Abstract
This paper presents results of an all-sky searches for periodic gravitational waves in the frequency range [50, 1190] Hz and with frequency derivative ranges of [-2 x 10^-9, 1.1 x 10^-10] Hz/s for the fifth LIGO science run (S5). The novelty of the search lies in the use of a non-coherent technique based on the Hough-transform to combine the information from coherent searches on timescales of about one day. Because these searches are very computationally intensive, they have been deployed on the Einstein@Home distributed computing project infrastructure. The search presented here is about a factor 3 more sensitive than the previous Einstein@Home search in early S5 LIGO data. The post-processing has left us with eight surviving candidates. We show that deeper follow-up studies rule each of them out. Hence, since no statistically significant gravitational wave signals have been detected, we report upper limits on the intrinsic gravitational wave amplitude h0. For example, in the 0.5 Hz-wide band at 152.5 Hz, we can exclude the presence of signals with h0 greater than 7.6 x 10^-25 with a 90% confidence level.
Highlights
A promising class of sources for detectable gravitational wave signals is rapidly rotating neutron stars with nonaxisymmetric deformations [1,2,3,4,5]
This search is about a factor 3 more sensitive than the previous Einstein@Home search of early S5 LIGO data
We proceed to set upper limits on the maximum intrinsic gravitational wave strain h0 that is consistent with our observations for a population of CW signals described by Eq (8), from random positions in the sky, in the gravitational wave frequency range 1⁄250:5; 1 190 Hz, and with spin-down values in the range of $1⁄2À20; 1:1 Â 10À10 Hz sÀ1
Summary
A promising class of sources for detectable gravitational wave signals is rapidly rotating neutron stars with nonaxisymmetric deformations [1,2,3,4,5]. The amplitude sensitivity grows at best with the fourth root of the number of segments Such methods have been used in previous wide-parameter-space searches published by the LIGO and Virgo Collaborations [21,22,23,24,25,26]. The method used was based on the computation of the coherent F -statistic on data segments from either the H or L detectors separately, and only parameter space points with values of 2F larger than 25 were returned back to the Einstein@Home server for further inspection. This makes it possible to use a much lower threshold on 2F , equal to 5.2, that defines the parameter space points to be passed on to the Hough transform In this search, data from the H and L detectors are coherently combined [13,14].
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