Maximum likelihood map-making with the Laser Interferometer Space Antenna

TL;DR

This paper introduces a maximum likelihood map-making algorithm for the Laser Interferometer Space Antenna (LISA) to reconstruct gravitational-wave background anisotropies, enabling better understanding of sky sensitivity and signal properties.

Contribution

The paper develops a novel optimal quadratic estimator-based map-maker for LISA, capable of reconstructing GWB anisotropies across different angular scales and frequencies.

Findings

LISA can probe anisotropies up to angular scale $\,\ell_{\rm max} \lesssim 15$.

The map-maker effectively reconstructs known input maps from simulated data.

The method provides insights into directional noise dependence and sky sensitivity.

Abstract

Given the recent advances in gravitational-wave detection technologies, the detection and characterisation of gravitational-wave backgrounds (GWBs) with the Laser Interferometer Space Antenna (LISA) is a real possibility. To assess the abilities of the LISA satellite network to reconstruct anisotropies of different angular scales and in different directions on the sky, we develop a map-maker based on an optimal quadratic estimator. The resulting maps are maximum likelihood representations of the GWB intensity on the sky integrated over a broad range of frequencies. We test the algorithm by reconstructing known input maps with different input distributions and over different frequency ranges. We find that, in an optimal scenario of well understood noise and high frequency, high SNR signals, the maximum scales LISA may probe are $\ell_{\rm max} \lesssim 15$. The map-maker also allows to test the directional dependence of LISA noise, providing insight on the directional sky sensitivity we may expect.