Estimating astrophysical population properties using a multicomponent stochastic gravitational-wave background search

Federico De Lillo and Jishnu Suresh

Phys. Rev. D 109, 103013 – Published 9 May 2024

Abstract

The recent start of the fourth observing run of the LIGO-Virgo-KAGRA (LVK) Collaboration has reopened the hunt for gravitational-wave (GW) signals, with one compact-binary-coalescence (CBC) signal expected to be observed every few days. Among the signals that could be detected for the first time there is the stochastic gravitational-wave background (SGWB) from the superposition of unresolvable GW signals that cannot be detected individually. In fact, multiple SGWBs are likely to arise given the variety of sources, making it crucial to identify the dominant components and assess their origin. However, most search methods with ground-based detectors assume the presence of one SGWB component at a time, which could lead to biased results in estimating its spectral shape if multiple SGWBs exist. Therefore, a joint estimate of the components is necessary. In this work, we adapt such an approach and analyze the data from the first three LVK observing runs, searching for a multicomponent isotropic SGWB. We do not find evidence for any SGWB and establish upper limits on the dimensionless energy parameter $Ω_{gw} (f)$ at 25 Hz for five different power-law spectral indices, $α = 0, 2 / 3$ , 2, 3, 4, jointly. For the spectral indices $α = 2 / 3$ , 2, 4, corresponding to astrophysical SGWBs from CBCs, r-mode instabilities in young rotating neutron stars, and magnetars, we draw further astrophysical implications by constraining the ensemble parameters $K_{CBC}, K_{r - modes}, K_{magnetars}$ , defined in the main text.

Received 16 October 2023
Accepted 25 March 2024

DOI:https://doi.org/10.1103/PhysRevD.109.103013

Physics Subject Headings (PhySH)

Gravitation Gravitational wave sources Gravitational waves

Gravitation, Cosmology & Astrophysics

Authors & Affiliations

Federico De Lillo ^* and Jishnu Suresh ^†

Centre for Cosmology, Particle Physics and Phenomenology (CP3), Université catholique de Louvain, Louvain-la-Neuve, B-1348, Belgium

^*federico.delillo@uclouvain.be
^†jishnu.suresh@uclouvain.be

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Vol. 109, Iss. 10 — 15 May 2024

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Images

Figure 1
Landscape plot with the intensity of different astrophysical SGWBs. The black line denotes the median value of the total CBC SGWB as inferred from the GWTC-3 in [8]. The blue line represents the median value of the BNS SGWB, again from [8]. The orange line is the SGWB from r modes from [20] with our conventions, setting $K = - 5 / 4$ and further scaling Eq. (17) to the case where just 1% of the young NSs enters the instability [61]. The purple line is the SGWB from magnetars, using $ϵ = 5 \times 10^{- 4}$ and $B = 10^{11} T$ , with the other parameters from [63].
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Figure 2
Preconditioned Fisher matrix for data from the first three LVK observing runs, showing the couplings among different spectral indices. The diagonal is unity by construction, with the off diagonal element being smaller than 1 and positive.
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Figure 3
Results of the parameter estimation for the $α = 2 / 3$ , 2, 4 combination in the 20–100 Hz band for power-law $Ω_{α}$ (left panel) and the corresponding astrophysical parameters (right panel). Contour plots show the $1 σ$ , $2 σ$ , and $3 σ$ credible areas (black, gray, light gray, respectively). The dashed black lines in the histogram panels delimit the $1 σ$ region of the estimated parameters.
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Figure 4
Parameter estimation results for the set of the power-law injections in the 20–1726 Hz frequency range, with $Ω_{α} = 1 \times 10^{- 6}$ , $α = 0, 2 / 3$ , 2, 3, 4, for the signal-only case (left panel) and on top of O3 data (right panel). Contour plots show the $1 σ$ , $2 σ$ , and $3 σ$ credible areas (black, gray, light gray, respectively). The red lines denote the injected values, while the yellow error bars represent the $1 σ$ uncertainty of the $Ω_{α}$ estimators from the joint analysis. The dashed black lines in the histogram panels delimit the $1 σ$ region of the estimated parameters.
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Figure 5
Parameter estimation results for $α = 2 / 3$ , 2, 4 from the two sets of the power-law injections in the 20–1726 Hz frequency range, with $Ω_{2} = 10^{- 3} \times Ω_{2 / 3}$ , $Ω_{4} = 10^{- 5} \times Ω_{2 / 3}$ , for the signal-only ( $Ω_{2 / 3} = 10^{- 9}$ , left) and the on-top-of-O3-data ( $Ω_{2 / 3} = 10^{- 4}$ , right) injections. Contour plots show the $1 σ$ , $2 σ$ , and $3 σ$ credible areas (black, gray, light gray, respectively). The red lines denote the injected values, while the yellow error bars represent the $1 σ$ uncertainty of the $Ω_{α}$ estimators from the joint analysis. The dashed black lines in the histogram panels delimit the $1 σ$ region of the estimated parameters.
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Figure 6
Results of the parameter estimation for the $α = 2 / 3$ , 2, 4 combination in the 20–100 Hz band for the astrophysical injection for BNS, r modes, and magnetar SGWBs (top row: signal-only injection; bottom row: injection on top of O3 data). The left panel shows the recovery of the $Ω_{α}$ , while the right panel the injected ensemble parameters. Contour plots show the $1 σ$ , $2 σ$ , and $3 σ$ credible areas (black, gray, light gray, respectively). The red lines denote the injected values, while the yellow error bars represent the $1 σ$ uncertainty of the $Ω_{α}$ estimators from the joint analysis. The dashed black lines in the histogram panels delimit the $1 σ$ region of the estimated parameters.
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