Search for anisotropic gravitational-wave backgrounds using data from Advanced LIGO and Advanced Virgo’s first three observing runs

Abstract

We report results from searches for anisotropic stochastic gravitational-wave backgrounds using data from the first three observing runs of the Advanced LIGO and Advanced Virgo detectors. For the first time, we include Virgo data in our analysis and run our search with a new efficient pipeline called PyStoch on data folded over one sidereal day. We use gravitational-wave radiometry (broadband and narrow band) to produce sky maps of stochastic gravitational-wave backgrounds and to search for gravitational waves from point sources. A spherical harmonic decomposition method is employed to look for gravitationalwave emission from spatially-extended sources. Neither technique found evidence of gravitational-wave signals. Hence we derive 95% confidence-level upper limit sky maps on the gravitational-wave energy flux from broadband point sources, ranging from F α;Θ < ð0.013-7.6Þ × 10 −8 erg cm −2 s −1 Hz −1 , and on the (normalized) gravitational-wave energy density spectrum from extended sources, ranging from Ω α;Θ < ð0.57-9.3Þ × 10 −9 sr −1 , depending on direction (Θ) and spectral index (α). These limits improve upon previous limits by factors of 2.9-3.5. We also set 95% confidence level upper limits on the frequencydependent strain amplitudes of quasimonochromatic gravitational waves coming from three interesting targets, Scorpius X-1, SN 1987A and the Galactic Center, with best upper limits range from h 0 < ð1.7-2.1Þ × 10 −25 , a factor of ≥ 2.0 improvement compared to previous stochastic radiometer searches.

Advanced Virgo: Status of the Detector, Latest Results and Future Prospects

“…Since the results of the search are consistent with uncorrelated noise, upper limits on the dimensionless energy density are reported, improving previous bounds by a factor of 6.0 for the flat background case. No evidence for gravitational waves in any of the three analyses in [207] looking for the anisotropic SGWB has been found. Hence, 95% confidence-level upper limits on the gravitational-wave energy density due to extended sources on the sky, on gravitationalwave energy flux from different directions on the sky, and on the median strain amplitude from possible sources in the directions of Scorpius X-1, the Galactic center, and SN 1987A are reported.…”

“…The synergy in this field is twofold: EM information is crucial to limit the parameter space to investigate but, on the other hand, the detection of GWs from a particularly interesting sky region, could be a trigger for astronomers for the observation of new populations of compact objects. In fact, a widely studied case, where this latter aspect is fundamental, is the search for GWs (mainly CW and stochastic) from the Galactic Center [37,207]. The detection of a GW emission from this region, if due to the presence of a pulsar population, can potentially solve the origin of the GeV excess measured by gamma-ray telescopes [208,209], debated to be due to dark matter around Sgr A* [210].…”

Stochastic Gravitational-Wave Backgrounds: Current Detection Efforts and Future Prospects

“…Although notably more challenging when attempting map-making with a singular F, the spectral dependence may be solved for as well, resulting in narrowband directional searches. These have been carried out by the LVK collaboration targeting point-like sources which may have an interesting spectral emission (e.g., asymmetric neutron stars, supernova remnants, the galactic bulge) and have been performed in pixel space [188,189,212]. As point sources are not correlated with other points on the sky, this type of search ignores the off-diagonal correlations in the Fisher matrix to avoid the inversion problem.…”

“…science run [229], followed by several other science runs of the LIGO detectors [16,[230][231][232], and the Advanced detector era since 2016 [162,233], and, finally, the inclusion of Virgo [56]. Beyond these, several other searches have been carried out by targeting specific GWBs; notably, searches which allow for anisotropy in the signal have regularly been carried out [212,[234][235][236][237], as well as searches for cosmic string networks [130,238,239]. Other targeted searches include searches for non-GR polarisation modes [56,162,240].…”

Alternative LISA-TAIJI networks

“…The detector network surrounding the Earth will improve the angular resolution of the sky localization and parameter determination on the GW sources [6,7]. Although the current GW detections are all from the compact binary coalescences, Advanced LIGO and Advanced Virgo are actively searching for the stochastic GW background (SGWB) [8][9][10][11][12][13]. The detection of the stochastic relic GW will deeply impact our understanding on the early Universe.…”