Mapping Incoherent Gravitational Wave Backgrounds

TL;DR

This paper develops and tests a maximum-likelihood map-making algorithm to reconstruct sky maps of incoherent gravitational wave backgrounds, aiding astrophysical and cosmological investigations as detector sensitivity improves.

Contribution

It introduces a pixel-based maximum-likelihood method for creating sky maps of gravitational wave backgrounds using cross-correlation data, and demonstrates its effectiveness with simulated and real data.

Findings

Successfully reconstructs known input maps from simulated data.

Produces initial gravitational wave background maps from LIGO data.

Validates the map-making approach for future gravitational wave observations.

Abstract

Given the recent detection of gravitational waves from individual sources it is almost a certainty that some form of background of gravitational waves will be detected in future. The most promising candidate for such a detection are backgrounds made up of incoherent superposition of the signal of unresolved astrophysical or, backgrounds sourced by earlier cosmological events. Such backgrounds will also contain anisotropies about an average value. The information contained in the background level and any anisotropies will be extremely valuable as an astrophysical and cosmological probe. As such, the ability to reconstruct sky maps of the signal will become important as the sensitivity increases. We build and test a pixel--based, maximum--likelihood Gravitational Wave Background (GWB) map-maker that uses the cross-correlation of sets of generalised baselines as input. The resulting maps are a representation of the GWB power, or strain "intensity" on the sky. We test the algorithm by reconstructing known input maps with different baseline configurations. We also apply the map-maker to a subset of the Advance LIGO data.