Nishkal Rao | Searcharxiv

arXiv2026

Highly eccentric non-spinning binary black hole mergers: quadrupolar post-merger waveforms

We present numerically-informed closed-form expressions for the dominant $(\ell,m)=(2,2)$ waveform harmonic of the post-merger emission from mergers of non-spinning binary black holes with comparable masses on highly eccentric orbits. Using 233 non-spinning eccentric simulations from the RIT catalog, we construct time-dependent complex quasinormal mode amplitudes via a Bayesian procedure. We build multivariate polynomial models, represented as functions of the symmetric mass ratio $ν$ and two dynamics parameters evaluated at merger: the mass-rescaled effective energy $\hat{E}_{\mathrm{eff}}^{\mathrm{mrg}}$ and angular momentum $j_{\mathrm{mrg}}$. We further validate the post-merger non-circular waveform model by comparing it against simulations from the SXS catalog. Our models achieve mismatches around $\sim10^{-3}$, including for near-extreme eccentricities. The model can be directly combined with effective-one-body and phenomenological inspiral waveforms to produce accurate inspiral-merger-ringdown waveforms, essential for parameter estimation of both astrophysical and fundamental physics properties of the signals' sources.

gr-qc↗

arXiv2026

Comprehensive analysis of time-domain overlapping gravitational wave transients: A Lensing Study

Next-generation GW detectors will produce a high rate of temporally overlapping signals from unrelated compact binary coalescences. Such overlaps can bias parameter estimation (PE) and mimic signatures of other physical effects, such as gravitational lensing. In this work, we investigate how overlapping signals can be degenerate with gravitational lensing by focusing on two scenarios: Type-II strong lensing and microlensing by an isolated point-mass lens. We simulate quasicircular binary black-hole pairs with chirp-mass ratios $\mathscr{M}_{\rm B}/\mathscr{M}_{\rm A}\in\{0.5,\,1,\,2\}$, SNR ratios $\mathrm{SNR}_{\rm B}/\mathrm{SNR}_{\rm A}\in\{0.5,\,1\}$, and coalescence-time offsets $Δt_{\rm c}\in[-0.1,\,0.1]~\mathrm{s}$. Bayesian PE and fitting-factor studies show that the Type-II lensing hypothesis is favored over the unlensed quasicircular hypothesis ($\log_{10}\mathscr{B}^{\rm L}_{\rm U}>1$) only in a small region of the overlapping parameter space with $\mathscr{M}_{\rm B}/\mathscr{M}_{\rm A}\gtrsim1$ and $|Δt_{\rm c}|\leq0.03~\rm{s}$.. Meanwhile, false evidence for microlensing signatures can arise because, to a reasonable approximation, the model produces two superimposed images whose time delay can closely match $|Δt_{\rm c}|$. Overall, the inferred Bayes factor depends on relative chirp-mass ratios, relative loudness, difference in coalescence times, and also the absolute SNRs of the overlapping signals. Cumulatively, our results indicate that overlapping black-hole binaries with nearly equal chirp masses and comparable loudness are likely to be falsely identified as lensed. Such misidentifications are expected to become more common as detector sensitivities improve. While our study focuses on ground-based detectors using appropriate detectability thresholds, the findings naturally extend to next-generation GW observatories.

gr-qc↗