Paper published by B. P. Abbott et al. (LIGO Scientific Collaboration and Virgo Collaboration) at the Physical Review Letters.

Constraining the p -Mode– g -Mode Tidal Instability with GW170817

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 gravitational-wave 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 $p\text{−}g$ model to a standard one. We find that the observed signal is consistent with waveform models that neglect $p\text{−}g$ effects, with $\ln B_{!pg}^{pg}=0.03_{-0.58}^{+0.70}$ (maximum a posteriori and 90% credible region). By injecting simulated signals that do not include $p\text{−}g$ effects and recovering them with the $p\text{−}g$ model, we show that there is a $\simeq 50\%$ probability of obtaining similar $\ln B_{!pg}^{pg}$ even when $p\text{−}g$ effects are absent. We find that the $p\text{−}g$ amplitude for $1.4M_{\odot }$ neutron stars is constrained to less than a few tenths of the theoretical maximum, with maxima a posteriori near one-tenth this maximum and $p\text{−}g$ 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 $\lesssim {10}^3$ modes saturate by wave breaking. Thus, the measured constraints only rule out extreme values of the $p\text{−}g$ parameters. They also imply that the instability dissipates $\lesssim 10^{51}\mathrm{erg}$ over the entire inspiral, i.e., less than a few percent of the energy radiated as gravitational waves.

Image. Upper limits on the cumulative energy dissipated by the $p\text{−}g$ instability as a function of frequency. We note the relatively strong constraints at lower frequencies where $p\text{−}g$ effects are more pronounced.

Paper link available below at citation information

Citation:

B. P. Abbott et al. (LIGO Scientific Collaboration and Virgo Collaboration)
Constraining the p -Mode– g -Mode Tidal Instability with GW170817
Phys. Rev. Lett. 122, 061104
DOI: https://doi.org/10.1103/PhysRevLett.122.061104
13 February 2019