All-sky search for periodic gravitational waves in the full S5 LIGO data

Abstract

We report on an all-sky search for periodic gravitational waves in the frequency band 50--800 Hz and with the frequency time derivative in the range of 0 through $\ensuremath{-}6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}\text{ }\text{ }\mathrm{Hz}/\mathrm{s}$. Such a signal could be produced by a nearby spinning and slightly nonaxisymmetric isolated neutron star in our Galaxy. After recent improvements in the search program that yielded a $10\ifmmode\times\else\texttimes\fi{}$ increase in computational efficiency, we have searched in two years of data collected during LIGO's fifth science run and have obtained the most sensitive all-sky upper limits on gravitational-wave strain to date. Near 150 Hz our upper limit on worst-case linearly polarized strain amplitude ${h}_{0}$ is $1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}24}$, while at the high end of our frequency range we achieve a worst-case upper limit of $3.8\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}24}$ for all polarizations and sky locations. These results constitute a factor of 2 improvement upon previously published data. A new detection pipeline utilizing a loosely coherent algorithm was able to follow up weaker outliers, increasing the volume of space where signals can be detected by a factor of 10, but has not revealed any gravitational-wave signals. The pipeline has been tested for robustness with respect to deviations from the model of an isolated neutron star, such as caused by a low-mass or long-period binary companion.