Superradiance can trigger the formation of an ultralight boson cloud around a spinning black hole. Once formed, the boson cloud is expected to emit a nearly periodic, long-duration, ...gravitational-wave signal. For boson masses in the range (10−13–10−11) eV, and stellar mass black holes, such signals are potentially detectable by gravitational-wave detectors, like Advanced LIGO and Virgo. In this Letter, we present full band upper limits for a generic all-sky search for periodic gravitational waves in LIGO O2 data, and use them to derive-for the first time-direct constraints on the ultralight scalar boson field mass.
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While gravitational waves have been detected from mergers of binary black holes and binary neutron stars, signals from core collapse supernovae, the most energetic explosions in the modern Universe, ...have not been detected yet. Here we present a new method to analyse the data of the LIGO, Virgo, and KAGRA network to enhance the detection efficiency of this category of signals. The method takes advantage of a peculiarity of the gravitational wave signal emitted in the core collapse supernova and it is based on a classification procedure of the time-frequency images of the network data performed by a convolutional neural network trained to perform the task to recognize the signal. We validate the method using phenomenological waveforms injected in Gaussian noise whose spectral properties are those of the LIGO and Virgo advanced detectors and we conclude that this method can identify the signal better than the present algorithm devoted to select gravitational wave transient signal.
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As a consequence of superradiant instability induced in Kerr black holes, ultralight boson clouds can be a source of persistent gravitational waves, potentially detectable by current and future ...gravitational-wave detectors. These signals have been predicted to be nearly monochromatic, with a small steady frequency increase (spin-up), but given the several assumptions and simplifications done at theoretical level, it is wise to consider, from the data analysis point of view, a broader class of gravitational signals in which the phase (or the frequency) slightly wander in time. Also other types of sources, e.g., neutron stars in which a torque balance equilibrium exists between matter accretion and emission of persistent gravitational waves, would fit in this category. In this paper we present a robust and computationally cheap analysis pipeline devoted to the search of such kind of signals. We provide a full characterization of the method, through both a theoretical sensitivity estimation and through the analysis of synthetic data in which simulated signals have been injected. The search setup for both all-sky searches and higher sensitivity directed searches is discussed.
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In this work we present the results of a search for continuous gravitational waves from the Galactic Center using LIGO O2 data. The search uses the band-sampled-data directed search pipeline, which ...performs a semicoherent wide-parameter-space search, exploiting the robustness of the FrequencyHough transform algorithm. The search targets signals emitted by isolated asymmetric spinning neutron stars, located within 25–150 parsecs from the Galactic Center. The frequencies covered in this search range between 10 and 710 Hz with a spin-down range from −1.8×10−9 to 3.7×10−11 Hz/s. No continuous wave signal has been detected and upper limits on the gravitational wave amplitude are presented. The most stringent upper limit at 95% confidence level, for the Livingston detector, is ∼1.4×10−25 at frequencies near 160 Hz. To date, this is the most sensitive directed search for continuous gravitational-wave signals from the Galactic Center and the first search of this kind using the LIGO second observing run.
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Continuous gravitational wave signals, like those expected by asymmetric spinning neutron stars, are among the most promising targets for LIGO and Virgo detectors. The development of fast and robust ...data analysis methods is crucial to increase the chances of a detection. We have developed a new and flexible general data analysis framework for the search of this kind of signals, which allows to reduce the computational cost of the analysis by about two orders of magnitude with respect to current procedures. This can correspond, at fixed computing cost, to a sensitivity gain of up to 10%-20%, depending on the search parameter space. Some possible applications are discussed, with a particular focus on a directed search for sources in the Galactic center. Validation through the injection of artificial signals in the data of Advanced LIGO first observational science run is also shown.
Rapidly rotating neutron stars are promising sources of continuous gravitational wave radiation for the LIGO and Virgo interferometers. The majority of neutron stars in our galaxy have not been ...identified with electromagnetic observations. All-sky searches for isolated neutron stars offer the potential to detect gravitational waves from these unidentified sources. The parameter space of these blind all-sky searches, which also cover a large range of frequencies and frequency derivatives, presents a significant computational challenge. Different methods have been designed to perform these searches within acceptable computational limits. Here we describe the first benchmark in a project to compare the search methods currently available for the detection of unknown isolated neutron stars. The five methods compared here are individually referred to as the PowerFlux, sky Hough, frequency Hough, Einstein@Home, and time domain F-statistic methods. We employ a mock data challenge to compare the ability of each search method to recover signals simulated assuming a standard signal model. We find similar performance among the four quick-look search methods, while the more computationally intensive search method, Einstein@Home, achieves up to a factor of two higher sensitivity. We find that the absence of a second derivative frequency in the search parameter space does not degrade search sensitivity for signals with physically plausible second derivative frequencies. We also report on the parameter estimation accuracy of each search method, and the stability of the sensitivity in frequency and frequency derivative and in the presence of detector noise.
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The 'First Generation Era' of gravitational wave detectors is now over, but the data analysis effort for the search of continuous gravitational waves is still ongoing and active. Many results have ...been produced but still many searches are underway. I present and discuss here the most recent results for this search, together with short discussions on analysis which are now underway and plans for the near future. The discussion on long-term plans and perspectives for the so-called Advanced Detector Era are beyond the scope of this paper.
A method for searching continuous gravitational wave signals from isolated neutron stars whose position, frequency and frequency evolution are known is described in this paper. This method is applied ...to data of interferometric detectors such as Virgo. The method is based on the use of 5-vectors, which are the Fourier components of the signal and data at five frequencies around the source intrinsic frequency. The main characteristics of the method are its simplicity and the strong reduction of the computing time needed for the analysis and in particular for all the simulation procedures. We also introduce here the concept of 'coherence' to state the reliability of a detection.
Continuous gravitational waves signals, emitted by asymmetric spinning neutron stars, are among the main targets of current detectors like Advanced LIGO and Virgo. In the case of sources, like ...pulsars, whose rotational parameters are measured through electromagnetic observations, typical searches assume that the gravitational wave frequency is at a given known fixed ratio with respect to the star rotational frequency. For instance, for a neutron star rotating around one of its principal axis of inertia the gravitational signal frequency would be exactly two times the rotational frequency of the star. It is possible, however, that this assumption is wrong. This is why search algorithms able to take into account a possible small mismatch between the gravitational waves frequency and the frequency inferred from electromagnetic observations have been developed. In this paper we present an improved pipeline to perform such narrow-band searches for continuous gravitational waves from neutron stars, about three orders of magnitude faster than previous implementations. The algorithm that we have developed is based on the 5-vectors framework and is able to perform a fully coherent search over a frequency band of width O(Hertz) and for hundreds of spin-down values running a few hours on a standard workstation. This new algorithm opens the possibility of long coherence time searches for objects whose rotational parameters are highly uncertain as shown in the case study of the central compact object in the supernova remnant G353.6-0.7.
In this paper we introduce a novel filtering method for the search of continuous gravitational wave signals in the data of interferometric detectors, based on the estimation of the harmonic content ...of the detector sidereal pattern. Thanks to the very specific properties of the sidereal modulation, the method is powerful in discriminating among continuous wave signals of astrophysical origin and detector artefacts or noise outliers. We describe here the statistical properties of the filter by using both software and hardware simulated signals injected in the data of the LIGO second science run O2 and we give an estimate of the method sensitivity. A study of the method robustness with respect to a nonoptimal correction of the signal frequency variation, referring in particular to the spin-down, is also presented. This novel filtering procedure is well suited for directed searches of sources with known-or loosely known-position and largely unknown frequency and spin-down, and for the follow-up of all-sky candidates. Used as an initial processing step it has, moreover, the potential to improve the sensitivity of wide-band hierarchical searches.
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