Upper limits on the isotropic gravitationalwave background from Advanced LIGO and Advanced Virgo's third observing run
Abstract
We report results of a search for an isotropic gravitationalwave background (GWB) using data from Advanced LIGO's and Advanced Virgo's third observing run (O3) combined with upper limits from the earlier O1 and O2 runs. Unlike in previous observing runs in the advanced detector era, we include Virgo in the search for the GWB. The results of the search are consistent with uncorrelated noise, and therefore we place upper limits on the strength of the GWB. We find that the dimensionless energy density Ω_{GW}≤5.8 ×10^{9} at the 95% credible level for a flat (frequencyindependent) GWB, using a prior which is uniform in the log of the strength of the GWB, with 99% of the sensitivity coming from the band 2076.6 Hz; Ω_{GW}(f )≤3.4 ×10^{9} at 25 Hz for a powerlaw GWB with a spectral index of 2 /3 (consistent with expectations for compact binary coalescences), in the band 2090.6 Hz; and Ω_{GW}(f )≤3.9 ×10^{10} at 25 Hz for a spectral index of 3, in the band 20291.6 Hz. These upper limits improve over our previous results by a factor of 6.0 for a flat GWB, 8.8 for a spectral index of 2 /3 , and 13.1 for a spectral index of 3. We also search for a GWB arising from scalar and vector modes, which are predicted by alternative theories of gravity; we do not find evidence of these, and place upper limits on the strength of GWBs with these polarizations. We demonstrate that there is no evidence of correlated noise of magnetic origin by performing a Bayesian analysis that allows for the presence of both a GWB and an effective magnetic background arising from geophysical Schumann resonances. We compare our upper limits to a fiducial model for the GWB from the merger of compact binaries, updating the model to use the most recent datadriven population inference from the systems detected during O3a. Finally, we combine our results with observations of individual mergers and show that, at design sensitivity, this joint approach may yield stronger constraints on the merger rate of binary black holes at z ≳2 than can be achieved with individually resolved mergers alone.
 Publication:

Physical Review D
 Pub Date:
 July 2021
 DOI:
 10.1103/PhysRevD.104.022004
 arXiv:
 arXiv:2101.12130
 Bibcode:
 2021PhRvD.104b2004A
 Keywords:

 General Relativity and Quantum Cosmology;
 Astrophysics  Cosmology and Nongalactic Astrophysics
 EPrint:
 25 pages, 7 figures, Abstract abridged for arxiv submission