arXiv subjects

Divyajyoti

Publications and source records attributed to Divyajyoti.

13 recordsLinked to original sources

arXiv2026

LIGO A$^\sharp$: Detector Design and Science Prospects Beyond A+

We present the LIGO A$^\sharp$ detector concept, an upgrade for the LIGO observatories based on room-temperature interferometers beyond the fifth observing run (O5). Building on the A+ sensitivity, A$^\sharp$ targets broadband sensitivity improvements through heavier test masses, improved suspensions and seismic isolation, increased arm-cavity power, enhanced frequency-dependent squeezing, reduced coating thermal noise considering two scenarios, and improved control of mechanical motion and optical modes. We describe the principal design choices, projected noise performance, and corresponding astrophysical prospects. LIGO A$^\sharp$ substantially increases compact-binary detection rates, strengthens population inference, and improves both early-warning times and localization for binary neutron star mergers. The improved sensitivity enables more detailed studies of compact-binary coalescences, including higher-order multipoles, intermediate-mass black holes, remnant black hole ringdown, and the neutron star equation of state. It also broadens the discovery potential for new gravitational-wave sources such as continuous waves and bursts, should enable detection of the stochastic background from compact binary mergers if it remains undetected after O5, and strengthens the role of gravitational-wave detectors as probes of fundamental physics. We discuss key technical challenges and the role of A$^\sharp$ as both a major scientific upgrade for the 2030s and a technology pathfinder for next-generation gravitational-wave observatories, such as Cosmic Explorer.

astro-ph.IM↗

arXiv2026

Long-duration GW Searches for Sub-solar NSs and Superkilonovae using CoCoA

On 2025 August 18, the LIGO-Virgo-KAGRA collaboration reported a sub-threshold gravitational-wave (GW) candidate, S250818k, consistent with a binary neutron star (NS) merger potentially involving a sub-solar-mass compact object. Follow-up electromagnetic (EM) observations identified a Type IIb supernova, SN 2025ulz within the broad localization area of the GW signal. This potential link between a sub-solar GW event candidate and a Type IIb SN, while not confirmed given the low statistical significance of S250818k, has nonetheless sparked renewed interest in the "superkilonova" scenario, where sub-solar-mass NSs form through processes like the fragmentation of an accretion disk or core fission in a collapsing star. In this picture, the in-spiral and merger of a sub-solar NS-NS binary is followed by the merger of the NS-NS remnant with the central black hole (BH), producing chirp-like GW signals. For sub-solar NSs with masses in the (0.1-1)M_sun range and BH masses in the so-called lower mass gap range of ~(3-5) M_sun, these signals can persist in the 20 - 1024 Hz frequency band of ground-based GW detectors for (10^2-10^3)s, potentially offering an opportunity to probe the superkilonova scenario, as well as the lower mass gap between NSs and stellar-mass BHs. However, the complexity of the underlying astrophysics may yield waveforms that deviate from standard templates, limiting the use of matched filtering in real GW searches. We therefore explore the detectability of such signals using the Cross-Correlation Algorithm (CoCoA), a more robust though less sensitive cross-correlation method. We discuss general strategies for implementing CoCoA superkilonova searches via either targeted follow-up of candidate chirps identified in matched-filter searches, or EM-triggered searches of stripped-envelope core-collapse SNe.

astro-ph.HE↗

arXiv2026

Radio Follow Up of a Sub-threshold GRB in the Sky Localization Area of GW241125

Since the Fermi satellite's identification of a candidate $\gamma$-ray burst (GRB) temporally coincident with GW150914, several tentative, and often debated, associations between electromagnetic (EM) transients and gravitational-wave (GW) signals from binary black hole (BBH) mergers have been reported. One such event, S241125n (later confirmed as GW241125_010116), was identified during the fourth observing run (O4) of Advanced LIGO and found to be spatially (within large GW localization uncertainty) and temporally coincident with a subthreshold GRB detected by the Swift Burst Alert Telescope Gamma-ray Urgent Archiver for Novel Opportunities (BAT-GUANO). Here, we present results from a radio follow-up campaign targeting the BAT-GUANO localization region, carried out with the Karl G. Jansky Very Large Array (VLA). We also re-analyze Swift/XRT observations of the field, and combine these results with optical upper limits. Our analysis constrains the isotropic kinetic energy of a putative relativistic jet launched in the BBH merger to $\lesssim 3 \times 10^{50}$ erg for $n_{ISM} = 1.0 cm^{-3}$. We also discuss both the challenges and the diagnostic power of radio follow up in assessing candidate BBH-GRB associations, and present projections for analogous radio studies in the LIGO-Virgo-KAGRA observing run 5 (O5), and in the era of next-generation ground-based instrumentation. The enhanced sensitivity and localization capabilities of detector networks such as Cosmic Explorer and the Einstein Telescope, paired with the enhanced sensitivity of next-generation radio interferometers such as the next-generation VLA and the Square Kilometre Array, will significantly strengthen coordinated multi-messenger follow-up of BBHs. These next-generation facilities are likely to provide an answer to whether BBHs host relativistic ejecta powered by mini-disk accretion.

astro-ph.HE↗

arXiv2026

Mapping the star formation peak with LIGO A# and Next-Generation detectors

Measuring the redshift evolution of star formation rate density is crucial in understanding the origin and evolution of galaxies and large scale structure in the universe. It is currently measured with electromagnetic probes, however, these probes often track luminosity, which is then converted to star formation rate (SFR) depending on various factors such as initial mass function, dust extinction, etc. Gravitational waves provide an independent method to constrain SFR at high redshifts by tracking the redshift evolution obtained from analysis of binary black hole mergers. In this study we explore three population models for star-formation combined with an \textit{inverse} time-delay model and demonstrate that it is possible to obtain bounds on the peak of redshift distribution with a network of upgraded LIGO detectors (such as LIGO-A#). For a year of observation, using simulated signals with a merger rate peak at $z_\text{peak}=1.5$, a network of LIGO detectors at A# sensitivity is able to constrain the peak of merger rate with a precision of $\pm 0.1$. Further, we obtain the results with a next-generation network (of Cosmic Explorer and Einstein Telescope) and conclude that the redshift distribution will be extremely well measured, with a precision of $\pm 0.02$, with future detectors.

gr-qc↗

arXiv2025

Biased parameter inference of eccentric, spin-precessing binary black holes

While the majority of gravitational wave (GW) events observed by the LIGO and Virgo detectors are consistent with mergers of binary black holes (BBHs) on quasi-circular orbits, some events are also consistent with non-zero orbital eccentricity, indicating that the binaries could have formed via dynamical interactions. Moreover, there may be GW events which show support for spin-precession, eccentricity, or both. In this work, we study the interplay of spins and eccentricity on the parameter estimation of GW signals from BBH mergers. We inject eccentric signals with no spins, aligned spins, and precessing spins using hybrids, TEOBResumS-DALI, and new Numerical Relativity (NR) simulations, respectively, and study the biases in the posteriors of source parameters when these signals are recovered with a quasi-circular precessing-spin waveform model, as opposed to an aligned-spin eccentric waveform model. We find significant biases in the source parameters, such as chirp mass and spin-precession ($\chi_p$), when signals from highly-eccentric BBHs are recovered with a quasi-circular waveform model. Moreover, we find that for signals with both eccentricity and spin-precession effects, Bayes factor calculations confirm that an eccentric, aligned-spin model is preferred over a quasi-circular precessing-spin model. Our study highlights the complex nature of GW signals from eccentric, precessing-spin binaries and the need for readily usable inspiral-merger-ringdown eccentric, spin-precessing waveform models for unbiased parameter estimation.

gr-qc↗

arXiv2024

Inferring additional physics through unmodelled signal reconstructions

Parameter estimation of gravitational wave data is often computationally expensive, requiring simplifying assumptions such as circularisation of binary orbits. Although, if included, the sub-dominant effects like orbital eccentricity may provide crucial insights into the formation channels of compact binary mergers. To address these challenges, we present a pipeline strategy leveraging minimally modelled waveform reconstruction to identify the presence of eccentricity in real time. Using injected signals, we demonstrate that ignoring eccentricity ($e_{\rm 20Hz} \gtrsim 0.1$) leads to significant biases in parameter recovery, including chirp mass estimates falling outside the 90% credible interval. Waveform reconstruction shows inconsistencies increase with eccentricity, and this behaviour is consistent for different mass ratios. Our method enables low-latency inferences of binary properties supporting targeted follow-up analyses and can be applied to identify any physical effect of measurable strength.

gr-qc↗

arXiv2024

ESIGMAHM: An Eccentric, Spinning inspiral-merger-ringdown waveform model with Higher Modes for the detection and characterization of binary black holes

We present a time-domain inspiral-merger-ringdowm (IMR) waveform model ESIGMAHM constructed within a framework we named ESIGMA for coalescing binaries of spinning black holes on moderately eccentric orbits (Huerta et al. (2018) [Phys. Rev. D 97, 024031]). We now include the effect of black hole spins on the dynamics of eccentric binaries, as well as model sub-dominant waveform harmonics emitted by them. The inspiral evolution is described by a consistent combination of latest results from post-Newtonian theory, self-force, and black hole perturbation theory. We assume that these moderately eccentric binaries radiate away most of their orbital eccentricity before merger, and seamlessly connect the eccentric inspiral with a numerical relativity based surrogate waveform model for mergers of spinning binaries on quasi-circular orbits. We validate ESIGMAHM against eccentric Numerical Relativity simulations, and also against contemporary effective-one-body and phenomenological models in the quasi-circular limit. We find that ESIGMAHM achieves match values greater than $99\%$ for quasi-circular spin-aligned binaries with mass ratios up to $8$, and above $97\%$ for non-spinning and spinning eccentric systems with small or positively aligned spins. Using IMRESIGMA, we quantify the impact of orbital eccentricity on GW signals, showing that next-generation detectors can detect eccentric sources up to $10\%$ louder than quasi-circular ones. We also show that current templated LIGO-Virgo searches will lose more than $10\%$ of optimal SNR for about $20\%$ of all eccentric sources by using only quasi-circular waveform templates. The same will result in a $25\%$ loss in detection rate for eccentric sources with mass ratios $m_1/m_2\geq 4$. Our results highlight the need for including eccentricity and higher-order modes in GW source models and searches for asymmetric eccentric BBH signals.

gr-qc↗

arXiv2024

Synergies in analysing binary black hole mergers: Effect of orbital eccentricity, spin-precession, and non-quadrupole modes

A gravitational wave (GW) signal carries imprints of the properties of its source. The ability to extract source properties crucially depends on our prior knowledge of the signal morphology. Even though binary black hole (BBH) mergers are the cleanest system to model in general relativity, currently, there are no waveform models which include all physical effects. This thesis focuses on three subdominant effects: orbital eccentricity, spin-precession, and non-quadrupole or higher-order modes (HMs). We study the interplay of these effects on data analysis of GW signals, highlighting the shortcomings and emphasizing the need for more advanced waveforms. For instance, we investigate whether orbital eccentricity and spin-precession can mimic each other and thus caution the GW community towards the biases that may arise due to the neglect of eccentricity and/or spins in the waveform models. Using waveforms with full spin-precession and HMs, we extend the existing spin-induced quadrupole moment (SIQM) test - a null test to distinguish BBH systems from other black hole mimickers - and show that these improved waveforms give significantly better bounds. Additionally, we quantify the parameter space where the effect of HMs is most significant and show the importance of detecting these modes in GW events for future ground-based GW detectors such as Cosmic Explorer and Einstein Telescope.

gr-qc↗

arXiv2023

Effect of double spin-precession and higher harmonics on spin-induced quadrupole moment measurements

We investigate the prospect of performing a null test of binary black hole (BBH) nature using spin-induced quadrupole moment (SIQM) measurements. This is achieved by constraining a deviation parameter ($\delta\kappa$) related to the parameter ($\kappa$) that quantifies the degree of deformation due to the spin of individual binary components on leading (quadrupolar) spin-induced moment. Throughout the paper, we refer to $\kappa$ as the SIQM parameter and $\delta\kappa$ as the SIQM-deviation parameter. The test presented here extends the earlier SIQM-based null tests for BBH nature by employing waveform models that account for double spin-precession and higher modes. We find that waveform with double spin-precession gives better constraints for $\delta\kappa$, compared to waveform with single spin-precession. We also revisit earlier constraints on the SIQM-deviation parameter for selected GW events observed through the first three observing runs (O1-O3) of LIGO-Virgo detectors. Additionally, the effects of higher-order modes on the test are also explored for a variety of mass-ratio and spin combinations by injecting simulated signals in zero-noise. Our analyses indicate that binaries with mass-ratio greater than 3 and significant spin precession may require waveforms that account for spin-precession and higher modes to perform the parameter estimation reliably.

gr-qc↗

arXiv2023

Blind spots and biases: the dangers of ignoring eccentricity in gravitational-wave signals from binary black holes

Most gravitational wave (GW) events observed by the LIGO and Virgo detectors are consistent with mergers of binary black holes (BBHs) on quasi-circular orbits. However, some events are also consistent with non-zero orbital eccentricity, which can indicate that the binary formed via dynamical interactions. Active GW search pipelines using quasi-circular waveform templates are inefficient for detecting eccentric mergers. Also, analysing eccentric GW signals with waveform models neglecting eccentricity can lead to biases in the recovered parameters. We explore the detectability and characterisation of eccentric signals when searches and analyses rely on quasi-circular waveform models. We find that for a reference eccentric population, the fraction of events having fitting factor (FF) $< 0.95$ can be up to $\approx 2.2\%$ compared to $\approx 0.4\%$ for the baseline population. This leads to the loss in signal recovery fraction for up to $6\%$ for parameter space with non-negligible eccentricity ($e_{10} > 0.01$) and high mass ratio ($q > 3$). We perform parameter estimation (PE) for non-spinning and aligned-spin eccentric GW injections from BBHs with a total mass $M=35 M_\odot$, based on numerical relativity simulations and an EOB based inspiral-merger-ringdown model (TEOBResumS). We recover these injections using both quasi-circular and eccentric waveform models. For cases with $e_{20} \sim 0.1$, quasi-circular models fail to estimate chirp mass within the 90% credible interval accurately. Further, for these low-mass injections, spin-induced precession does not mimic eccentricity. For injections of $e_{20}\sim 0.1$, PE conducted with an inspiral-only eccentric waveform model correctly characterises the injected signal to within 90% confidence, and recovers the injected eccentricities, suggesting that such models are sufficient for characterisation of low-mass eccentric BBH. (abridged)

gr-qc↗

arXiv2022

High accuracy post-Newtonian and numerical relativity comparisons involving higher modes for eccentric binary black holes and a dominant mode eccentric inspiral-merger-ringdown model

Spherical harmonic modes of gravitational waveforms for inspiraling compact binaries in eccentric orbits from post-Newtonian (PN) theory accurate to third post-Newtonian order, and those extracted from numerical relativity (NR) simulations for binary black holes (BBHs) are compared. We combine results from the two approaches (PN and NR) to construct time-domain hybrid waveforms that describe the complete evolution of BBH mergers through inspiral-merger-ringdown (IMR) stages. These hybrids are then used in constructing a fully analytical dominant mode ($\ell$=2, $|m|$=2) eccentric IMR model. A simple extension to a multi-mode model based on this dominant mode model is also presented. Overlaps with quasi-circular IMR waveform models including the effect of higher modes, maximized over a time- and phase-shift, hint at the importance (mismatches $>1\%$) of including eccentricity in gravitational waveforms when analysing BBHs lighter than $\sim 80 M_{\odot}$, irrespective of the binary's eccentricity (as it enters the LIGO bands), or mass-ratio. Combined impact of eccentricity and higher modes seems to become more apparent through smaller overlaps with increasing inclination angles and mass ratios. Additionally, we show that the state-of-the-art quasi-circular models including the effect of higher modes will not be adequate in extracting source properties for signals with initial eccentricities $e_0$ $\gtrsim0.1$.

gr-qc↗

arXiv2022

Improved early-warning estimates of luminosity distance and orbital inclination of compact binary mergers using higher modes of gravitational radiation

The pre-merger (early-warning) gravitational-wave (GW) detection and localization of a compact binary merger would enable astronomers to capture potential electromagnetic (EM) emissions around the time of the merger, thus shedding light on the complex physics of the merger. While early detection and sky localization are of primary importance to the multimessenger follow-up of the event, improved estimates of luminosity distance and orbital inclination could also provide insights on the observability of the EM emission. In this work, we demonstrate that the inclusion of higher modes of gravitational radiation, which vibrate at higher multiples of the orbital frequency than the dominant mode, would significantly improve the earlywarning estimates of the luminosity distance and orbital inclination of the binary. This will help astronomers to better determine their follow-up strategy. Focusing on future observing runs of the ground-based GW detector network [O5 run of LIGOVirgo-KAGRA, Voyager, and third-generation (3G) detectors], we show that for a range of masses spanning the neutron-star black-hole binaries that are potentially EM-bright, the inclusion of higher modes improve the luminosity distance estimates by a factor of ~ 1 - 1.5 (1.1 - 2) [1.1 - 5] for the O5 (Voyager) [3G] observing scenario, 45 (45) [300] seconds before the merger for the sources located at 100 Mpc. There are significant improvements in orbital inclination estimates as well. We also investigate these improvements with varying sky-location and polarization angle. Combining the luminosity distance uncertainties with localization skyarea estimates, we find that the number of galaxies within localization volume is reduced by a factor of ~ 1 - 2.5 (1.2 - 4) [1.2 - 10] with the inclusion of higher modes at early-warning time of 45 (45) [300] seconds in O5 (Voyager) [3G].

astro-ph.HE↗

arXiv2021

Detectability of gravitational higher order modes in the third-generation era

Detection of higher order modes of gravitational waves in third-generation (3G) ground-based detectors such as Cosmic Explorer and Einstein Telescope is explored. Using the astrophysical population of binary black holes based on events reported in the second gravitational wave catalog by Laser Interferometer Gravitational Wave Observatory (LIGO) and Virgo (GWTC-2), in conjunction with the Madau-Dickinson model for redshift evolution of the binary black hole mergers, we assess the detectability of these higher order modes using a network consisting of three third-generation detectors. We find that the two subleading modes [(3,3) and (4,4)] can be detected in approximately 30% of the population with a network signal-to-noise ratio of 3 or more, and for nearly 10% of the sources, the five leading modes will be detectable. Besides, a study concerning the effect of binary's mass ratio and its orbital inclination with the observer's line-of-sight in detecting various modes is presented. For a few selected events of the LIGO-Virgo catalog, we identify the modes that would have been detected if a third-generation detector was operational when these events were recorded. We also compute the detectability of higher modes by Voyager and find that only $\sim$ 6 and 2% of the detectable population will have an associated detection of (3,3) and (4,4) modes, respectively. Observing these higher order modes in the 3G era would have a huge impact on the science possible with these detectors ranging from astrophysics and cosmology to testing strong-field gravity.

gr-qc↗