover the masses and spins of intermediate-mass binary black holes at percent-level precision. However, there will be a large systematic bias in these results due to post-Newtonian approximation of exact GW signals.
Highlights
Similar to the electromagnetic spectrum, gravitational waves (GWs) have a gravitational spectrum that covers frequencies of GWs ranging from 10−8 Hz to 103 Hz, broadly divided into the four bands: nano-Hz, milli-Hz, deci-Hz and hecto-Hz
This suggests the interesting possibility that we may be able to precisely measure, for instance, individual BH spins in GW150914-like binary black holes (BBHs) in the B-DECIGO band, which can be hard to measure in the Advanced LIGO (aLIGO) band because of their strong degeneracy in the parameter dependence of the PN waveform [63,64,65,66,67,68]
We stress that the methodology of our analysis is extremely simplified, e.g., with a flat prior and by using only the inspiral-only PN waveform; our aLIGO estimation errors for System A (“GW170817”) and System B (“GW150914”) obviously contradict those measured by aLIGO and advanced Virgo [8, 13]
Summary
Similar to the electromagnetic spectrum, gravitational waves (GWs) have a gravitational spectrum that covers frequencies of GWs ranging from 10−8 Hz to 103 Hz, broadly divided into the four bands: nano-Hz, milli-Hz, deci-Hz and hecto-Hz. It is realized that LISA will be able to measure GW150914-like BBHs up to some thousands of them in the low-redshift universe [36, 37] Such measurement will accurately determine their sky position for aLIGO [36], distinguish their formation channels [38,39,40,41], and provide a new class of cosmological standard sirens [42, 43]. We shall assess how precisely we are able to measure the parameters of BNS and BBH inspirals with BDECIGO, and explore how multiband B-DECIGO and aLIGO/ET (or LISA) measurement improves their parameter estimation and science cases over those using only single-band detection. Some previous studies of parameter estimation in the DECIGO mission can be found in Refs. [30, 44, 48, 52,53,54]
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