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Einstein@Home’s most sensitive continuous gravitational-wave search

Max Planck scientists used a distributed volunteer computing project and three supercomputers to conduct the deepest all-sky search yet for elusive continuous gravitational waves.

The Galactic population of neutron stars is a promising source of continuous gravitational waves, which have yet to be detected. Since the sky positions, spin frequencies, and frequency derivatives of individual sources are unknown, wide-band, all-sky searches are one of the main tools used in the field. Researchers from the independent Max Planck research group “Continuous Gravitational Waves” at the AEI Hannover have published the deepest all-sky search for continuous gravitational waves to date. Using the distributed volunteer computing project Einstein@Home and the Max Planck Society’s computing clusters Atlas, Raven, and Viper, they analyzed public data from LIGO’s third observing run (O3). All hardware injections — signals “added” artificially to the data by moving the LIGO mirrors — within the search range were recovered. Additionally, this is the first search to successfully detect hardware injection 11. No astrophysical signals were observed. In the most sensitive frequency band, the upper limits on continuous gravitational-wave strain improved by approximately 70% compared to the most sensitive LIGO-Virgo-KAGRA analyses of O3 data. The team expects their O3 results to be competitive with LIGO-Virgo-KAGRA analyses based on fourth observing run (O4) data, which is not yet publicly available.

Paper abstract

We present results from the most sensitive all-sky search to date for continuous gravitational waves with frequencies 30.0 Hz ≤ f ≤ 250.0 Hz and frequency derivatives -2.7×10^-9 Hz s^-1 ≤ ḟ ≤ 0.2×10^-9 Hz s^-1. We deploy this search on the Einstein@Home volunteer-computing project and on three supercomputer clusters. At the end of a multistage approach there are four surviving candidates: three from “hardware injections,” i.e., signals “added” by moving the instruments’ mirrors, and one due to line disturbances in the data. The high sensitivity of our search enabled the first-ever detection of hardware injection 11. We set upper limits on the gravitational wave amplitude h₀, and translate these to upper limits on the neutron star ellipticity and on the r-mode amplitude. The most stringent upper limits are at 173 Hz with h₀ = 6.5×10^-26, at the 90% confidence level, which improve by about 70% with respect to the LIGO-Virgo-KAGRA Collaboration’s most stringent O3 upper limits, and might well be competitive with results from O4 searches.