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General Relativity and Quantum Cosmology, gr-qc,Astrophysics, Cosmology and Extragalactic Astrophysics, astro-ph.CO
Abstract:
When gravitational waves pass near a gravitating object, they are deflected,
or lensed. If the object is massive, such that the wavelength of the waves is
small compared to its gravitational size, lensed gravitational wave events can
be identified when multiple signals are detected at different times. However,
when the wavelength is long, wave-optics diffraction effects will be important,
and a lensed event can be identified by looking for frequency-dependent
modulations to the gravitational waveform, without having to associate multiple
signals. For current ground-based gravitational wave detectors observing
stellar-mass binary compact object mergers, wave-optics effects are important
for lenses with masses $\lesssim 1000 M_{\odot}$. Therefore, minihalos below
this mass range could potentially be identified by lensing diffraction. The
challenge with analyzing these events is that the frequency-dependent lensing
modulation, or the amplification factor, is prohibitively expensive to compute
for Bayesian parameter inference. In this work, we use a novel time-domain
method to construct interpolators of the amplification factor for the
Navarro-Frenk-White (NFW), generalized singular isothermal sphere (gSIS) and
cored isothermal sphere (CIS) lens models. Using these interpolators, we
perform Bayesian inference on gravitational-wave signals lensed by minihalos
injected in mock detector noise, assuming current sensitivity of ground-based
detectors. We find that we could potentially identify an event when it is
lensed by minihalos and extract the values of all lens parameters in addition
to the parameters of the GW source. All of the methods are implemented in
Glworia, the accompanying open-source Python package, and can be generalized to
study lensed signals detected by current and next-generation detectors.
