Directional limits on persistent gravitational waves using LIGO S5 science data

TL;DR

This paper presents the first directional searches for persistent gravitational waves using LIGO S5 data, setting new upper limits on GW strain power for pointlike and extended sources across the sky.

Contribution

It introduces a novel extended-source search method and provides the first upper limits for such sources, improving constraints on GW signals from various astrophysical objects.

Findings

No GW signals detected; upper limits set.

Pointlike source limits improved by a factor of 30.

Extended source limits established for the first time.

Abstract

The gravitational-wave (GW) sky may include nearby pointlike sources as well as astrophysical and cosmological stochastic backgrounds. Since the relative strength and angular distribution of the many possible sources of GWs are not well constrained, searches for GW signals must be performed in a model-independent way. To that end we perform two directional searches for persistent GWs using data from the LIGO S5 science run: one optimized for pointlike sources and one for arbitrary extended sources. The latter result is the first of its kind. Finding no evidence to support the detection of GWs, we present 90% confidence level (CL) upper-limit maps of GW strain power with typical values between 2-20x10^-50 strain^2 Hz^-1 and 5-35x10^-49 strain^2 Hz^-1 sr^-1 for pointlike and extended sources respectively. The limits on pointlike sources constitute a factor of 30 improvement over the previous best limits. We also set 90% CL limits on the narrow-band root-mean-square GW strain from interesting targets including Sco X-1, SN1987A and the Galactic Center as low as ~7x10^-25 in the most sensitive frequency range near 160 Hz. These limits are the most constraining to date and constitute a factor of 5 improvement over the previous best limits.