All-sky search for gravitational wave emission from scalar boson clouds around spinning black holes in LIGO O3 data

This paper describes the first all-sky search for long-duration, quasimonochromatic gravitational-wave signals emitted by ultralight scalar boson clouds around spinning black holes using data from the third observing run of Advanced LIGO. We analyze the frequency range from 20 to 610 Hz, over a small frequency derivative range around zero, and use multiple frequency resolutions to be robust towards possible signal frequency wanderings. Outliers from this search are followed up using two different methods, one more suitable for nearly monochromatic signals, and the other more robust towards frequency fluctuations. We do not find any evidence for such signals and set upper limits on the signal strain amplitude, the most stringent being $\approx {10}^{-25}$ at around 130 Hz. We interpret these upper limits as both an “exclusion region” in the boson mass/black hole mass plane and the maximum detectable distance for a given boson mass, based on an assumption of the age of the black hole/boson cloud system.

Figure 1

Scheme of the search pipeline.

Figure 2

Chunk duration $T_{\mathrm{FFT}}$ as a function of frequency. The $T_{\mathrm{FFT}}$ is fixed within each 10-Hz band.

Figure 3

Bin size of the frequency time derivative, $\delta \dot{f}$, a function of the frequency, given the full observing time of O3 and $T_{\mathrm{FFT}}$ chosen for each 10-Hz band. The search by default covers a frequency time derivative range of $\dot{f}\in [-\delta \dot{f}/2,\delta \dot{f}/2]$. Such a range contributes to set constraints on the portion of the boson mass/black hole mass explored in the search.

Figure 4

Time-frequency peakmap (left) and corresponding projection (right) in the frequency band of 28.2–28.35 Hz over the full run. Several instrumental artifacts are visible, e.g. strong lines with varying amplitudes ($\sim 28.22\mathrm{Hz}$), weaker lines with sudden frequency variation ($\sim 28.33\mathrm{Hz}$), and broad transient disturbances (vertical bright lines). In particular, the features around 28.28 Hz in the second half of O3 are responsible for a big bunch of outliers with frequency in the range of 28.279–28.283 Hz.

Figure 5

95% C.L. upper limits on the signal strain amplitude obtained from this search (circles, connected by the dashed line). Values are given in each 1-Hz subband. No value is given for the subbands where no outlier survives. The dots connected by a dashed line define the lower bound obtained using the minimum CR in each subband.

Figure 6

Exclusion regions in the boson mass ($m_b$) and black hole mass ($M_{\mathrm{BH}}$) plane for an assumed distance of $D=1\mathrm{kpc}$ (left) and $D=15\mathrm{kpc}$ (right), and an initial black hole dimensionless spin ${\chi }_i=0.9$. For $D=1\mathrm{kpc}$, three possible values of the black hole age, $t_{\mathrm{age}}={10}^3,{10}^6,{10}^8\mathrm{years}$, are considered; for $D=15\mathrm{kpc}$, $t_{\mathrm{age}}={10}^3,{10}^{4.5},{10}^6\mathrm{years}$ are considered.

Figure 7

Same as Fig. 6 but for black hole initial spin ${\chi }_i=0.5$. The assumed distance is $D=1\mathrm{kpc}$ (left), and $D=15\mathrm{kpc}$ (right).

Figure 8

Maximum distance at which at least 5% of a simulated population of black holes with a boson cloud would produce a gravitational-wave signal with strain amplitude larger than the upper limit in the detectors. The left plot refers to a maximum black hole mass of $50M_{\odot }$, while the right plot to a maximum mass of $100M_{\odot }$. The different colored markers correspond to different system ages, ranging from ${10}^3\mathrm{years}$ to ${10}^7\mathrm{years}$, as indicated in the legend. The alignment of points for different ages at the smallest boson masses (and distances) is the result of a discretization effect due to the finite size grid used in distance.

Figure 9

Critical ratio of the candidates produced by hardware injection P5 in H1 data and found in the search with $W=1$. The distance of the highest CR candidate from the injected signal is about 0.7.

Figure 10

FFT length increase factor, with respect to the main search FFT length, as a function of frequency for FU1. This factor is reduced at the highest frequencies in order to keep the computer memory used by the analysis jobs under control.

Figure 11

FFT length increase factor, with respect to the main search length, as a function of frequency for FU2.

Figure 12

Critical ratio of the main search H1 (left) and L1 (right) outliers with $W=1$.

Figure 13

Critical ratio of the main search H1 (left) and L1 (right) outliers with $W>1$.

Figure 14

Critical ratios of outliers passing FU1 follow-up stage as a function of their frequencies (circles: Livingston, stars: Hanford).

Figure 15

Time-frequency peakmap of H1 data after FU1 follow-up stage showing a distinct broad disturbance appearing in the second half of the run and responsible for the 22 outliers identified with frequency $\sim 69.55\mathrm{Hz}$. Time is measured in days since the stsrting of the run. The colorbar represents a power spectrum in units of ${10}^{-40}$ [$1/\mathrm{Hz}$].

Figure 16

Time-frequency peakmap of H1 data after FU2 around the outlier with frequency $\sim 61.44\mathrm{Hz}$. Time is measured in days since the starting of the run. A transient disturbance, starting from $\sim 20$ days before the end of the run, is clearly visible. The color bar represents power spectrum in units of ${10}^{-40}$ [$1/\mathrm{Hz}$].