First low-frequency Einstein@Home all-sky search for continuous gravitational waves in Advanced LIGO data

Abstract

We report results of a deep all-sky search for periodic gravitational waves from isolated neutron stars in data from the first Advanced LIGO observing run. This search investigates the low frequency range of Advanced LIGO data, between 20 and 100 Hz, much of which was not explored in initial LIGO. The search was made possible by the computing power provided by the volunteers of the Einstein@Home project. We find no significant signal candidate and set the most stringent upper limits to date on the amplitude of gravitational wave signals from the target population, corresponding to a sensitivity depth of 48.7 ½1= ffiffiffiffiffiffi Hz p . At the frequency of best strain sensitivity, near 100 Hz, we set 90% confidence upper limits of 1.8 × 10 −25 . At the low end of our frequency range, 20 Hz, we achieve upper limits of 3.9 × 10 −24 . At 55 Hz we can exclude sources with ellipticities greater than 10 −5 within 100 pc of Earth with fiducial value of the principal moment of inertia of 10 38 kg m 2 .

All-sky search for periodic gravitational waves in the O1 LIGO data

“…Manual follow-up has shown noninjection outliers spanning all three segments to be caused by pronounced detector artifacts. Several outliers (numbers 47, 56, 70, 72, 134, 138, 154 in Table VIII) spanning two segments were also investigated with a fully coherent followup based on the Einstein@Home pipeline [31,32]. None was found to be consistent with the astrophysical signal model.…”

“…Converting the PowerFlux upper limits to validated population-averaged upper limits would require extensive, band-dependent Monte Carlo simulations, but previous studies suggest that such limits would lie in a region similar to that of the other pipelines. In addition, the population-averaged upper limits from the most recent Einstein@Home search are shown for comparison [32]. The Einstein@Home search explored the low frequencies, and a narrower spin-down range using a much longer coherence length (210 hours).…”

“…Any outliers that survive all stages of any of the four pipelines are examined manually for contamination from known instrumental artifacts and for evidence of contamination from a previously unknown single-interferometer artifact. Those for which no artifacts are found are subjected to the additional systematic followup used for Einstein@Home searches [31,32], which includes a final stage with full coherence across the entire data run.…”

“…The deep follow-up used the same method [31,32] as for persistent outliers in the other search pipelines. Again, no credible signals were found.…”

“…23 the outlier joint Hough map. For these outliers we have carried out a deeper follow-up using the method described in [31,32], with a coherence time of 210 hours. In all cases the follow-up failed to yield a credible signal.…”