We report on an all-sky search for periodic gravitational waves in the frequency range $mathrm{50-1000 Hz}$ with the first derivative of frequency in the range $-8.9 times 10^{-10}$ Hz/s to zero in two years of data collected during LIGOs fifth scien
ce run. Our results employ a Hough transform technique, introducing a $chi^2$ test and analysis of coincidences between the signal levels in years 1 and 2 of observations that offers a significant improvement in the product of strain sensitivity with compute cycles per data sample compared to previously published searches. Since our search yields no surviving candidates, we present results taking the form of frequency dependent, 95$%$ confidence upper limits on the strain amplitude $h_0$. The most stringent upper limit from year 1 is $1.0times 10^{-24}$ in the $mathrm{158.00-158.25 Hz}$ band. In year 2, the most stringent upper limit is $mathrm{8.9times10^{-25}}$ in the $mathrm{146.50-146.75 Hz}$ band. This improved detection pipeline, which is computationally efficient by at least two orders of magnitude better than our flagship Einstein$@$Home search, will be important for quick-look searches in the Advanced LIGO and Virgo detector era.
$chi^2$ vetoes are commonly used in searching for gravitational waves, in particular for broad-band signals, but they can also be applied to narrow-band continuous wave signals, such as those expected from rapidly rotating neutron stars. In this pape
r we present a $chi^2$ veto adapted to the Hough transform searches for continuous gravitational wave signals; we characterize the $chi^2$-significance plane for different frequency bands; and discuss the expected performance of this veto in LIGO analysis.
We study parameter estimation of supermassive black holes in the range $10^5-10^8Ms$ by LISA using the inspiral full post-Newtonian gravitational waveforms, and we compare the results with those arising from the commonly used restricted post-Newtonia
n approximation. The analysis shows that for observations of the last year before merger, the inclusion of the higher harmonics clearly improves the parameter estimation. We pay special attention to the source location errors and we study the improvement on the percentage of sources for which we could potentially identify electromagnetic counterparts. We also show how the additional harmonics can help to mitigate the impact of losing laser links during the mission.
We study parameter estimation of supermassive black hole binary systems in the final stage of inspiral using the full post-Newtonian gravitational waveforms. We restrict our analysis to systems in circular orbit with negligible spins, in the mass ran
ge $10^8Ms-10^5Ms$, and compare the results with those arising from the commonly used restricted post-Newtonian approximation. The conclusions of this work are particularly important with regard to the astrophysical reach of future LISA measurements. Our analysis clearly shows that modeling the inspiral with the full post-Newtonian waveform, not only extends the reach to higher mass systems, but also improves in general the parameter estimation. In particular, there are remarkable improvements in angular resolution and distance measurement for systems with a total mass higher than $5times10^6Ms$, as well as a large improvement in the mass determination.
