Identification and removal of non-Gaussian noise transients for gravitational wave searches

We present a new ${\it{gating}}$ method to remove non-Gaussian noise transients in gravitational wave data. The method does not rely on any a-priori knowledge on the amplitude or duration of the transient events. In light of the character of the newly released LIGO O3a data, glitch-identification is particularly relevant for searches using this data. Our method preserves more data than previously achieved, while obtaining the same, if not higher, noise reduction. We achieve a $\approx$ 2-fold reduction in zeroed-out data with respect to the gates released by LIGO on the O3a data. We describe the method and characterise its performance. While developed in the context of searches for continuous signals, this method can be used to prepare gravitational wave data for any search. As the cadence of compact binary inspiral detections increases and the lower noise level of the instruments unveils new glitches, excising disturbances effectively, precisely, and in a timely manner, becomes more important. Our method does this. We release the source code associated with this new technique and the gates for the newly released O3 data

Density-clustering of continuous gravitational wave candidates from large surveys

Searches for continuous gravitational waves target nearly monochromaticgravitational wave emission from e.g. non-axysmmetric fast-spinning neutronstars. Broad surveys often require to explicitly search for a very large numberof different waveforms, easily exceeding $\sim10^{17}$ templates. In suchcases, for practical reasons, only the top, say $\sim10^{10}$, results aresaved and followed-up through a hierarchy of stages. Most of these candidatesare not completely independent of neighbouring ones, but arise due to somecommon cause: a fluctuation, a signal or a disturbance. By judiciouslyclustering together candidates stemming from the same root cause, thesubsequent follow-ups become more effective. A number of clustering algorithmshave been employed in past searches based on iteratively finding symmetric andcompact over-densities around candidates with high detection statistic values.The new clustering method presented in this paper is a significant improvementover previous methods: it is agnostic about the shape of the over-densities, isvery efficient and it is effective: at a very high detection efficiency, it hasa noise rejection of $99.99\%$ , is capable of clustering two orders ofmagnitude more candidates than attainable before and, at fixed sensitivity itenables more than a factor of 30 faster follow-ups. We also demonstrate how tooptimally choose the clustering parameters.<br

Deep Einstein@Home all-sky search for continuous gravitational waves in LIGO O3 public data

We present the results of an all-sky search for continuous gravitational waves in the public LIGO O3 data. The search covers signal frequencies $20$ Hz $\leq f \leq 800$ Hz and a spin-down range down to $-2.6\times 10^{-9}$ Hz s$^{-1}$1, motivated by detectability studies on synthetic populations of Galactic neutron stars. This search is the most sensitive all-sky search to date in this frequency/spin-down region. The initial search was performed using the first half of the public LIGO O3 data (O3a), utilizing Graphical Processing Units provided in equal parts by the volunteers of the Einstein@Home computing project and by the ATLAS cluster. After a hierarchical follow-up in seven stages, 12 candidates remain. Six are discarded at the eighth stage, by using the remaining O3 LIGO data (O3b). The surviving six can be ascribed to continuous-wave fake signals present in the LIGO data for validation purposes. We recover these fake signals with very high accuracy with our last stage search, which coherently combines all O3 data. Based on our results, we set upper limits on the gravitational wave amplitude $h_0$, and translate these in upper limits on the neutron star ellipticity and on the $r$-mode amplitude. The most stringent upper limits are at $203$ Hz, with $h_0=8.1 \times 10^{-26}$ at the 90% confidence level. Our results exclude neutron stars rotating faster than $5$ ms with ellipticities greater than $5\times 10^{-8} \left[{d\over{100~\textrm{pc}}}\right]$ within a distance $d$ from Earth and $r$-mode amplitudes $\alpha \geq 10^{-5} \left[{d\over{100~\textrm{pc}}}\right]$ for neutron stars spinning faster than $150$ Hz.Comment: Accepted for publication in The Astrophysical Journal on 31 May 2023. 13 pages, 10 figures, 3 table

Results from an Einstein@Home search for continuous gravitational waves from G347.3 at low frequencies in LIGO O2 data

We present results of a search for periodic gravitational wave signals with frequency between 20 and 400 Hz, from the neutron star in the supernova remnant G347.3-0.5, using LIGO O2 public data. The search is deployed on the volunteer computing project Einstein@Home, with thousands of participants donating compute cycles to make this endevour possible. We find no significant signal candidate and set the most constraining upper limits to date on the amplitude of gravitational wave signals from the target, corresponding to deformations below $10^{-6}$ in a large part of the band. At the frequency of best strain sensitivity, near $166$ Hz, we set 90\%\ confidence upper limits on the gravitational wave intrinsic amplitude of $h_0^{90\%}\approx 7.0\times10^{-26}$. Over most of the frequency range our upper limits are a factor of 20 smaller than the indirect age-based upper limit

Deep Einstein@Home All-sky Search for Continuous Gravitational Waves in LIGO O3 Public Data

We present the results of an all-sky search for continuous gravitational waves in the public LIGO O3 data. The search covers signal frequencies 20.0 Hz ≤ f ≤ 800.0 Hz and a spin-down range down to −2.6 × 10−9 Hz s−1, motivated by detectability studies on synthetic populations of Galactic neutron stars. This search is the most sensitive all-sky search to date in this frequency/spin-down region. The initial search was performed using the first half of the public LIGO O3 data (O3a), utilizing graphical processing units provided in equal parts by the volunteers of the Einstein@Home computing project and by the ATLAS cluster. After a hierarchical follow-up in seven stages, 12 candidates remain. Six are discarded at the eighth stage, by using the remaining O3 LIGO data (O3b). The surviving six can be ascribed to continuous-wave fake signals present in the LIGO data for validation purposes. We recover these fake signals with very high accuracy with our last stage search, which coherently combines all O3 data. Based on our results, we set upper limits on the gravitational-wave amplitude h 0 and translate these into upper limits on the neutron star ellipticity and on the r-mode amplitude. The most stringent upper limits are at 203 Hz, with h 0 = 8.1 × 10−26 at the 90% confidence level. Our results exclude isolated neutron stars rotating faster than 5 ms with ellipticities greater than 5 × 10 − 8 d 100 pc within a distance d from Earth and r-mode amplitudes α ≥ 10 − 5 d 100 pc for neutron stars spinning faster than 150 Hz

Results from an Einstein@Home Search for Continuous Gravitational Waves from G347.3 at Low Frequencies in LIGO O2 Data

We present results of a search for periodic gravitational wave signals with frequencies between 20 and 400 Hz from the neutron star in the supernova remnant G347.3-0.5 using LIGO O2 public data. The search is deployed on the volunteer computing project Einstein@Home, with thousands of participants donating compute cycles to make this endeavour possible. We find no significant signal candidate and set the most constraining upper limits to date on the amplitude of gravitational wave signals from the target, corresponding to deformations below 10-6 in a large part of the band. At the frequency of best strain sensitivity, near 166 Hz, we set 90% confidence upper limits on the gravitational wave intrinsic amplitude of . Over most of the frequency range our upper limits are a factor of 20 smaller than the indirect age-based upper limit. © 2022. The Author(s). Published by the American Astronomical Society.

Results of an all-sky high-frequency Einstein@Home search for continuous gravitational waves in LIGO's fifth science run

We present results of a high-frequency all-sky search for continuous gravitational waves from isolated compact objects in LIGO's fifth science run (S5) data, using the computing power of the Einstein@Home volunteer computing project. This is the only dedicated continuous gravitational wave search that probes this high-frequency range on S5 data. We find no significant candidate signal, so we set 90% confidence level upper limits on continuous gravitational wave strain amplitudes. At the lower end of the search frequency range, around 1250 Hz, the most constraining upper limit is 5.0×10-24, while at the higher end, around 1500 Hz, it is 6.2×10-24. Based on these upper limits, and assuming a fiducial value of the principal moment of inertia of 1038 kg m2, we can exclude objects with ellipticities higher than roughly 2.8×10-7 within 100 pc of Earth with rotation periods between 1.3 and 1.6 milliseconds

Einstein@Home all-sky search for continuous gravitational waves in LIGO O2 public data

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 between 20.0 Hz and 585.15 Hz and spin-down between -2.6e-9 Hz/s and 2.6e-10 Hz/s. 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 h0 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 h0 = 1.3e25, at the 90% confidence level. Our results exclude neutron stars rotating faster than 5 ms with equatorial ellipticities larger than 1e-7 closer than 100 pc. These are deformations that neutron star crusts could easily support, according to some models

Einstein@Home discovery of four young gamma-ray pulsars in Fermi LAT data

We report the discovery of four gamma-ray pulsars, detected in computing-intensive blind searches of data from the Fermi Large Area Telescope (LAT). The pulsars were found using a novel search approach, combining volunteer distributed computing via Einstein@Home and methods originally developed in gravitational-wave astronomy. The pulsars PSRs J0554+3107, J1422-6138, J1522-5735, and J1932+1916 are young and energetic, with characteristic ages between 35 and 56 kyr and spin-down powers in the range $6\times10^{34}$ - $10^{36}$ erg s$^{-1}$. They are located in the Galactic plane and have rotation rates of less than 10 Hz, among which the 2.1 Hz spin frequency of PSR J0554+3107 is the slowest of any known gamma-ray pulsar. For two of the new pulsars, we find supernova remnants coincident on the sky and discuss the plausibility of such associations. Deep radio follow-up observations found no pulsations, suggesting that all four pulsars are radio-quiet as viewed from Earth. These discoveries, the first gamma-ray pulsars found by volunteer computing, motivate continued blind pulsar searches of the many other unidentified LAT gamma-ray sources