Prospects of calibrating afterglow modeling of short GRBs with gravitational wave inclination angle measurements and resolving the Hubble tension with a GW-GRB association event

TL;DR

This paper explores how gravitational wave inclination angle measurements can calibrate short GRB afterglow models and potentially resolve the Hubble tension, emphasizing the importance of joint GW-GRB observations for cosmology.

Contribution

It demonstrates the feasibility of calibrating afterglow models using GW inclination angles and assesses the potential to resolve the Hubble tension with single GW-GRB events.

Findings

Inclination angles can be measured within 0.1 rad for certain BNS mergers.

Energetic off-axis GRBs may be detectable at 100-200 Mpc distances.

A 3% Hubble constant precision is possible with well-constrained viewing angles.

Abstract

In the numerical modeling of the GRB afterglow, some approximations have been made for simplicity, and different groups developed their codes. A robust test of these models/approaches is challenging because of the lack of directly measured physical parameters. Fortunately, the viewing angle inferred from the afterglow modeling is widely anticipated to be the same as the inclination angle of the binary neutron star (BNS) mergers that can be evaluated with the gravitational wave (GW) data. Therefore in the future, it is possible to calibrate the afterglow modeling with the GW inclination angle measurements. We take three methods, including both analytical estimations and direct simulations, to project the uncertainties of the inclination angle measurements. For some BNS mergers accompanied with electromagnetic counterparts detected in the O4/O5 runs of LIGO/Virgo/KAGRA/LIGO-India detectors, we show that the inclination angle can be determined within an uncertainty of $\leq 0.1$ rad, supposing that the Hubble constant is known with an accuracy of $\leq 3\%$ and the uncertainty of Hubble flow velocity is within $\sim 1 \%$. The off-axis GRB outflow will give rise to afterglow emission, and the most energetic ones may be detectable at the distance of $\sim$ 100-200 Mpc even for a viewing angle of $\geq 0.3$ rad. Such events can thus serve as a robust test of the afterglow modeling approach. We have also evaluated the prospect of resolving the so-called Hubble tension with a single GW/GRB association event. We find out that a $\sim 3\%$ precision Hubble constant is obtainable if the uncertainty of the viewing angle can be constrained to be within $\sim 0.1$ rad, which is expected to be the case for some nearby ($\leq 250$ Mpc) bright/on-axis GRBs with a well-behaved afterglow light curve displaying a clear achromatic break at early times.