Observational signatures of microlensing in gravitational waves at LIGO/Virgo frequencies

Abstract

Microlenses with typical stellar masses (a few M ) have traditionally been disregarded as potential sources of gravitational lensing effects at LIGO/Virgo frequencies, since the time delays are often much smaller than the inverse of the frequencies probed by LIGO/Virgo, resulting in negligible interference effects at LIGO/Virgo frequencies. While this is true for isolated microlenses in this mass regime, we show how, under certain circumstances and for realistic scenarios, a population of microlenses (for instance stars and remnants from a galaxy halo or from the intracluster medium) embedded in a macromodel potential (galaxy or cluster) can conspire together to produce time delays of order one millisecond which would produce significant interference distortions in the observed strains. At sufficiently large magnification factors (of several hundred), microlensing effects should be common in gravitationally lensed gravitational waves. We explore the regime where the predicted signal falls in the frequency range probed by LIGO/Virgo. We find that stellar mass microlenses, permeating the lens plane, and near critical curves, can introduce interference distortions in strongly lensed gravitational waves. For those lensed events with negative parity, (or saddle points, never studied before in the context of gravitational waves), and that take place near caustics of macromodels, they are more likely to produce measurable interference effects at LIGO/Virgo frequencies. This is the first study that explores the effect of a realistic population of microlenses, plus a macromodel, on strongly lensed gravitational waves.

Gravitational wave interference via gravitational lensing: Measurements of luminosity distance, lens mass, and cosmological parameters

“…By Ref. [16], the effect of the microlensing is prominent when the magnification of the strong lensing is about a few hundreds to a few thousands, that is, when the saturation regime is reached. In the following scenarios to be discussed, the saturation is never reached, so the microlensing effect is negligible.…”

Localizing merging black holes with sub-arcsecond precision using gravitational-wave lensing

“…We've neglected the line of sight contribution to the H0 error, but this could be included in future work. We note that microlensing can be suppressed for GWs due to diffraction effects in the case of stellar-mass microlenses (Oguri 2019) (except in the case of extreme macromodel magnification (Diego, J. M. et al 2019)). A dedicated study towards gravitational-wave microlensing will be needed to quantify a more realistic estimate of the magnification uncertainties due to microlensing.…”

“…The dashed line shows the simulated value of H 0 = 70 kms −1 Mpc −1 . mass BBH gravitational wave emission (Oguri 2019) (except in the case of extreme macro model magnification (Diego, J. M. et al 2019)). A dedicated study towards gravitational-wave microlensing will be needed to quantify a more realistic estimate of the magnification uncertainties due to microlensing.…”

“…GW contains higher-order modes and passes through a lensing saddle point, the signal morphology could exhibit a minor change. Moreover, if beating patterns induced by microlensing are present, there could be minor changes to the waveform in the case of extreme macromodel magnification Diego, J. M. et al (2019); Pagano et al (2020). However, the effects are rare, and are not expected to significantly affect parameter estimation.…”

The Legacy of Einstein’s Eclipse, Gravitational Lensing

“…On the other hand, extra features as time delays and consequently interference distortions in signal can be introduced by microlensing [188] and by wave optics effects if GW are observed with sufficiently high signal-to-noise ratios.…”