Yugesh Bhoge | Searcharxiv

arXiv2026

Constraining equation of state of neutron star using neutron star-black hole mergers

In this work, we study tidal effects that can be observed in gravitational wave transient from neutron star-black hole (NSBH) mergers. It has been well known that neutron star's tidal deformation has imprint of equation of state and hence composition of neutron star matter. Compared to binary neutron star mergers, where we observe a combined effect of two neutron stars by measuring the parameter known as lambda tilde. In neutron star black hole mergers, we measure the tidal deformability of the neutron star component clearly. In this work, we study the feasibility of measuring the bare tidal deformability of a neutron star with planned gravitational detectors in the near and far future. We use the parameter estimation computation framework, Bilby is used to perform Bayesian inference for hundreds of NSBH mergers in current and future GW detector networks and obtain the posterior probability distribution functions of binary parameters. We find that we need at least 20 events to clearly distinguish the equation state of neutron stars in future detectors, including the Einstein Telescope and Cosmic Explorer.

gr-qc↗

arXiv2026

Distinguishing Kilonovae from Binary Neutron Star and Neutron Star-Black Hole Mergers

Kilonovae (KNe) are most informative when accompanied by a gravitational-wave signal, which can help identify the source as a binary neutron star (BNS) or a neutron star-black hole (NSBH) merger. However, future events will also be discovered serendipitously or through follow-up of other transients, without a confident identification of the progenitor. We ask whether the KN light curve alone can distinguish between these two progenitor channels. Using simulated BNS and NSBH populations together with semi-analytic light curve models, we compare their post-peak evolution across the optical $ugrizy$ bands, and quantify the separation between the two classes in each band with the area under the receiver-operating-characteristic curve (AUC). BNS and NSBH KNe populate distinct regions of the post-peak decline distribution, with BNS KNe fading faster in every band. The separation is cleanest in the blue $u$ and $g$ bands $5$ days after peak and in the redder $i$ band $10$ days after peak. Within $5$ days of peak, BNS KNe decline by $\gtrsim 6$ ($\gtrsim 4$) mag in $u$ ($g$) bands, whereas NSBH KNe fade by only $\sim 3$ ($\sim 1$) mag. Over $10$ days in $i$, NSBH KNe decline by $\sim 1$--$2$ mag against $\sim 3$--$6$ mag for BNS. We attribute this to the higher opacity of NSBH ejecta, which lengthens the photon-diffusion time and slows the decline in all bands, while a low opacity blue component drives the rapid early peak and decline of BNS KNe. Although the precise overlap is model-dependent, the qualitative separation persists across variations in the astrophysical population, the NS equation of state, and the controlled variation of ejecta model parameters, establishing the post-peak photometric decline as a viable EM-only diagnostic of whether a KN arose from a BNS or an NSBH merger.

astro-ph.HE↗