All-sky search for short gravitational-wave bursts in the second Advanced LIGO and Advanced Virgo run

B. P. Abbott et al. (LIGO Scientific Collaboration and Virgo Collaboration)

Phys. Rev. D 100, 024017 – Published 11 July 2019

Abstract

We present the results of a search for short-duration gravitational-wave transients in the data from the second observing run of Advanced LIGO and Advanced Virgo. We search for gravitational-wave transients with a duration of milliseconds to approximately one second in the 32–4096 Hz frequency band with minimal assumptions about the signal properties, thus targeting a wide variety of sources. We also perform a matched-filter search for gravitational-wave transients from cosmic string cusps for which the waveform is well modeled. The unmodeled search detected gravitational waves from several binary black hole mergers which have been identified by previous analyses. No other significant events have been found by either the unmodeled search or the cosmic string search. We thus present the search sensitivities for a variety of signal waveforms and report upper limits on the source rate density as a function of the characteristic frequency of the signal. These upper limits are a factor of 3 lower than the first observing run, with a 50% detection probability for gravitational-wave emissions with energies of $\sim 10^{- 9} M_{⊙} c^{2}$ at 153 Hz. For the search dedicated to cosmic string cusps we consider several loop distribution models, and present updated constraints from the same search done in the first observing run.

Received 9 May 2019

DOI:https://doi.org/10.1103/PhysRevD.100.024017

Physics Subject Headings (PhySH)

Gravitational wave detection Gravitational waves

Gravitational wave detectors

Gravitation, Cosmology & Astrophysics

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Vol. 100, Iss. 2 — 15 July 2019

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Images

Figure 1
Cumulative number of events versus inverse false-alarm rate found by the cWB search using all O2 data (circle points) and the cWB search where times around all compact binary coalescence sources (see Table I from Ref. [3]) have been dropped out (triangular points). The solid line shows the expected background, given the analysis time. The shaded regions show the 1, 2, and $3 σ$ Poisson uncertainty regions. Top: Search results from the cWB low-frequency (32–1024 Hz) band, with results grouped considering all the bins, applying a trials factor equal to 2. Bottom: Search results from the cWB high-frequency (1024–4096 Hz) band. No triggers associated with known BBH signals were found in this search.
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Figure 2
Cumulative number of events versus inverse false-alarm rate found by the oLIB search using all O2 data (circle points) and the oLIB search where times around all compact binary coalescence sources (see Table I from Ref. [3]) have been dropped out (triangular points). The solid line shows the expected background, given the analysis time. The shaded regions show the 1, 2, and $3 σ$ Poisson uncertainty regions. Top: The results of the low-frequency (32–1024 Hz) band. The low-frequency band contains two search bins—a high- $Q$ bin and a low- $Q$ bin—but as there were no foreground triggers in the low- $Q$ bin, only the high- $Q$ bin is represented here. Bottom: The search results for the high-frequency (1024–2048) band, which contains only a single search bin.
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Figure 3
Cumulative number of events versus inverse false-alarm rate found by the BW follow-up to the cWB low-frequency search using all O2 data (circle points) and the BW follow-up where times around all compact binary coalescence sources (see Table I from Ref. [3]) have been dropped out (triangular points). The solid line shows the expected background, given the analysis time. The shaded regions show the 1, 2, and $3 σ$ Poisson uncertainty regions.
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Figure 4
The GW emitted energy in units of solar masses that correspond to a 50% detection efficiency at an iFAR of 100 years, for a source emitting at 10 kpc. The waveforms represented here include all of the sine-Gaussian and white-noise burst injections as give in Table 1. We present the best sensitivity achieved by any of the unmodeled search pipelines, for both the O1 [20] and O2 searches.
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Figure 5
Upper limits on the 90% confidence intervals for the GW rate density, as measured in O2 using the SG and WNB waveforms listed in Table 1. Here we show the strictest upper limit achieved by any of the three unmodeled search pipelines. These results can be scaled to any emission energy $E_{GW}$ using the $rate density \propto E_{GW}^{- 3 / 2}$ . We also show the results from the O1 all-sky search [20], which presented results from the cWB pipeline for sine-Gaussian waveforms. Note that the O1 cWB search used three bins, which mostly affected the efficiency for waveforms belonging to $L F 1$ (i.e., 70 and 235 Hz, shown here as blue dots).
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Figure 6
Top: Cumulative event rate for the cosmic string search as a function of the ranking statistic $Λ$ (red points). The black line shows the expected background distribution with a $\pm 1 σ$ statistical error represented by the hatched area. The highest-ranked event ( $Λ_{h} ≃ 9.01$ ) is consistent with the background. Bottom: Search detection efficiency as a function of the cusp signal amplitude, when combining O1 and O2 LIGO data sets. This is measured by the fraction of simulated cusp events recovered with $Λ > Λ_{h}$ .
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