Abstract
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 20.0 Hz ≤ f ≤ 585.15 Hz and spin-down Hz s−1. 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 h 0 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 h 0 = 1.3 × 10−25, at the 90% confidence level. Our results exclude neutron stars rotating faster than 5 ms with equatorial ellipticities larger than 10−7 closer than 100 pc. These are deformations that neutron star crusts could easily support, according to some models.
Highlights
We search for nearly-monochromatic signals with frequency 20.0 Hz ≤ f ≤ 585.15 Hz and spin-down −2.6 × 10−9 Hz/s ≤ f ≤ 2.6 × 10−10 Hz/s
We find no evidence of a continuous gravitational wave signal at the detectability level of our search
In this paper we present the results from an all-sky search for continuous gravitational wave signals with frequency f between 20.0 Hz and 585.15 Hz and spin-down −2.6 × 10−9 Hz/s ≤ f ≤ 2.6 × 10−10 Hz/s, carried out thanks to the computing power donated by the volunteers of the Einstein@Home project
Summary
Continuous gravitational waves are expected in a variety of astrophysical scenarios: from rotating neutrons stars if they present some sort of asymmetry with respect to their rotation axis or through the excitation of unstable r-modes (Lasky 2015; Owen et al 1998); from the fast inspiral of dark-matter objects (Horowitz & Reddy 2019; Horowitz et al 2020); through superradiant emission of axion-like particles around black holes (Arvanitaki et al 2015; Zhu et al 2020). We use LIGO O2 public data (Abbott et al 2019b; Vallisneri et al 2015; LIGO 2019) and, thanks to a much longer coherent-search baseline, achieve a significantly higher sensitivity than the LIGO Collaboration O2 results in the same frequency range (Abbott et al 2019a; Palomba et al 2019). Our results complement those of the high-frequency Falcon search (Dergachev & Papa 2020), which cover the range from 500 to 1700 Hz. The plan of the paper is the following: we introduce the signal model and generalities about the search in Sections 2 and 3, respectively.
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