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General Relativity and Quantum Cosmology, gr-qc
Abstract:
The sensitivity of gravitational wave searches for binary black holes is
estimated via the injection and posterior recovery of simulated gravitational
wave signals in the detector data streams. When a search reports no detections,
the estimated sensitivity is then used to place upper limits on the coalescence
rate of the target source. In order to obtain correct sensitivity and rate
estimates, the injected waveforms must be faithful representations of the real
signals. Up to date, however, injected waveforms have neglected radiation modes
of order higher than the quadrupole, potentially biasing sensitivity and
coalescence rate estimates. In particular, higher-order modes are known to have
a large impact in the gravitational waves emitted by intermediate mass black
holes binaries. In this work we evaluate the impact of this approximation in
the context of two search algorithms run by the LIGO Scientific Collaboration
in their search for intermediate mass black hole binaries in the O1 LIGO
Science Run data: a matched-filter based pipeline and a coherent un-modeled
one. To this end we estimate the sensitivity of both searches to simulated
signals including and omitting higher-order modes. We find that omission of
higher-order modes leads to biases in the sensitivity estimates which depend on
the masses of the binary, the search algorithm and the required level of
significance for detection. In addition, we compare the sensitivity of the two
search algorithms across the studied parameter space. We conclude that the most
recent LIGO-Virgo upper limits on the rate of coalescence of intermediate mass
black hole binaries are conservative for the case of highly asymmetric
binaries. However, the tightest upper limits, placed for nearly-equal-mass
sources, remain unchanged due to the small contribution of higher modes to the
corresponding sources.
