Abstract
We analyse the effects of microlensing in the LIGO/Virgo frequency band due
to a population of stellar-mass microlenses and study their implications for
strongly lensed gravitational wave (GW) signals. We consider a wide range of
strong lensing magnifications and the corresponding surface densities of the
microlens population found in lensing galaxies, and use them to generate
realisations of the amplification factor. The methodologies for simulating
amplification curves for both type-I (minima) and type-II (saddle) images are
also discussed. We find that, on average, the presence of microlens population
introduces a net amplification (de$-$amplification) in minima (saddle points)
type of images in the LIGO frequency range. With increasing microlens density,
the overall scatter and distortions increase and become significant from
relatively lower frequencies. Comparison between IMFs suggests that although
the differences are not significant in typical cases, the bottom-heavy IMF
tends to show a steeper rise in the scatter due to microlensing at higher
frequencies compared to a bottom-light IMF. However, with the increase in the
strong lensing magnification, the effects of microlensing become increasingly
significant regardless of other parameters, such as the microlens density, type
of images or the IMF of the population. Hence, for microlensing features to be
notable in GW signal, the strong lensing magnification needs to be substantial.
In some extreme cases of strong lensing magnification ($\sim100$), the mismatch
between lensed and unlensed waveforms of compact binary coalescences can reach
as high as $\sim6\%$. While for most of the typical microlens densities and
strong lensing magnifications the mismatch remains less than $1\%$ (showing
that the waveforms will not miss detection by LIGO/Virgo, in general),
nevertheless their inferred source parameters may still be affected.
Description
Gravitational Lensing of Gravitational Waves: Effect of Microlens Population in Lensing Galaxies
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