Max Planck Institute for Gravitational Physics (Albert Einstein Institute)
Visualising the continuous gravitational-wave sky
The first atlas of the entire sky in continuous gravitational waves
June 24, 2022
Continuous gravitational waves are emitted by rapidly rotating deformed neutron stars. Detecting them would allow to study their otherwise invisible population in our Galaxy. Researchers from the permanent independent research group “Continuous Gravitational Waves” at the Max Planck Institute for Gravitational Physics in Hannover have analysed public LIGO data from O3a, the first half the third observing run. They created the first atlas of the entire continuous gravitational wave sky. It contains for every point on the sky and in narrow frequency bands information on the search results. No continuous gravitational-wave signal was identified, but the new results place tighter constraints on the population of rapidly rotating neutron stars as emitters of continuous gravitational waves.
Paper 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 upper limits, signal-to-noise ratios (SNR) and frequencies where the search measures the maximum SNR. 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 ±5 × 10−11 Hz/s frequency derivative. 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 10−8 can be detected up to 150 pc away, while allowing for a large fraction of the stars’ energy to be lost through non-gravitational channels.
Summary of atlas data from the bins between 835-840 Hz. The top panels show the highest SNR (left) and upper limit values (right) across the frequency band, for each pixel of the sky map, using equatorial coordinates. The red lines denote the galactic plane. The blue diamond shows the location of the outlier that is discarded based on the analysis of O3a+b data. The blue band of smaller SNRs near the ecliptic equator is due to large correlations between waveforms of sources in that region. The blue regions in the upper limit plot are due to the lower-SNR values in the ecliptic plane, and also occur near the ecliptic poles that are favored by the antenna pattern of the detectors. The bottom panels show the same data as a function of frequency and with the maximum taken over the sky. We mark the frequency of the band where the outlier mentioned above was found, the location of the only known line from the O3 line list in that band, and the band where we the maximum SNR is achieved in the ecliptic pole region - a region strongly a ected by instrumental lines. The data and code used to produce this plot is available.
Summary of atlas data from the bins between 835-840 Hz. The top panels show the highest SNR (left) and upper limit values (right) across the frequency band, for each pixel of the sky map, using equatorial coordinates. The red lines denote the galactic plane. The blue diamond shows the location of the outlier that is discarded based on the analysis of O3a+b data. The blue band of smaller SNRs near the ecliptic equator is due to large correlations between waveforms of sources in that region. The blue regions in the upper limit plot are due to the lower-SNR values in the ecliptic plane, and also occur near the ecliptic poles that are favored by the antenna pattern of the detectors. The bottom panels show the same data as a function of frequency and with the maximum taken over the sky. We mark the frequency of the band where the outlier mentioned above was found, the location of the only known line from the O3 line list in that band, and the band where we the maximum SNR is achieved in the ecliptic pole region - a region strongly a ected by instrumental lines. The data and code used to produce this plot is available.
