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Impact of gravitational radiation higher order modes on single aligned-spin gravitational wave searches for binary black holes

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 Publication date 2015
  fields Physics
and research's language is English




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Current template-based gravitational wave searches for compact binary coalescences (CBC) use waveform models that neglect the higher order modes content of the gravitational radiation emitted, considering only the quadrupolar $(ell,|m|)=(2,2)$ modes. We study the effect of such a neglection for the case of aligned-spin CBC searches for equal-spin (and non-spinning) binary black holes in the context of t



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The possible formation of stellar-mass binary black holes through dynamical interactions in dense stellar environments predicts the existence of binaries with non-negligible eccentricity in the frequency band of ground-based gravitational wave detectors; the detection of binary black hole mergers with measurable orbital eccentricity would validate the existence of this formation channel. Waveform templates currently used in the matched-filter gravitational-wave searches of LIGO-Virgo data neglect effects of eccentricity which is expected to reduce their efficiency to detect eccentric binary black holes. Meanwhile, the sensitivity of coherent unmodeled gravitational-wave searches (with minimal assumptions about the signal model) have been shown to be largely unaffected by the presence of even sizable orbital eccentricity. In this paper, we compare the performance of two state-of-the-art search algorithms recently used by LIGO and Virgo to search for binary black holes in the second Observing Run (O2), quantifying their search sensitivity by injecting numerical-relativity simulations of inspiral-merger-ringdown eccentric waveforms into O2 LIGO data. Our results show that the matched-filter search PyCBC performs better than the unmodeled search cWB for the high chirp mass ($>20 M_{odot}$) and low eccentricity region ($e_{30 Hz} < 0.3$) of parameter space. For moderate eccentricities and low chirp mass, on the other hand, the unmodeled search is more sensitive than the modeled search.
Gravitational wave templates used in current searches for binary black holes omit the effects of precession of the orbital plane and higher order modes. While this omission seems not to impact the detection of sources having mass ratios and spins similar to those of GW150914, even for total masses $M > 200M_{odot}$; we show that it can cause large fractional losses of sensitive volume for binaries with mass ratio $q geq 4$ and $M>100M_{odot}$, measured the detector frame. For the highest precessing cases, this is true even when the source is face-on to the detector. Quantitatively, we show that the aforementioned omission can lead to fractional losses of sensitive volume of $sim15%$, reaching $>25%$ for the worst cases studied. Loss estimates are obtained by evaluating the effectualness of the SEOBNRv2-ROM double spin model, currently used in binary black hole searches, towards gravitational wave signals from precessing binaries computed by means of numerical relativity. We conclude that, for sources with $q geq 4$, a reliable search for binary black holes heavier than $M>100M_odot$ needs to consider the effects of higher order modes and precession. The latter seems specially necessary when Advanced LIGO reaches its design sensitivity.
Estimates of the source parameters of gravitational-wave (GW) events produced by compact binary mergers rely on theoretical models for the GW signal. We present the first frequency-domain model for inspiral, merger and ringdown of the GW signal from precessing binary-black-hole systems that also includes multipoles beyond the leading-order quadrupole. Our model, {tt PhenomPv3HM}, is a combination of the higher-multipole non-precessing model {tt PhenomHM} and the spin-precessing model {tt PhenomPv3} that includes two-spin precession via a dynamical rotation of the GW multipoles. We validate the new model by comparing to a large set of precessing numerical-relativity simulations and find excellent agreement across the majority of the parameter space they cover. For mass ratios $<5$ the mismatch improves, on average, from $sim6%$ to $sim 2%$ compared to {tt PhenomPv3} when we include higher multipoles in the model. However, we find mismatches $sim8%$ for the mass-ratio $6$ and highly spinning simulation. As a first application of the new model we have analysed the binary black hole event GW170729. We find larger values for the primary black hole mass of $58.25^{+11.73}_{-12.53} , M_odot$ (90% credible interval). The lower limit ($sim 46 , M_odot$) is comparable to the proposed maximum black hole mass predicted by different stellar evolution models due to the pulsation pair-instability supernova (PPISN) mechanism. If we assume that the primary ac{BH} in GW170729 formed through a PPISN then out of the four PPISN models we considered only the model of Woosley (2017) is consistent with our mass measurements at the 90% level.
We investigate the observability of higher harmonics in gravitational wave signals emitted during the coalescence of binary black holes. We decompose each mode into an overall amplitude, dependent upon the masses and spins of the system, and an orientation-dependent term, dependent upon the inclination and polarization of the source. Using this decomposition, we investigate the significance of higher modes over the parameter space and show that the $ell = 3$, $m = 3$ mode is most significant across much of the sensitive band of ground-based interferometric detectors, with the $ell = 4$, $m = 4$ having a significant contribution at high masses. We introduce the higher mode signal-to-noise ratio (SNR), and show that a simple threshold on this SNR can be used as a criterion for observation of higher harmonics. Finally, we investigate observability in a population of binaries and observe that higher harmonics will only be observable in a few percent of binaries, typically those with unequal masses and viewed close to edge-on.
A waveform model for the eccentric binary black holes named SEOBNRE has been used to analyze the LIGO-Virgos gravitational wave data by several groups. The accuracy of this model has been validated by comparing it with numerical relativity. However, SEOBNRE is a time-domain model, and the efficiency for generating waveforms is a bottleneck in data analysis. To overcome this disadvantage, we offer a reduced-order surrogate model for eccentric binary black holes based on the SEOBNRE waveforms. This surrogate model (SEOBNRE_S) can simulate the complete inspiral-merger-ringdown waves with enough accuracy, covering eccentricities from 0 to 0.25 (0.1), and mass ratio from 1:1 to 5:1 (2:1) for nonspinning (spinning) binaries. The speed of waveform generation is accelerated about $10^2 sim 10^3$ times than the original SEOBNRE model. Therefore SEOBNRE_S could be helpful in the analysis of LIGO data to find potential eccentricities.
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