Probing anisotropies of gravitational-wave backgrounds with a space-based interferometer III: Reconstruction of a high-frequency skymap

TL;DR

This paper introduces a numerical method for reconstructing high-frequency gravitational-wave background skymaps using space-based interferometer data, demonstrating potential angular resolutions and effects of noise.

Contribution

It presents a new numerical scheme for high-frequency GWB skymap reconstruction from cross-correlation data, applicable to space-based interferometers like LISA.

Findings

Reconstruction is feasible for frequencies above $f_*$ with high angular resolution.

Instrumental noise limits the resolution to multipoles $\, ext{l}\, extless 7$ for S/N > 5.

The method effectively maps anisotropic GWBs using planned space interferometers.

Abstract

We develop a numerical scheme to make a high-frequency skymap of gravitational-wave backgrounds (GWBs) observed via space-based interferometer. Based on the cross-correlation technique, the intensity distribution of anisotropic GWB can be directly reconstructed from the time-ordered data of cross-correlation signals, with full knowledge of detector's antenna pattern functions. We demonstrate how the planned space interferometer, LISA, can make a skymap of GWB for a specific example of anisotropic signals. At the frequency higher than the characteristic frequency $f_*=1/(2\pi L)$, where $L$ is the arm-length of the detector, the reconstructed skymap free from the instrumental noise potentially reaches the angular resolution up to the multipoles $\ell\sim10$. The presence of instrumental noises degrades the angular resolution. The resultant skymap has angular resolution with multipoles $\ell\leq 6\sim7$ for the anisotropic signals with signal-to-noise ratio S/N$>5$.