Spin wandering of an accreting neutron star near torque balance: implications for gravitational wave searches
Abstract
Torque balance between gravitational radiation reaction and magnetocentrifugal accretion is one reason why accreting neutron stars rotate slower than centrifugal break-up. Random processes in the accretion disk, such as Rayleigh-Taylor instabilities and flicker noise, drive the spin frequency f∗ and gravitational wave frequency fgw∝ f∗ to wander stochastically around their torque balance values. Here it is shown theoretically, in terms of an idealized Ornstein-Uhlenbeck model, that the standard deviation of fgw is given by σfgw(h0) ∝ fgw h0 D βT1/2, or equivalently σfgw(FX) ∝ fgw1/2 FX1/2 D βT1/2, where h0 is the characteristic wave strain, FX is the X-ray flux, D is the source distance, and β and T are the fractional amplitude and autocorrelation time-scale of the stochastic torque. One can use σfgw(h0) and σfgw(FX) to check the physical consistency of a detection candidate in a gravitational wave search by comparing with σfgw observed. Spin wandering impacts search design, because it sets the maximum time interval max(Tcoh), during which the signal may be treated as coherent. The Ornstein-Uhlenbeck calculation predicts 10−1 ≲ max(Tcoh) / (1 day) ≲ 103, with 3× 10−2 ≲ βT1/2 / (1 s1/2 ) ≲ 4, for Rayleigh-Taylor instabilities and flicker noise. The predicted max(Tcoh) is shorter typically than the year-long observation runs of audio-band interferometers operating today, emphasizing the utility of semi-coherent search algorithms, which divide the data into multiple coherent segments of duration max(Tcoh).
Related
- Cosmological and High-Energy Physics Implications from Gravitational-Wave Background Searches in LIGO-Virgo-KAGRA’s O1–O4a Runs
- Effects of Rotation on the Gravitational Momentum Transfer in Neutron-Star Kicks and Implications for Spin-Kick Alignment
- Population synthesis of low-mass binaries with wind-accreting neutron stars
- Transient discs around isolated accreting neutron stars
- Accreting Neutron Stars in Low-Mass X-ray Binaries
BibTeX
@misc{melatos2026spin,
title = {{Spin wandering of an accreting neutron star near torque balance: implications for gravitational wave searches}},
author = {Andrew Melatos},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.32164},
eprint = {2609.32164},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.32164},
}
RIS
TY - UNPB
TI - Spin wandering of an accreting neutron star near torque balance: implications for gravitational wave searches
AU - Andrew Melatos
PY - 2026
DA - 2026/09/26
PB - arXiv
DO - 10.48550/arxiv.2609.32164
UR - https://arxiv.org/abs/2609.32164
AB - Torque balance between gravitational radiation reaction and magnetocentrifugal accretion is one reason why accreting neutron stars rotate slower than centrifugal break-up. Random processes in the accretion disk, such as Rayleigh-Taylor instabilities and flicker noise, drive the spin frequency f_∗ and gravitational wave frequency f_gw∝ f_∗ to wander stochastically around their torque balance values. Here it is shown theoretically, in terms of an idealized Ornstein-Uhlenbeck model, that the standard deviation of f_gw is given by σ_f_gw(h_0) ∝ f_gw h_0 D βT^1/2, or equivalently σ_f_gw(F_X) ∝ f_gw^1/2 F_X^1/2 D βT^1/2, where h_0 is the characteristic wave strain, F_X is the X-ray flux, D is the source distance, and β and T are the fractional amplitude and autocorrelation time-scale of the stochastic torque. One can use σ_f_gw(h_0) and σ_f_gw(F_X) to check the physical consistency of a detection candidate in a gravitational wave search by comparing with σ_f_gw observed. Spin wandering impacts search design, because it sets the maximum time interval max(T_coh), during which the signal may be treated as coherent. The Ornstein-Uhlenbeck calculation predicts 10^−1 ≲ max(T_coh) / (1 day) ≲ 10^3, with 3× 10^−2 ≲ βT^1/2 / (1 s^1/2 ) ≲ 4, for Rayleigh-Taylor instabilities and flicker noise. The predicted max(T_coh) is shorter typically than the year-long observation runs of audio-band interferometers operating today, emphasizing the utility of semi-coherent search algorithms, which divide the data into multiple coherent segments of duration max(T_coh).
ER -