# Probing cosmic anisotropy with GW/FRB as upgraded standard sirens

## TL;DR

This paper demonstrates that combined GW/FRB observations as upgraded standard sirens significantly improve the sensitivity to cosmic anisotropy testing compared to using GW data alone, both theoretically and through simulations.

## Contribution

It introduces a novel approach of using combined GW/FRB data as upgraded standard sirens to enhance tests of cosmic anisotropy.

## Key findings

- Combined GW/FRB measurements double the sensitivity to cosmic anisotropy.
- Theoretical analysis confirms improved anisotropy constraints.
- Simulations support the effectiveness of the combined method.

## Abstract

Recently it was shown that cosmic anisotropy can be well tested using either standard siren measurement of luminosity distance $d_\mathrm{L}(z)$ from gravitational-wave (GW) observation or dispersion measure ($\mathrm{DM}(z)$) from fast radio burst (FRB). It was also observed that the combined measurement of $d_\mathrm{L}(z)\cdot\mathrm{DM}(z)$ from the GW/FRB association system as suggested in some of FRB models is more effective to constrain cosmological parameters than $d_\mathrm{L}(z)$ or $\mathrm{DM}(z)$ separately due to its independence from Hubble constant. In this paper, we will show both theoretically and with simulation that, this upgraded sirens from combined GW/FRB observations could test cosmic anisotropy with a double relative sensitivity compared to the usual standard siren from GW observation alone.