Abstract
We analyze the impact of a proposed tidal instability coupling $p$modes and $g$modes within neutron stars on GW170817. This nonresonant instability transfers energy from the orbit of the binary to internal modes of the stars, accelerating the gravitationalwave driven inspiral. We model the impact of this instability on the phasing of the gravitational wave signal using three parameters per star: an overall amplitude, a saturation frequency, and a spectral index. Incorporating these additional parameters, we compute the Bayes Factor ($\ln B^{pg}_{!pg}$) comparing our $p$$g$ model to a standard one. We find that the observed signal is consistent with waveform models that neglect $p$$g$ effects, with $\ln B^{pg}_{!pg} = 0.03^{+0.70}_{0.58}$ (maximum a posteriori and 90% credible region). By injecting simulated signals that do not include $p$$g$ effects and recovering them with the $p$$g$ model, we show that there is a $\simeq 50\%$ probability of obtaining similar $\ln B^{pg}_{!pg}$ even when $p$$g$ effects are absent. We find that the $p$$g$ amplitude for 1.4 $M_\odot$ neutron stars is constrained to $\lesssim \text{few}\times10^{7}$, with maxima a posteriori near $\sim 10^{7}$ and $p$$g$ saturation frequency $\sim 70\, \mathrm{Hz}$. This suggests that there are less than a few hundred excited modes, assuming they all saturate by wave breaking. For comparison, theoretical upper bounds suggest a $p$$g$ amplitude $\lesssim 10^{6}$ and $\lesssim 10^{3}$ modes saturating by wave breaking. Thus, the measured constraints only rule out extreme values of the $p$$g$ parameters. They also imply that the instability dissipates $\lesssim 10^{51}\, \mathrm{ergs}$ over the entire inspiral, i.e., less than a few percent of the energy radiated as gravitational waves.
Original language  English 

Article number  061104 
Journal  Physical Review Letters 
Volume  122 
DOIs  
Publication status  Published  13 Feb 2019 
Keywords
 astroph.HE
 RCUK
 STFC
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Data availability statement for 'Constraining the pmodegmode tidal instability with GW170817'.
Harry, I. (Creator), Keitel, D. (Creator), Lundgren, A. (Creator) & Nuttall, L. (Creator), American Physical Society, 13 Feb 2019
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