arXiv subjects

Sumedha Biswas

Publications and source records attributed to Sumedha Biswas.

3 recordsLinked to original sources

arXiv2026

Identifying Host Galaxies of Binary Black Hole Mergers with Next-Generation Gravitational Wave Detector Networks

Identifying the host galaxy of a binary black hole (BBH) merger detected via gravitational waves (GWs) remains a challenge due to the absence of electromagnetic counterparts and the large localization volumes produced by current-generation detectors. A confident host association would provide stellar population properties to constrain BBH formation channels and enable measurements of cosmological parameters such as the Hubble constant, H0. We simulate BBH mergers in nearby (z<0.25) host galaxies to evaluate the feasibility of host identification with future GW detector networks, including configurations with the planned LIGO-India detector and third-generation detectors such as the Einstein Telescope (ET) and Cosmic Explorer (CE). We construct two injection grids to explore variations in BBH mass, distance, and directional sensitivity, and infer localization volumes using the Fisher Information Matrix (FIM)-based parameter estimation implemented through BILBY. To assess the prospects for unique host identification, we introduce a set of diagnostics: theoretical comoving volume thresholds for galaxies of a given stellar mass, derived from galaxy stellar mass functions, a metallicity-based volume threshold motivated by progenitor environment models, stellar mass fractions to quantify candidate host prominence, and the probability of chance alignment (p_c). These metrics provide ways to evaluate host associations and constrain BBH formation channels. We find that future networks that include ET and CE localize BBH mergers to volumes smaller than those theoretical thresholds, implying potentially unique host identification, out to ~1000 Mpc at a rate of ~100 yr^{-1}. While associations for individual events may remain uncertain, our framework is well-suited to population-level analyses, enabling constraints on BBH formation scenarios in the era of next-generation GW detector networks.

astro-ph.HE↗

arXiv2025

Comparing the Space Densities of Millisecond-Spin Magnetars and Fast X-Ray Transients

Fast X-ray transients (FXTs) are bright X-ray flashes with durations of minutes to hours, peak isotropic luminosities of L_X,peak ~ 10^42-10^47 erg/s, and total isotropic energies of E ~ 10^47-10^50 erg. They have been detected in the soft X-ray band by Chandra, XMM-Newton, Swift-XRT, and, most recently, by Einstein Probe, which has reported more than 50 FXTs in its first year of operation. While several models have been proposed, the nature of many FXTs remains unknown. One model suggests FXTs are powered by the spin-down of newly formed millisecond magnetars, typically produced by binary neutron star (BNS) mergers. However, the BNS volumetric rate, ~10^2 Gpc^-3 yr^-1, barely overlaps with the estimated FXT rate of 10^3-10^4 Gpc^-3 yr^-1. Even within that overlap, BNS mergers would need to produce FXTs at nearly 100% efficiency. We explore whether other millisecond magnetar formation channels could account for this discrepancy. We compile rate densities for several proposed progenitors: accretion-induced collapse of white dwarfs, binary white dwarf mergers, neutron star-white dwarf mergers, and the collapse of massive stars, and convert Galactic event rates into volumetric rates using either the star formation rate or the stellar mass density distributions as a function of redshift. We find that the highest potential formation rates arise from binary white dwarf mergers and massive star collapses. However, both channels face theoretical and observational challenges: the spin and magnetic field properties of the resulting neutron stars are uncertain, and few are expected to satisfy both conditions required for FXT production. Across all scenarios, the fraction of suitable millisecond magnetars is low or poorly constrained. We conclude that they are unlikely to be the dominant progenitors of FXTs and can contribute to at most 10% of the observed FXT population.

astro-ph.HE↗

arXiv2023

Preparing for Gaia Searches for Optical Counterparts of Gravitational Wave Events during O4

The discovery of gravitational wave (GW) events and the detection of electromagnetic counterparts from GW170817 has started the era of multimessenger GW astronomy.The field has been developing rapidly and in this paper,we discuss the preparation for detecting these events with the ESA Gaia satellite,during the 4th observing run of the LIGO-Virgo-KAGRA (LVK) collaboration that has started on May 24,2023. Gaia is contributing to the search for GW counterparts by a new transient detection pipeline called GaiaX. In GaiaX, a new source appearing in the field of view of only one of the two telescopes on-board Gaia is sufficient to send out an alert on the possible detection of a new transient. Ahead of O4, an experiment was conducted over a period of about two months. During the two weeks around New Moon in this period of time, the MeerLICHT (ML) telescope located in South Africa tried (weather permitting) to observe the same region of the sky as Gaia within 10 minutes. Any GaiaX detected transient was published publicly. ML and Gaia have similar limiting magnitudes for typical seeing conditions at ML. At the end of the experiment, we had 11861 GaiaX candidate transients and 15806 ML candidate transients, which we further analysed and the results of which are presented in this paper. Finally, we discuss the possibility and capabilities of Gaia contributing to the search for electromagnetic counterparts of gravitational wave events during O4 through the GaiaX detection and alert procedure.

astro-ph.HE↗