Gravitational Wave Background Sky Maps from Advanced LIGO O1 Data
We integrate the publicly available O1 LIGO time-domain data to obtain maximum-likelihood constraints on the Gravitational Wave Background (GWB) arising from stochastic, persistent signals. Our method produces sky-maps of the strain intensity $I$ as a function of direction on the sky at a reference frequency $f_0$. The data is integrated assuming a set of fixed power-law spectra for the signal. The maps provide upper limits on the amplitude of the GWB density $\Omega_{\rm GW}(f_0)$ and any anisotropy around the background. We find 95\% confidence upper limits of $\Omega_{\rm GW} < 4.8\times 10^{-7}$ at $f_0=50$ Hz with similar constraints on a dipole modulation for the inspiral-dominated stochastic background case.