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Abstract

We conduct an all-sky search for continuous gravitational waves in the LIGO
O2 data from the Hanford and Livingston detectors. We search for
nearly-monochromatic signals with frequency between 20.0 Hz and 585.15 Hz and
spin-down between -2.6e-9 Hz/s and 2.6e-10 Hz/s. We deploy the search on the
Einstein@Home volunteer-computing project and follow-up the waveforms
associated with the most significant results with eight further search-stages,
reaching the best sensitivity ever achieved by an all-sky survey up to 500 Hz.
Six of the inspected waveforms pass all the stages but they are all associated
with hardware-injections, which are fake signals simulated at the LIGO detector
for validation purposes. We recover all these fake signals with consistent
parameters. No other waveform survives, so we find no evidence of a continuous
gravitational wave signal at the detectability level of our search. We
constrain the h0 amplitude of continuous gravitational waves at the detector as
a function of the signal frequency, in half-Hz bins. The most constraining
upper limit at 163.0 Hz is h0 = 1.3e25, at the 90% confidence level. Our
results exclude neutron stars rotating faster than 5 ms with equatorial
ellipticities larger than 1e-7 closer than 100 pc. These are deformations that
neutron star crusts could easily support, according to some models.