arXiv subjects

Quynh Lan Nguyen

Publications and source records attributed to Quynh Lan Nguyen.

6 recordsLinked to original sources

arXiv2026

Search for continuous gravitational waves from neutron stars in five globular clusters in the first part of the fourth LIGO-Virgo-KAGRA observing run

We present the results of directed searches for continuous gravitational waves from unknown neutron stars in five Milky Way globular clusters. We carry out these searches in the LIGO data from the first eight months of the fourth LIGO-Virgo-KAGRA observing run using the WEAVE semicoherent program, which sums matched-filter detection-statistic values over many time segments spanning the observation period. No gravitational wave signal is detected in the search band of 20-475 Hz. Injections of simulated continuous wave signals in the data indicate that we achieve the most sensitive results to date across most of the explored parameter space volume, obtaining median 95% confidence level upper limits as low as $\sim 4.2 \times 10^{-26}$ near 282 Hz for NGC 6397. We also derive upper limits on neutron star ellipticity and $r$-mode amplitudes, reaching $\lesssim 10^{-5}$ and $\lesssim 10^{-3}$, respectively, at frequencies above 200 Hz.

gr-qc↗

arXiv2025

Weak Lensing Approximation of Wave-optics Effects from General Symmetric Lens Profiles

Gravitational lensing of electromagnetic (EM) waves has yielded many profound discoveries across fundamental physics, astronomy, astrophysics, and cosmology. Similar to EM waves, gravitational waves (GWs) can also be lensed. When their wavelength is comparable to the characteristic scale of the lens, wave-optics (WO) effects manifest as frequency-dependent modulations in the GW waveform. These WO features encode valuable information about the lensing system but are challenging to model, especially in the weak lensing regime, which has a larger optical depth than strong lensing. We present a novel and efficient framework to accurately approximate WO effects induced by general symmetric lens profiles. Our method is validated against numerical calculations and recovers the expected asymptotic behavior in both high- and low-frequency limits. Accurate and efficient modeling of WO effects in the weak lensing regime will enable improved lens reconstruction, delensing of standard sirens, and provide a unique probe to the properties of low-mass halos with minimal baryonic content, offering new insights into the nature of dark matter.

gr-qc↗

arXiv2025

Algorithm for Dark Matter-Admixed Neutron Stars

Gravitational-wave observations provide a unique window into the fundamental nature of massive objects. In particular, neutron star equations of state have been constrained due to the success of gravitational wave observatories. Recently, the possibility of detecting dark matter-admixed Neutron stars via ground-based laser interferometry have been explored. Dark matter would impact the gravitational waveform of an inspiraling neutron star system through tidal parameters, namely the tidal deformability $λ$, incurring a phase shift to the frequency evolution of the signal. This phase shift would depend both on the percentage of dark matter within the star and its particle nature, e.g., bosonic or fermionic. Indirect detection of dark matter through admixture within neutron stars can provide insight into the neutron equation of state, as well as constraints on the density of dark matter in the universe. In this work, we introduce Darksuite, a proposed extension of the LALSuite software framework, designed to model the gravitational wave signatures of dark-matter-admixed neutron stars. This framework employs simulations from the two-fluid, generally relativistic Tolman- Oppenheimer-Volkoff equations, wherein one fluid is ordinary nuclear matter and the other is dark matter. We demonstrate interpolation of values from a bank of simulations, enabling the study of binary systems where at least one component may be a dark-matter-admixed neutron star. By leveraging existing methodologies within LALSuite for tidal phase corrections and supplementing them with dark matter effects, Darksuite provides a means to generate and analyze gravitational waveforms for these exotic systems.

astro-ph.HE↗

arXiv2025

Multi-messenger Gravitational Lensing

We introduce the rapidly emerging field of multi-messenger gravitational lensing - the discovery and science of gravitationally lensed phenomena in the distant universe through the combination of multiple messengers. This is framed by gravitational lensing phenomenology that has grown since the first discoveries in the 20th century, messengers that span 30 orders of magnitude in energy from high energy neutrinos to gravitational waves, and powerful "survey facilities" that are capable of continually scanning the sky for transient and variable sources. Within this context, the main focus is on discoveries and science that are feasible in the next 5-10 years with current and imminent technology including the LIGO-Virgo-KAGRA network of gravitational wave detectors, the Vera C. Rubin Observatory, and contemporaneous gamma/X-ray satellites and radio surveys. The scientific impact of even one multi-messenger gravitational lensing discovery will be transformational and reach across fundamental physics, cosmology and astrophysics. We describe these scientific opportunities and the key challenges along the path to achieving them. This article is the introduction to the Theme Issue of the Philosophical Transactions of The Royal Society A on the topic of Multi-messenger Gravitational Lensing, and describes the consensus that emerged at the associated Theo Murphy Discussion Meeting in March 2024.

astro-ph.HE↗

arXiv2024

An Optically Targeted Search for Gravitational Waves emitted by Core-Collapse Supernovae during the Third Observing Run of Advanced LIGO and Advanced Virgo

We present the results from a search for gravitational-wave transients associated with core-collapse supernovae observed optically within 30 Mpc during the third observing run of Advanced LIGO and Advanced Virgo. No gravitational wave associated with a core-collapse supernova has been identified. We then report the detection efficiency for a variety of possible gravitational-wave emissions. For neutrino-driven explosions, the distance at which we reach 50% detection efficiency is up to 8.9 kpc, while more energetic magnetorotationally-driven explosions are detectable at larger distances. The distance reaches for selected models of the black hole formation, and quantum chromodynamics phase transition are also provided. We then constrain the core-collapse supernova engine across a wide frequency range from 50 Hz to 2 kHz. The upper limits on gravitational-wave energy and luminosity emission are at low frequencies down to $10^{-4}\,M_\odot c^2$ and $6 \times 10^{-4}\,M_\odot c^2$/s, respectively. The upper limits on the proto-neutron star ellipticity are down to 3 at high frequencies. Finally, by combining the results obtained with the data from the first and second observing runs of LIGO and Virgo, we improve the constraints of the parameter spaces of the extreme emission models. Specifically, the proto-neutron star ellipticities for the long-lasting bar mode model are down to 1 for long emission (1 s) at high frequency.

astro-ph.HE↗

arXiv2024

Exploring magnetic fields in merging galaxy: combining polarization and velocity gradient in the Centaurus Galaxy

In this study, we apply the Velocity Gradient Technique (VGT) to the merging Centaurus galaxy. We compare gradient maps derived from the PHANGS-ALMA survey using CO emission lines with magnetic field tracings from dust polarization data obtained via the HAWC+ instrument. Our analysis reveals a strong correspondence between the directions indicated by these two tracers across most of the galactic image. Specifically, we identify jet regions as areas of anti-alignment, consistent with previous reports that gradients tend to rotate 90 degrees in outflow regions. Statistically, we find that the alignment of magnetic fields, as revealed by polarization, is most accurate in regions with the highest signal-to-noise ratios. Our findings underscore the utility of velocity gradients as a valuable complementary tool for probing magnetic fields and dynamical processes in merging galaxies.

astro-ph.GA↗