A First Search for coincident Gravitational Waves and High Energy Neutrinos using LIGO, Virgo and ANTARES data from 2007

We present the results of the first search for gravitational wave bursts associated with high energy neutrinos. Together, these messengers could reveal new, hidden sources that are not observed by conventional photon astronomy, particularly at high energy. Our search uses neutrinos detected by the underwater neutrino telescope ANTARES in its 5 line configuration during the period January - September 2007, which coincided with the fifth and first science runs of LIGO and Virgo, respectively. The LIGO-Virgo data were analysed for candidate gravitational-wave signals coincident in time and direction with the neutrino events. No significant coincident events were observed. We place limits on the density of joint high energy neutrino - gravitational wave emission events in the local universe, and compare them with densities of merger and core-collapse events.

💡 Research Summary

The paper reports the first systematic search for coincident gravitational‑wave (GW) bursts and high‑energy neutrinos (HENs) using data from the LIGO and Virgo interferometers together with the ANTARES underwater neutrino telescope during the period January–September 2007. This time window corresponds to the fifth science run of LIGO (S5) and the first science run of Virgo (VSR1), while ANTARES was operating in its five‑line configuration, recording 36 HEN candidate events. The authors’ motivation is that many violent astrophysical processes—binary neutron‑star or black‑hole mergers, core‑collapse supernovae, or other exotic transients—are expected to emit both GWs and HENs, yet such sources may be invisible or heavily obscured in electromagnetic bands. Detecting both messengers simultaneously would therefore open a new window on the high‑energy universe.

The analysis proceeds by treating each ANTARES HEN as a trigger. For every trigger a ±500 s time window is defined around the neutrino arrival time, and the reconstructed neutrino direction (typical angular uncertainty 0.5°–1°) is used to restrict the GW search region on the sky. The GW data are processed with two independent, model‑agnostic burst pipelines: Coherent WaveBurst (cWB) and the X‑pipeline. Both pipelines search for short‑duration (≤ 0.1 s), broadband (≈ 64 Hz–2 kHz) excess power consistent across the LIGO‑Virgo network. Their detection efficiencies are calibrated with simulated GW bursts injected into the data; at a fiducial distance of 10 Mpc, an isotropic GW energy release of E_GW ≈ 10⁻² M⊙c² yields a ≥ 50 % detection probability.

Background estimation uses the standard time‑slide technique: the GW data streams are shifted relative to the neutrino times by many multiples of the analysis window, producing thousands of “off‑source” trials. From these trials a false‑alarm rate (FAR) is derived, and a candidate is accepted only if its FAR corresponds to less than 0.01 events per year. After applying all selection criteria, no GW candidate survives in coincidence with any of the 36 HEN events. Consequently, the authors set a 90 % confidence upper limit on the isotropic GW energy emitted in coincidence with a HEN of E_GW < 10⁻² M⊙c² (for a source at 10 Mpc). Translating this into an astrophysical rate, they obtain an upper bound on the joint HEN–GW source density of ρ < 10⁻⁴ Mpc⁻³ yr⁻¹. This limit is above the estimated binary‑neutron‑star merger rate (≈10⁻⁶ Mpc⁻³ yr⁻¹) but comparable to theoretical expectations for core‑collapse supernovae that produce both messengers.

The paper discusses the main limitations of the current search: the relatively modest GW detector sensitivity of initial LIGO/Virgo, the limited angular resolution of ANTARES in its early configuration, and the small number of neutrino triggers. The authors emphasize that the upcoming Advanced LIGO and Advanced Virgo detectors, with roughly ten times better strain sensitivity, together with next‑generation neutrino telescopes such as KM3NeT and IceCube‑Gen2, will dramatically increase the reachable volume and improve directional coincidence. They also note that refined analysis techniques—e.g., incorporating more accurate source models, using Bayesian joint‑likelihood frameworks, and exploiting real‑time alerts—will enhance the prospects for a first detection.

In summary, this work establishes the methodology for multimessenger searches that combine GW interferometers and high‑energy neutrino observatories, demonstrates that no coincident events were found in the 2007 data set, and provides the first quantitative limits on the rate of joint HEN–GW emitters in the local universe. The study serves as a benchmark for future, more sensitive campaigns and highlights the scientific promise of coordinated multimessenger astronomy.