arXiv subjects

Yumeng Xu

Publications and source records attributed to Yumeng Xu.

10 recordsLinked to original sources

arXiv2026

A stepping stone toward detecting gravitational wave memory: a cumulative analysis with the full $(\ell=2, m=0)$ spherical harmonic using events from GWTC-4.0 and GWTC-5.0

We perform Bayesian model selection to test for the presence of the $(\ell=2,m=0)$ spherical harmonic mode in gravitational wave events that have previously been identified as binary black hole mergers. As our signal model we use the quasi-circular, non-precessing IMRPhenomTHM_20 waveform model, which includes the oscillatory and displacement memory contributions. Including the oscillatory component of the (2,0) mode increases the signal-to-noise ratio and evidence for this mode, compared to testing only for the presence of gravitational wave memory. Our analysis thus constitutes a natural stepping stone toward detecting gravitational wave memory. We perform our analysis for the binary black hole signals identified in the GWTC-4.0 catalog, and for selected GWTC-5.0 events. In our Bayesian model comparison we find a cumulative $\log_{10}\mathcal{B}=1.38\pm0.79$ in favor of the presence of the (2,0) mode for the GWTC-4.0 catalog. We also stack the signal-to-noise ratio of the full (2,0) mode and of its individual contributions, obtaining results consistent with previous studies and reaching $\mathrm{SNR}_{\mathrm{memory}} = 0.89^{+0.29}_{-0.11}$ after approximately 7.5 months of O4a observations. In addition, we study the precessing candidate GW241127_061008, and find no additional evidence for the (2,0) mode when precession is included in IMRPhenomTPHM_20. Overall, our results provide an assessment of the observational support for the (2,0) mode in current gravitational wave data and allow us to discuss prospects for its future detection. We find that decisive statistical evidence will likely require a larger catalog, with an optimistic estimated number of events of $N_{\mathrm{events}} = 166^{+82}_{-55}$, based on the specific assumptions adopted in this work. We also expect that decisive evidence will require a more extensive waveform systematics study.

gr-qc↗

arXiv2026

Remnant recoil and host environments of GWTC-4.0 binary black-hole mergers

Determining the astrophysical origin of binary black holes and whether merger remnants are retained in their birth environments is essential for understanding hierarchical mergers and the growth of intermediate-mass black holes. We identified gravitational-wave events most consistent with dense-cluster origin and assessed whether their merger remnants are retained in globular clusters, nuclear star clusters, or galactic potentials. We considered 84 events consistent with binary-black-hole mergers from the first part of the fourth observing run (O4a) of the LIGO-Virgo-KAGRA detector network, and 3 selected events from the second part (O4b). We compared parameter-estimation posteriors with synthetic population models for field and cluster binaries using Bayes factors, accounting for the relative abundances of these formation channels. We computed recoil-velocity posteriors for all events using the IMRPhenomXPNR waveform model. We identified five events whose intrinsic parameters show preference for the adopted dense-cluster models over the considered field-binary populations, including the most massive O4a event GW231123_135430, while finding no robust preference for a dense-cluster origin for the high-spinning O4b event GW241011_233834. Typical recoil velocities are a few hundred km/s, with extended high-velocity tails. These kicks suggest merger remnants are likely ejected from typical globular clusters, while retention in nuclear star clusters remains possible but not guaranteed. Within the adopted models, efficient hierarchical growth may be challenging in typical globular clusters, whereas nuclear star clusters remain viable environments for repeated mergers. Although results depend on the adopted population models, this analysis highlights the importance of improved population models and higher-quality detections enabled by future GW detectors.

astro-ph.HE↗

arXiv2025

Parameter estimation for the GWTC-4.0 catalog with phenomenological waveform models that include orbital eccentricity and an updated description of spin precession

The GWTC-4.0 catalog of transient gravitational wave signals describes observations made in the first part of the fourth observing run of the LIGO-Virgo-KAGRA (LVK) gravitational wave detector network. Here we extend the LVK's GWTC-4.0 analysis to elliptic orbits, and an improved description of spin precession in the frequency domain. For this study we use state-of-the-art waveforms from the IMRPhenom family (specifically XPNR, TPHM, and TEHM), and we consider the 84 confidently detected events that are consistent with binary-black-hole mergers. We present an extended catalog of updated posterior samples, quantify how incorporation of these waveform effects alters inferred source properties relative to previous analyses, and discuss waveform systematics.

gr-qc↗

arXiv2025

Optimizing searches for gravitational wave bursts using coherent WaveBurst 2G

The most general searches for gravitational wave transients (GWTs) rely on data analysis methods that do not assume prior knowledge of the signal waveform, direction, or arrival time on Earth. These searches provide data-driven signal reconstructions that are crucial both for testing available emission models and for discovering yet-to-be-uncovered sources. Here, we discuss progress in the detection performance of the coherent WaveBurst second-generation pipeline (cWB-2G), which is highly adaptable to both minimally modeled and model-informed searches for GWTs. Several search configurations for GWTs are examined using approximately 14.8 days of observation time from the third observing run by LIGO-Virgo-KAGRA (LVK). Recent enhancements include a ranking statistic fully based on multivariate classification with eXtreme Gradient Boosting, a thorough validation of the statistical significance accuracy of GWT candidates, and a measurement of the correlations of false alarms and simulated detections between different concurrent searches. For the first time, we provide a comprehensive comparison of cWB-2G performance on data from networks made of two and three detectors, and we demonstrate the advantage of combining concurrent searches for GWTs of generic morphology in a global observatory. This work offers essential insights for assessing our data analysis strategies in ongoing and future LVK searches for generic GWTs.

gr-qc↗

arXiv2025

Detectability of massive binary black holes with sub-mHz gravitational wave missions

Beyond LISA, proposed space-based gravitational wave (GW) missions aim to explore the sub-millihertz to microhertz frequency band, with one key objective being the detection of massive binary black hole (MBBH) mergers across cosmic distances. In this work, we investigate the detection and localization capabilities of future sub-mHz GW observatories for MBBH coalescences. Including the full galactic foreground noise, we find that signal-to-noise ratios (SNRs) can reach several thousand across a wide range of redshifts. We evaluate three representative orbital configurations--non-precessing and precessing with different inclination angles--and analyze their localization performance for various MBBH populations. In the non-precessing case, a two-hemisphere degeneracy arises when only the dominant (2,2) mode is considered, which is effectively resolved by including higher-order modes. These modes contribute to a more uniform performance across all configurations, thereby mitigating the prior advantage of precessing mission orbits. Sub-mHz missions operating in the [10 $μ$Hz, 10 mHz] band partially overlap with LISA's range but provide enhanced sensitivity to lower-frequency GWs due to their longer interferometric baselines. This results in significantly improved localization of high-mass MBBHs, enhancing the prospects for multi-messenger astronomy and precision cosmology. Moreover, the high SNRs attainable with sub-mHz detectors could enable stringent tests of general relativity and alternative theories of gravity.

gr-qc↗

arXiv2025

Impact of the $(\ell=2,m=0)$ spherical harmonic mode with memory on parameter estimation for ground-based detectors

We recently presented an efficient and accurate waveform model for the $(2,0)$ spherical harmonic mode including both the displacement memory contribution and the ringdown oscillations for aligned-spin binary black holes in quasi-circular orbits. The model we developed is constructed in time domain and implemented within the computationally efficient IMRPhenomTHM waveform model. In this article, we employ it to perform in-depth parameter estimation studies for future ground-based detectors, specifically considering LIGO A$^{\#}$, Cosmic Explorer, and the Einstein Telescope, combining them in different detector networks. While previous studies have reviewed the impact of the memory contribution in parameter estimation, we assess the effect of incorporating the complete mode in the analysis on the posterior estimation of source parameters, performing zero-noise injections of high signal-to-noise ratio signals. We investigate the impact of this mode on the distance-inclination degeneracy and compare its impact in edge-on and face-on configurations. We find that including this mode helps mitigate biases in the estimation of individual spin components, which may otherwise arise when the mode is neglected.

gr-qc↗

arXiv2024

Enhancing Gravitational Wave Parameter Estimation with Non-Linear Memory: Breaking the Distance-Inclination Degeneracy

In this study, we investigate the role of the non-linear memory effect in gravitational wave (GW) parameter estimation, particularly we explore its capability to break the degeneracy between luminosity distance and inclination angle in binary coalescence events. Motivated by the rapid growth in GW detections and the increasing sensitivity of GW observatories enhancing the precision of cosmological and astrophysical measurements is crucial. We propose leveraging the non-linear memory effect -- a subtle, persistent feature in the GW signal resulting from the cumulative impact of emitted gravitational waves -- as a novel approach to enhance parameter estimation accuracy. Through a comprehensive series of injection studies, encompassing both reduced and full parameter spaces, we evaluate the effectiveness of non-linear memory in various scenarios for aligned-spin systems. Our findings demonstrate the significant potential of non-linear memory in resolving the inclination-distance degeneracy, particularly for events with high signal-to-noise ratios (SNR $>$ 90) for the current generation of detectors or closer than 1 Gpc in the context of future detector sensitivities such as the planned LIGO A$^\sharp$ upgrade. The results also suggest that excluding non-linear memory from parameter estimation could introduce significant systematics in future LIGO A$^\sharp$ detections. This observation will hold even greater weight for next-generation detectors, highlighting the importance of including non-linear memory in GW models for achieving high-accuracy measurements for gravitational wave (GW) astronomy.

gr-qc↗

arXiv2024

Search for hyperbolic encounters of compact objects in the third LIGO-Virgo-KAGRA observing run

Gravitational-wave (GW) observations provide unique information about compact objects. As detectors sensitivity increases, new astrophysical sources of GW could emerge. Close hyperbolic encounters are one such source class: scattering of stellar mass compact objects is expected to manifest as GW burst signals in the frequency band of current detectors. We present the search for GW from hyperbolic encounters in the second half of the third Advanced LIGO-Virgo observing run (O3b). We perform a model-informed search with machine-learning enhanced Coherent WaveBurst algorithm. No significant event has been identified in addition to known detections of compact binary coalescences. We inject in the O3b data non-spinning third Post-Newtonian order accurate hyperbolic encounter model with component masses between [2, 100] $M_{\odot}$, impact parameter in [60, 100] ${GM}/{c^2}$ and eccentricity in [1.05, 1.6]. We further discuss the properties of the simulation recovered. For the first time, we report the sensitivity volume achieved for such sources, which for O3b data reaches up to 3.9$\pm 1.4 \times 10^5$ Mpc$^3$year for compact objects with masses between [20, 40] $M_{\odot}$, corresponding to a rate density upper limit of 0.589$\pm$0.094 $\times10^{-5}$Mpc$^{-3}$year$^{-1}$. Finally, we present projected sensitive volume for the next observing runs of current detectors, namely O4 and O5.

gr-qc↗

arXiv2023

PycWB: A User-friendly, Modular, and Python-based Framework for Gravitational Wave Unmodelled Search

Unmodelled searches and reconstruction is a critical aspect of gravitational wave data analysis, requiring sophisticated software tools for robust data analysis. This paper introduces PycWB, a user-friendly and modular Python-based framework developed to enhance such analyses based on the widely used unmodelled search and reconstruction algorithm Coherent Wave Burst (cWB). The main features include a transition from C++ scripts to YAML format for user-defined parameters, improved modularity, and a shift from complex class-encapsulated algorithms to compartmentalized modules. The pycWB architecture facilitates efficient dependency management, better error-checking, and the use of parallel computation for performance enhancement. Moreover, the use of Python harnesses its rich library of packages, facilitating post-production analysis and visualization. The PycWB framework is designed to improve the user experience and accelerate the development of unmodelled gravitational wave analysis.

gr-qc↗

arXiv2023

Measurability of precession and eccentricity for heavy binary-black-hole mergers

Gravitational wave detections offer insights into the astrophysical populations of black holes in the universe and their formation processes. Detections of binaries consisting of black holes lying outside the bulk distribution of the astrophysical population are particularly intriguing. In this study, we perform an injection analysis within the intermediate-mass black hole range, utilizing the NR surrogate model NRSur7dq4 and a selection of NR waveforms from the SXS and RIT catalogues. Our investigation focuses on the detectability of precession and its potential degeneracy with eccentricity, especially for short signals with only a few cycles in band. While total mass, mass ratio, and $χ_\mathrm{eff}$ are generally well recovered, the recovery of $χ_\mathrm{p}$ is largely limited, and noise significantly impacts the recovery of some parameters for short signals. We also find that eccentricity lower than 0.2 is insufficient to mimic precession in parameter estimation when assuming a quasi-circular signal. Our results suggest that a certain degree of precession is necessary to produce evidence of high precession in parameter estimation, but it remains challenging to conclusively determine which effect is responsible for the high precession observed in events like GW190521. We emphasize the importance of caution when interpreting properties of a binary from short signals and highlight the potential benefits of future third generation detectors and eccentric waveform models for more exhaustive exploration of parameter space.

gr-qc↗