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#### On the properties of the massive binary black hole merger GW170729

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1903.06742.pdf

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##### Citation

Chatziioannou, K., Cotesta, R., Ghonge, S., Lange, J., Ng, K.-K.-.-Y., Bustillo, J. C., et al. (2019).
On the properties of the massive binary black hole merger GW170729.* Physical Review D,*
*100*(10): 104015. doi:10.1103/PhysRevD.100.104015.

Cite as: https://hdl.handle.net/21.11116/0000-0003-5466-C

##### Abstract

We present a detailed investigation into the properties of GW170729, the

gravitational wave with the most massive and distant source confirmed to date.

We employ an extensive set of waveform models, including new improved models

that incorporate the effect of higher-order waveform modes which are

particularly important for massive systems. We find no indication of

spin-precession, but the inclusion of higher-order modes in the models results

in an improved estimate for the mass ratio of $(0.3-0.8)$ at the 90\% credible

level. Our updated measurement excludes equal masses at that level. We also

find that models with higher-order modes lead to the data being more consistent

with a smaller effective spin, with the probability that the effective spin is

greater than zero being reduced from $99\%$ to $94\%$. The 90\% credible

interval for the effective spin parameter is now $(-0.01-0.50)$. Additionally,

the recovered signal-to-noise ratio increases by $\sim0.3$ units compared to

analyses without higher-order modes. We study the effect of common spin priors

on the derived spin and mass measurements, and observe small shifts in the

spins, while the masses remain unaffected. We argue that our conclusions are

robust against systematic errors in the waveform models. We also compare the

above waveform-based analysis which employs compact-binary waveform models to a

more flexible wavelet- and chirplet-based analysis. We find consistency between

the two, with overlaps of $\sim 0.9$, typical of what is expected from

simulations of signals similar to GW170729, confirming that the data are

well-described by the existing waveform models. Finally, we study the

possibility that the primary component of GW170729 was the remnant of a past

merger of two black holes and find this scenario to be indistinguishable from

the standard formation scenario.

gravitational wave with the most massive and distant source confirmed to date.

We employ an extensive set of waveform models, including new improved models

that incorporate the effect of higher-order waveform modes which are

particularly important for massive systems. We find no indication of

spin-precession, but the inclusion of higher-order modes in the models results

in an improved estimate for the mass ratio of $(0.3-0.8)$ at the 90\% credible

level. Our updated measurement excludes equal masses at that level. We also

find that models with higher-order modes lead to the data being more consistent

with a smaller effective spin, with the probability that the effective spin is

greater than zero being reduced from $99\%$ to $94\%$. The 90\% credible

interval for the effective spin parameter is now $(-0.01-0.50)$. Additionally,

the recovered signal-to-noise ratio increases by $\sim0.3$ units compared to

analyses without higher-order modes. We study the effect of common spin priors

on the derived spin and mass measurements, and observe small shifts in the

spins, while the masses remain unaffected. We argue that our conclusions are

robust against systematic errors in the waveform models. We also compare the

above waveform-based analysis which employs compact-binary waveform models to a

more flexible wavelet- and chirplet-based analysis. We find consistency between

the two, with overlaps of $\sim 0.9$, typical of what is expected from

simulations of signals similar to GW170729, confirming that the data are

well-described by the existing waveform models. Finally, we study the

possibility that the primary component of GW170729 was the remnant of a past

merger of two black holes and find this scenario to be indistinguishable from

the standard formation scenario.