Stochastic gravitational-wave background searches and constraints on neutron-star ellipticity

Abstract

Rotating neutron stars (NSs) are promising sources of gravitational waves (GWs) in the frequency band of ground-based detectors. They are expected to emit quasi-monochromatic, long-duration GW signals, called continuous waves (CWs), due to their deviations from spherical symmetry. The degree of such deformations, and hence the information about the internal structure of a NS, is encoded in a dimensionless parameter $\epsilon$ called ellipticity. Searches for CW signals from isolated Galactic NSs have shown to be sensitive to ellipticities as low as $\epsilon \sim \mathcal{O}(10^{-9})$. These searches are optimal for detecting and characterising GWs from individual NSs, but they are not designed to measure the properties of NSs as population, such as the average ellipticity ${\epsilon }_{\mathrm{av}}$. These ensemble properties can be determined by the measurement of the stochastic gravitational-wave background (SGWB) arising from the superposition of GW signals from individually-undetectable NSs. In this work, we perform a cross-correlation search for such a SGWB using the data from the first three observation runs of Advanced LIGO and Virgo. Finding no evidence for a SGWB signal, we set upper limits on the dimensionless energy density parameter ${\Omega }_{\mathrm{gw}}(f)$. Using these results, we also constrain the average ellipticity of Galactic NSs and five NS ``hotspots'', as a function of the number of NSs emitting GWs within the frequency band of the search $N_{\mathrm{band}}$. We find ${\epsilon }_{\mathrm{av}}\lesssim 1.8\times 10^{-8}$, with $N_{\mathrm{band}}=1.6\times 10^7$, for Galactic NSs, and ${\epsilon }_{\mathrm{av}}\lesssim [3.5-11.8]\times 10^{-7}$, with $N_{\mathrm{band}}=1.6\times 10^{10}$, for NS hotspots.

10 pages, 6 figures, 2 tables

References in corpus (17)

• Advanced Virgo: a 2nd generation interferometric gravitational wave detector
• Advanced LIGO
• Improved Calculation of the Primordial Gravitational Wave Spectrum in the Standard Model
• Search for post-merger gravitational waves from the remnant of the binary neutron star merger GW170817
• Recent searches for continuous gravitational waves
• Upper limit map of a background of gravitational waves
• Population synthesis of radio and gamma-ray millisecond pulsars from the Galactic disk
• Gravitational wave radiometry: Mapping a stochastic gravitational wave background
• All-sky Search for Continuous Gravitational Waves from Isolated Neutron Stars in the Early O3 LIGO Data
• Search methods for continuous gravitational-wave signals from unknown sources in the advanced-detector era
• Gravitational wave background from rotating neutron stars
• Measuring neutron-star ellipticity with measurements of the stochastic gravitational-wave background
• A synthetic model of the gravitational wave background from evolving binary compact objects
• The Adaptive Transient Hough method for long-duration gravitational wave transients
• Loosely coherent search in LIGO O1 data for continuous gravitational waves from Terzan 5 and the galactic center
• Search strategies for long gravitational-wave transients: hidden Markov model tracking and seedless clustering
• Method to detect gravitational waves from an ensemble of known pulsars