High-frequency Continuous Gravitational Wave Search in LIGO O3 Public Data with Einstein@Home

We search for nearly monochromatic gravitational-wave signals with frequencies 800.0 Hz ≤ f ≤ 1686.0 Hz and spin-down − 2.7 × 1 0 − 9 Hz s − 1 ≤ f ̇ ≤ 0.2 × 1 0 − 9 Hz s − 1 . We use LIGO O3 public data from the Hanford and Livingston detectors, and deploy this search on the Einstein@Home volunteer-computing project. This is the most sensitive search carried out to date in this parameter space. Our results are consistent with a nondetection. We set upper limits on the gravitational-wave amplitude h 0 and translate these to upper limits on neutron star ellipticity and on r -mode amplitude. The most stringent upper limits are at 800 Hz, with h 0 = 1.32 × 10 −25 at the 90% confidence level. Searching in the high-frequency bands allows us to probe astrophysically interesting ellipticities with our results, excluding isolated neutron stars rotating faster than 2.5 ms with ellipticities ϵ ≥ 1.96 × 1 0 − 8 d 100 pc within a distance d from Earth. Our results also exclude r -mode amplitudes α ≥ 7 × 1 0 − 7 d 100 pc for neutron stars spinning faster than 400 Hz.