Probing electromagnetic-gravitational wave emission coincidence in type I binary-driven hypernova family of long GRBs at very-high redshift

TL;DR

This paper uses cosmological time dilation to observe early X-ray emissions in high-redshift GRBs, validating the binary-driven hypernova model and exploring associated gravitational wave signals.

Contribution

It introduces a novel method leveraging time dilation to study early X-ray emissions in high-redshift GRBs, supporting the BdHN scenario and linking GRB types to neutron star progenitors.

Findings

Early X-ray emissions observed in GRBs at z=8.2, 9.4, and 4.61.

Validation of the collapse of CO core and νNS formation in BdHN scenario.

Possible gravitational wave signals from νNS spin transitions.

Abstract

The repointing time of the XRT instrument on the Neil Gehrels Swift Observatory satellite has posed challenges in observing and studying the early X-ray emissions within $\approx40$ s after a gamma-ray burst (GRB) trigger. To address this issue, we adopt a novel approach that capitalizes on the cosmological time dilation in GRBs with redshifts ranging from $3$ to $9$. Applying this strategy to Swift/XRT data, we investigate the earliest X-ray emissions of $368$ GRBs from the Swift catalog, including short and long GRBs. We compare the time delay between the GRB trigger and the initial Swift/XRT observation, measured in the GRB observer frame (OTD) and the cosmological rest-frame (RTD). This technique is here used in the analysis of GRB 090423 at $z=8.233$ (RTD $\sim8.2$ s), GRB 090429B at $z\approx9.4$ (RTD $\sim10.1$ s), and GRB 220101A at $z=4.61$ (RTD $\sim14.4$ s). The cosmological time dilation enables us to observe the very early X-ray afterglow emission in these three GRBs. We thus validate the observation of the collapse of the carbon-oxygen (CO) core and the coeval newborn neutron star ($\nu$NS) formation triggering the GRB event in the binary-driven hypernova (BdHN) scenario. We also evidence the $\nu$NS spin-up due to supernova ejecta fallback and its subsequent slowing down due to the X-optical-radio synchrotron afterglow emission. A brief gravitational wave signal may separate the two stages due to a fast-spinning $\nu$NS triaxial-to-axisymmetric transition. We also analyze the long GRB redshift distribution for the different BdHN types and infer that BdHNe II and III may originate the NS binary progenitors of short GRBs.