Abstract
We present the first atlas of the continuous gravitational wave sky, produced using LIGO O3a public data. For each 0.045 Hz frequency band and every point on the sky the atlas provides gravitational wave amplitude upper limits, signal-to-noise ratios (SNRs), and frequencies where the search measures the maximum SNR. The approximately top 1.5% of the atlas results are reanalyzed with a series of more sensitive searches with the purpose of finding high SNR long coherence signals from isolated neutron stars. However, these searches do not reveal the presence of such signals. The results presented in the atlas are produced with the Falcon pipeline and cover nearly monochromatic gravitational-wave signals in the 500–1000 Hz band, with up to frequency derivative. The Falcon pipeline computes loosely coherent power estimates to search data using a succession of coherence lengths. For this search we use six months of data, started with a 12 hour coherence length and progress to six days. Compared to the most sensitive results previously published (also produced with the Falcon pipeline), our upper limits are 50% more constraining. Neutron stars with ellipticity of can be detected up to 150 pc away, while allowing for a large fraction of the stars’ energy to be lost through nongravitational channels. These results are within an order of magnitude of the minimum neutron star ellipticity of suggested by Woan et al. [Astrophys. J. Lett. 863, L40 (2018)
- Received 21 February 2022
- Revised 10 March 2023
- Accepted 10 April 2023
DOI:https://doi.org/10.1103/PhysRevX.13.021020
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Open access publication funded by the Max Planck Society.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
To date, all detected gravitational waves have come in bursts from transient events such as black hole and neutron star mergers. In contrast, continuous gravitational waves (CGWs) are expected from nonaxisymmetric neutron stars. These signals are orders of magnitude weaker and much harder to identify than their short-lived counterparts. In fact, there are no confirmed associations between CGW outliers in gravitational-wave data and astrophysical objects. However, once discovered, sources of CGWs allow for repeated observations and can also be studied via simultaneous observations of gravitational-wave and electromagnetic-wave emission. In this paper, we provide a measure of the CGW amplitude for every location in the sky as well as an indicator of the likelihood of there being a detectable signal from each location. Combined into an “atlas,” these results will enable new and independent searches for CGW sources.
The most promising sources of CGWs are rapidly rotating neutron stars, which must be deformed to produce a signal. Such stars emit gravitational waves at a frequency related to the star’s spin. Not knowing these frequencies a priori, we search through data from the Laser Interferometer Gravitational-Wave Observatory for continuous signals at all possible frequencies. These data are so sensitive that they can detect stars with equatorial bumps of at distances up to nearly 500 light-years from Earth. For every position in the sky, our analysis provides an upper limit to the CGW amplitude at each frequency and a signal-to-noise ratio, making it possible to rule out potential candidates and conduct new searches.
Investigating a small fraction of the atlas with follow-up searches, we did not find convincing evidence of any astrophysical signals. This suggests that one should look for weaker signals in the rest of the atlas. In fact, 98.5% of the atlas has not been analyzed and is waiting to be explored. Our atlas could be used by any interested searcher for CGW sources to perform their own analysis on computers as small as a personal laptop.
