This work studies microlensing effects in strongly lensed gravitational wave (GW) signals corresponding to global minima images in galaxy-scale lenses. We find that stellar microlenses alone are unable to introduce noticeable wave effects in the global minima GW signals at strong lensing magnification $( {\mu})\lt 50$ with match value between unlensed and lensed GW signals being above ${\sim }99.5~{{\ \rm per \, cent}}$ in ${\sim }90~{{\ \rm per \, cent}}$ of systems implying that GW signals corresponding to global minima can be treated as reference signal to determine the amount of microlensing in other strongly lensed counterparts. Since the stellar microlenses introduce negligible wave effects in global minima, they can be used to probe the intermediate-mass black hole (IMBH) lenses in the galaxy lens. We show that the presence of an IMBH lens with mass in the range $[50,10^3]~{\rm M_\odot }$ such that the global minima lies within five Einstein radius of it, the microlensing effects at $f\lt 10^2$ Hz are mainly determined by the IMBH lens for ${\mu} \lt 50$. Assuming that a typical strong lensing magnification of 3.8 and high enough signal-to-noise ratio (in the range ${\simeq }[10, 30]$) to detect the microlensing effect in GW signals corresponding to global minima, with non-detection of IMBH-led microlensing effects in ${\simeq }15~({\simeq }150)$ lensed GW signals, we can rule out dark matter fraction $\gt 10~{{\ \rm per \, cent}}~(\gt 1~{{\ \rm per \, cent}})$ made of IMBH population inside galaxy lenses with mass values $\gt 150~{\rm M_\odot }$ with ${\sim }$90 per cent confidence. Although we have specifically used IMBHs as an example, the same analysis applies to any subhalo (or compact objects) with lensing masses (i.e. the total mass inside Einstein radius) satisfying the above criterion.
Gravitational lensing is the phenomenon where the presence of matter (called a lens) bends the path of light-like trajectories travelling nearby. Similar to the geometric optics limit of electromagnetic waves, gravitational lensing of gravitational waves (GWs) can occur in geometric optics condition when GW wavelength is much smaller than the Schwarzschild radius of the lens, that is, $\lambda _{\mathrm{ GW}} \ll$R$^{\rm s}_{\rm lens}$. This is known as the strong lensing regime for which a multiple-image system with different magnifications and phase shifts is formed. We developed GLANCE, Gravitational Lensing Authenticator using Non-modelled Cross-correlation Exploration, a novel technique to detect strongly lensed GW signals. We demonstrate that cross-correlation between two noisy reconstruction of polarized GW signals shows a non-zero value when the signals are lensed counterparts. The relative strength between the signal cross-correlation and noise cross-correlation can quantify the significance of the event(s) being lensed. Since lensing biases the inference of source parameters, primarily the luminosity distance, a joint parameter estimation of the source and lens-induced parameters is incorporated using a Bayesian framework. We applied GLANCE to synthetic strong lensing data and showed that it can detect lensed GW signals and correctly constrain the injected source and lens parameters, even when one of the signals is below match-filtered threshold signal-to-noise ratio. This demonstrates GLANCE’s capability as a robust detection technique for strongly lensed GW signals and can distinguish between lensed and unlensed events.
more » « less- PAR ID:
- 10531580
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Monthly Notices of the Royal Astronomical Society
- Volume:
- 532
- Issue:
- 4
- ISSN:
- 0035-8711
- Format(s):
- Medium: X Size: p. 4842-4863
- Size(s):
- p. 4842-4863
- Sponsoring Org:
- National Science Foundation
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