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All-sky search for continuous gravitational waves from isolated neutron stars using Advanced LIGO and Advanced Virgo O3 data

R. Abbott et al. (LIGO Scientific Collaboration, Virgo Collaboration, and KAGRA Collaboration)
Phys. Rev. D 106, 102008 – Published 28 November 2022
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  • INTRODUCTION
  • DATASETS USED
  • OVERVIEW OF SEARCH PIPELINES
  • DETAILS OF SEARCH METHODS
  • RESULTS
  • CONCLUSIONS
  • ACKNOWLEDGMENTS
  • APPENDICES
    • References

    Abstract

    We present results of an all-sky search for continuous gravitational waves which can be produced by spinning neutron stars with an asymmetry around their rotation axis, using data from the third observing run of the Advanced LIGO and Advanced Virgo detectors. Four different analysis methods are used to search in a gravitational-wave frequency band from 10 to 2048 Hz and a first frequency derivative from −10−8 to 10−9  Hz/s. No statistically significant periodic gravitational-wave signal is observed by any of the four searches. As a result, upper limits on the gravitational-wave strain amplitude h0 are calculated. The best upper limits are obtained in the frequency range of 100 to 200 Hz and they are ∼1.1×10−25 at 95% confidence level. The minimum upper limit of 1.10×10−25 is achieved at a frequency 111.5 Hz. We also place constraints on the rates and abundances of nearby planetary- and asteroid-mass primordial black holes that could give rise to continuous gravitational-wave signals.

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    • Received 3 January 2022
    • Accepted 17 October 2022

    DOI:https://doi.org/10.1103/PhysRevD.106.102008

    © 2022 American Physical Society

    Physics Subject Headings (PhySH)

    1. Research Areas
    Gravitational wave sources
    1. Physical Systems
    Neutron stars & pulsars
    1. Techniques
    Gravitational wave detection
    Gravitation, Cosmology & Astrophysics

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    Vol. 106, Iss. 10 — 15 November 2022

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    Images

    • Figure 1
      Figure 1

      Frequency and frequency derivative search ranges of the four pipelines: the FrequencyHough pipeline ranges marked in grey, SkyHough in red, Time-Domain F-statistic in blue, and SOAP in magenta. See Table 1 for details.

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    • Figure 2
      Figure 2

      Frequency time derivative for tentative emission of GWs (f˙≡2f˙rot) as a function of the frequency of emitted GWs (f≡2frot), where frot and f˙rot are rotational frequency and frequency time derivative for known pulsars, obtained from the Australia Telescope National Facility (ATNF) database [53]. The vertical axis shows the absolute value for both negative values of the frequency time derivative (“spin-down,” blue dots) and positive values (“spinup,” red plus symbols). Blue dashed lines represent spin-down limits used in the Time-Domain F-statistic search: for f<200  Hz, 0>f˙>−f/τmin, where τmin=1000  yr denotes a limit on pulsar’s characteristic age; for f>200  Hz, f˙>−2×10−10  Hz/s. For f>200  Hz in the case of spinning-up objects, in the F-statistic search we admit a positive range of values to f˙<2×10−11  Hz/s. The boundary of this range is marked by a red continuous line.

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    • Figure 3
      Figure 3

      Example sigmoid function fit (green solid line) to the injected data efficiencies (blue dots), representing the detection efficiency E as a function of injected GW amplitude h0 used in Time-Domain F-statistic search. Pale red and blue curves mark the 1σ confidence band obtained from the uncertainty of the fit. Red error bar marks the ±1σ standard deviation on the h095% value, corresponding to the efficiency of 0.95 (indicated by the horizontal dashed gray line). Vertical errors for each efficiency represent 1σ standard binomial errors related to detection rate, σE=E(1−E)/Ni, where E is the efficiency and Ni=100 is the number of injections for each GW amplitude. The data shown relates to the subband with the frequency of the lower edge of the band equal to 725.95 Hz.

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    • Figure 4
      Figure 4

      Peakmap of H1 (left) and L1 (right) data showing one of the eight outliers removed by veto V5 in the second follow-up step, see Table 6. All the eight outliers were generated by the hardware injection ip1. A Doppler correction, with parameters not exactly equal with those of the signal, nevertheless aligns some of the signal peaks, thus producing an excess of counts in the FrequencyHough map.

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    • Figure 5
      Figure 5

      O3 conservative upper limit estimation (bold continuous curve) and sensitivity lower bound (light dashed curve) for the FrequencyHough search.

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    • Figure 6
      Figure 6

      SkyHough candidates consistent with a broad spectral artifact in the H1 detector. Upper panel shows the cumulative semicoherent F-statistic using 660 coherent segments (Tcoh=0.5  days). Lower panel shows the segment-wise F-statistic. Dashed red line represents the single-detector F-statistic using H1-only data; the dot-dashed blue line represents the single-detector F-statistic using L1-only data. Solid gray line represents the multidetector F-statistic. Dotted horizontal line represents the threshold of 2F=3450 set at the initial follow-up stage.

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    • Figure 7
      Figure 7

      SkyHough candidate consistent with two narrow spectral artifacts of unknown origin in the H1 detector. The legend is equivalent to that of Fig. 6.

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    • Figure 8
      Figure 8

      SkyHough candidate consistent with a narrow spectral artifact of unknown origin in the H1 detector. The legend is equivalent to that of Fig. 6.

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    • Figure 9
      Figure 9

      ASD employed by the SkyHough pipeline to estimate the sensitivity of the search. ASD is computed as the square root of the single-sided inverse-square averaged PSD using data from both the H1 and L1 advanced LIGO detectors, as explained in the text surrounding Eq. (18).

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    • Figure 10
      Figure 10

      Example computation of D95% (white star) at a frequency band by fitting a sigmoid function (blue solid line) to a set of efficiencies (blue dots) computed using 200 injections at each sensitivity depth for the SkyHough search. Shaded regions represent 1, 2, and 3 sigma envelopes of the sigmoid fit. Error bars are computed as discussed in the main text.

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    • Figure 11
      Figure 11

      Wide-band interpolation D95%(f) of the results obtained by the SkyHough pipeline. Each dot represents a D95% at a particular frequency band computed using the procedure exemplified in Fig. 10. The red solid line represents a nonparametric interpolation using a Gaussian process regression, as discussed in the main text. The shaded region represents a 3% relative error with respect to the interpolation and corresponds to the 98% credible interval.

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    • Figure 12
      Figure 12

      CW amplitude h095% corresponding to the 95% detection efficiency depth along the frequency band analyzed by the SkyHough pipeline. Solid line represents the implied h095% from the wide-band D95% interpolation shown in Fig. 11. Shaded region corresponds to the 3% relative error with respect to the interpolation.

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    • Figure 13
      Figure 13

      Comparison of 95% confidence upper limits on GW amplitude h0 obtained with the Time-Domain F-statistic pipeline in the analysis of Advanced LIGO data. The magenta circles, green triangles, and blue squares represent the h095% upper limits in 0.25 Hz sub-bands of the O1, O2, and O3 data, respectively.

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    • Figure 14
      Figure 14

      Detection efficiencies of the SOAP + CNN search on isolated NS signals injected into real O3 data. These are shown as a function of the sensitivity depth for the four different frequency ranges described in Sec. 4d1. The efficiencies are calculated with a false alarm rate of 1%.

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    • Figure 15
      Figure 15

      Comparison of broadband search sensitivities obtained by the FrequencyHough pipeline (black triangles), the SkyHough pipeline (red squares), the Time-Domain F-statistic pipeline (blue circles), and the SOAP pipeline (magenta diamonds). Vertical bars mark errors of h0 obtained in the procedures described in Secs. 4 and 5. Population-averaged upper limits obtained in [39] using the O3a data are marked with dark-green crosses.

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    • Figure 16
      Figure 16

      Left panel: detectable ellipticity, given by Eq. (22), as a function of the GW frequency for neutron stars with the “canonical” moment of inertia Izz=1038  kg m2 at a distance of 10 kpc, 1 kpc, 100 pc, and 10 pc (from top to bottom). Results for the FrequencyHough pipeline are marked in black, SkyHough in red and for Time-Domain F-statistic in blue. The right panel shows the relation between the absolute value of the first GW frequency derivative f˙=2f˙rot and the GW frequency f=2frot (with frot the rotational frequency) of detectable sources as a function of the distance, assuming their spin-down is due solely to the emission of GWs. Constant spin-down ellipticities εsd, corresponding to this condition, are denoted by dashed green curves. The magenta horizontal line marks the maximum spin down searched.

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    • Figure 17
      Figure 17

      Constraints on f˜, a quantity that, if less than one, indicates the sensitivity to a given fpbh, and inspiraling rate (color) as a function of the secondary mass, with a primary mass m1=2.5  M⊙, assuming a monochromatic mass function for m1, no rate suppression, and fpbh=1. These constraints are valid at distances of O(pc).

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