arXiv subjects

Mukesh Kumar Singh

Publications and source records attributed to Mukesh Kumar Singh.

11 recordsLinked to original sources

arXiv2026

Gravitational Wave Informed Inference of 21-cm Global Signal Parameters

Understanding how and when the first stars and galaxies formed remains one of the central challenges in modern cosmology. These structures emerged during the transition from the Dark Ages to the Cosmic Dawn, a period that remains observationally unconstrained despite strong theoretical progress. During this epoch, neutral hydrogen absorbed a fraction of cosmic microwave background photons through its 21-cm hyperfine transition, producing a 21-cm absorption signal whose evolution encodes the early Universe's thermal and ionization history. However, extracting the underlying astrophysical parameters from this signal is limited by severe parameter degeneracies, which cannot be resolved without independent observational probes. The next-generation gravitational wave (GW) detectors, such as Cosmic Explorer (CE), will observe binary black hole (BBH) mergers up to very large redshifts and hence will detect a fraction of them formed within the redshift range $\sim 13-25$. The merger rate of these BBHs will depend on the star formation rate density (SFRD) at these redshifts, together with the BBH formation efficiency and a time delay distribution. Therefore, the merger rate of these BBHs can work as a tracer of the SFRD in the redshift range $\sim 13-25$. In this Letter, we establish a novel multi-messenger framework and present a proof-of-principle concept of how the observations of BBH mergers form next-generation GW detectors can improve the inference of parameters generating the 21-cm cosmic hydrogen signal, and help break degeneracies between them.

astro-ph.CO↗

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

Observability of eccentricity in a population of merging compact binaries

We investigate the prospects of observing residual eccentricity in a population of compact binaries by calculating the power in the eccentric harmonics, following the methodology in arXiv:2411.04187. Although most observed compact binary coalescences are expected to circularize before entering the sensitivity band of the ground-based gravitational-wave (GW) detectors, dynamical interactions in dense star clusters can lead to a fraction of these binaries with non-negligible eccentricity at the time of detection. To quantify the observability of eccentricity, we simulate a population of merging compact binaries and identify those which have sufficient power in sub-dominant eccentric harmonics to be clearly distinguishable from quasi-circular systems. We consider a binary black hole (BBH) population derived from globular cluster simulations with residual eccentricity distribution obtained from Cluster Monte Carlo (CMC) catalogs as well as a fiducial log-uniform model. Assuming the LIGO-Virgo network of GW detectors with their sensitivities achieved during LIGO-Virgo-KAGRA (LVK) Observing Run (O4), we find that the BBH population with measurable eccentricity will have a significantly higher median eccentricity $e_{\mathrm{10Hz}}\sim 0.3$ (with $90\%$ range: $0.1 - 0.5$) and signal-to-noise ratio (SNR) $\sim 20$ ($90\%$ range: $13 - 57$) compared to the observable population of BBHs. We compare our predictions of the regions of parameter space where eccentricity is detectable with the claimed observations of eccentricity in GW events from third Gravitational Wave Transient Catalog (GWTC-3).

astro-ph.HE↗

arXiv2025

Early Warning From Eccentric Compact Binaries: Template Initialization And Sub-dominant Mode Effects

Early warning of gravitational waves (GWs) is essential for multi-messenger observations of binary neutron star and black hole-neutron star merger events. In this study, we investigate early warning prospects from eccentric compact binaries, whose mergers are expected to comprise a significant fraction of detected GW events in the future. Eccentric binaries exhibit oscillatory frequency evolution, causing GW frequencies to recur multiple times through their coalescence. Consequently, generating eccentric waveform templates for early warning requires specification of initial conditions. While the standard approach involves initiating waveform generation when the orbit-averaged frequency enters the detector band, we compare this with an alternative approach that uses the periastron frequency as the starting point. Our analysis shows that initializing at the periastron frequency yields an improved signal-to-noise ratio and sky localization. Additionally, including subdominant modes alongside the dominant $(2,2)$ mode leads to further improvements in sky localization. We explore the parameter space of primary mass $m_1 \in [1.4, 15] \, M_\odot$, spin $χ_1 \in [0, 0.8]$, and eccentricity $e \leq 0.4$ across three detector configurations: O5, Voyager, and 3G. We find that in the O5 (Voyager) configuration, including eccentricity and subdominant modes, the sky localization area can be reduced by $2-80\% (2-85\%)$ at 1000 sq. deg. with increasing eccentricity from $e_5 = 0.1$ to $e_5 = 0.4$, yielding up to $41$ seconds (1 minute) of extra early warning time. For NSBH systems, subdominant modes contribute up to $70$ $(94)\%$ reduction for O5 (Voyager) scenario. In the 3G detector scenario, the sky area reduction due to eccentricity reaches $80\%$ (from $e_{2.5} = 0.1$ to $e_{2.5} = 0.4$) at 100 sq. deg., and subdominant modes enhance the reduction up to $98\%$ for NSBH systems.

gr-qc↗

arXiv2024

Impact of higher harmonics of gravitational radiation on the population inference of binary black holes

Templates modeling just the dominant mode of gravitational radiation are generally sufficient for the unbiased parameter inference of near-equal-mass compact binary mergers. However, neglecting the subdominant modes can bias the inference if the binary is significantly asymmetric, very massive, or has misaligned spins. In this work, we explore if neglecting these subdominant modes in the parameter estimation of non-spinning binary black hole mergers can bias the inference of their population-level properties such as mass and merger redshift distributions. Assuming the design sensitivity of advanced LIGO-Virgo detector network, we find that neglecting subdominant modes will not cause a significant bias in the population inference, although including them will provide more precise estimates. This is primarily due to the fact that asymmetric binaries are expected to be rarer in our detected sample, due to their intrinsic rareness and the observational selection effects. The increased precision in the measurement of the maximum black hole mass can help in better constraining the upper mass gap in the mass spectrum.

gr-qc↗

arXiv2023

Associating fast radio bursts with compact binary mergers via gravitational lensing

The origin of fast radio bursts (FRBs) is currently an open question with several proposed sources and corresponding mechanisms for their production. Among them are compact binary coalescences (CBCs) that also generate gravitational waves (GWs). Spatial and temporal coincidences between GWs and FRBs have so far been used to search for potential FRB counterparts to GWs from CBCs. However, such methods suffer from relatively poor sky-localisation of the GW sources, and similarly poor luminosity distance estimates of both GW and FRB sources. The expected time delay between the GW and radio emission is also poorly understood. In this work, we propose an astrophysical scenario that could potentially provide an unambiguous association between CBCs and FRBs, if one exists, or unambiguously rule out FRB counterparts to a given CBC GW event. We demonstrate that, if a CBC that emitted both GWs and FRBs, is gravitationally lensed, we can make a $> 5σ$ association using time-delay estimates of the lensed GW and FRB images (in strong lensing), which are expected to be measured with mili-second (for GW) and nano-second (FRB) precisions. We also demonstrate that the CBC-FRB association can be made in the microlensing regime as well where wave-optics effects modulate the GW waveform. We further investigate the rate of such detected associations in future observing scenarios of both GW and radio detectors.

astro-ph.HE↗

arXiv2023

Gear-up for the Action Replay: Leveraging Lensing for Enhanced Gravitational-Wave Early-Warning

Pre-merger gravitational-wave (GW) sky-localisation of binary neutron star (BNS) and neutron star black hole (NSBH) coalescence events, would enable telescopes to capture precursors and electromagnetic (EM) emissions around the time of the merger. We propose a novel astrophysical scenario that could provide early-warning times of hours to days before coalescence with sub-arcsecond localisation, provided that these events are gravitationally lensed. The key idea is that if the BNS/NSBH is lensed, then so must the host galaxy identified via the EM counterpart. From the angular separation of the lensed host galaxy images, as well as its redshift and the (foreground) lens redshift, we demonstrate that we can predict the time delays assuming a standard lens model. Encouraged by the non-trivial upper limits on the detection rates of lensed BNS/NSBH mergers that we estimate for upcoming observing runs of the LIGO-Virgo-Kagra and third generation networks, we assess the feasibility and benefits of our method. To that end, we study the effect of limited angular resolution of the telescopes on our ability to predict the time delays. We find that with an angular resolution of $0.05''$, we can predict time delays of $> 1$ day with $1σ$ error-bar of $\mathcal{O}$(hours) at best. We also construct realistic time delay distributions of detectable lensed BNSs/NSBHs to forecast the early-warning times we might expect in the observing scenarios we consider.

astro-ph.HE↗

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

Improved early warning of compact binary mergers using higher modes of gravitational radiation: A population study

A gravitational-wave (GW) early-warning of a compact-binary coalescence event, with a sufficiently tight localisation skymap, would allow telescopes to point in the direction of the potential electromagnetic counterpart before its onset. This will enable astronomers to extract valuable information of the complex astrophysical phenomena triggered around the time of the merger. Use of higher-modes of gravitational radiation, in addition to the dominant mode typically used in templated real-time searches, was recently shown to produce significant improvements in early-warning times and skyarea localisations for a range of asymmetric-mass binaries. In this work, we perform a large-scale study to assess the benefits of this method for a population of compact binary merger observations. In particular, we inject 100,000 such signals in Gaussian noise, with component masses $m_1 \in \left[1, 60 \right] M_{\odot}$ and $m_2 \in \left [1, 3 \right] M_{\odot}$. We consider three scenarios involving ground-based detectors: the fifth (O5) observing run of the Advanced LIGO-Virgo-KAGRA network, its projected Voyager upgrade, as well as a proposed third generation (3G) network. We find that for fixed early warning times of $20-60$ seconds, the inclusion of the higher modes can provide localisation improvements of a factor of $\gtrsim 2$ for up to $\sim 60\%$ ($70 \%$) of the neutron star-black hole systems in the O5 (Voyager) scenario. Considering only those neutron star-black hole systems which can produce potential electromagnetic counterparts, such improvements in the localisation can be expected for $\sim 5-35\%$ $(20-50\%)$ binaries in O5 (Voyager), although the localisation areas themselves depend on the distances. For the 3G scenario, a significant fraction of the events have time gains of a minute to several minutes, assuming fiducial target localisation areas of 100 to 1000 sq. deg.

astro-ph.HE↗

arXiv2020

Of Harbingers and Higher Modes: Improved gravitational-wave early-warning of compact binary mergers

A crucial component to maximizing the science gain from the multi-messenger follow-up of gravitational-wave (GW) signals from compact binary mergers is the prompt discovery of the electromagnetic counterpart. Ideally, the GW detection and localization must be reported early enough to allow for telescopes to slew to the location of the GW-event before the onset of the counterpart. However, the time available for early warning is limited by the short duration spent by the dominant ($\ell = m = 2$) mode within the detector's frequency band. Nevertheless, we show that, including higher modes - which enter the detector's sensitivity band well before the dominant mode - in GW searches, can enable us to significantly improve the early warning ability for compact binaries with asymmetric masses (such as neutron-star-black-hole binaries). We investigate the reduction in the localization sky-area when the $\ell = m = 3$ and $\ell = m = 4$ modes are included in addition to the dominant mode, considering typical slew-times of electromagnetic telescopes ($30-60$ sec). We find that, in LIGO's projected "O5" ("Voyager") network with five GW detectors, some of the neutron-star-black-hole mergers, located at a distance of $40$ Mpc, can be localized to a few hundred sq. deg. $\sim 45$ sec prior to the merger, corresponding to a reduction-factor of $3-4$ ($5-6$) in sky-area. For a third-generation network, we get gains of up to 1.5 minutes in early warning times for a localization area of $100$ sq. deg., even when the source is placed at $100$ Mpc.

astro-ph.HE↗

arXiv2010

Node Isolation Probability of Wireless Adhoc Networks in Nagakami Fading Channel

This paper investigates the issue of connectivity of a wireless adhoc network in the presence of channel impairments. We derive analytical expressions for the node isolation probability in an adhoc network in the presence of Nakagami-m fading with superimposed lognormal shadowing. The node isolation probability is the probability that a randomly chosen node is not able to communicate with none of the other nodes in the network. An extensive investigation into the impact of path loss exponent, lognormal shadowing, Nakagami fading severity index, node density, and diversity order on the node isolation probability is conducted. The presented results are beneficial for the practical design of ad hoc networks.

cs.NI↗