Upper limit map of a background of gravitational waves

We searched for an anisotropic background of gravitational waves usingdata from the LIGO S4 science run and a method that is optimizedfor point sources. This is appropriate if, for example, the gravitationalwave background is dominated by a small number of distinct astrophysical sources.No signal was seen. Upper limit maps were produced assuming two differentpower laws for the source strain power spectrum. For an f^-3 power law and using the50 Hz to 1.8 kHz band the upper limits on the sourcestrain power spectrum vary between 1.2×10^-48 Hz^-1 (100 Hz/f)³ and 1.2×10^-47 Hz^-1 (100 Hz/f)³, depending on the position in the sky. Similarly,in the case of constant strain power spectrum, the upper limits vary between 8.5×10^-49 Hz^-1 and 6.1×10^-48 Hz^-1. As a side product a limiton an isotropic background of gravitational waves was also obtained. All limitsare at the 90% confidence level. Finally, as an application, we focused onthe direction of Sco-X1, the brightest low-mass x-ray binary. We compare theupper limit on strain amplitude obtained by this method to expectations basedon the x-ray flux from Sco-X1.