A method to search for long duration gravitational wave transients from isolated neutron stars using the generalized FrequencyHough

We describe a method to detect gravitational waves lasting $O(hours-days)$ emitted by young, isolated neutron stars, such as those that could form after a supernova or a binary neutron star merger, using advanced LIGO/Virgo data. The method is based on a generalization of the FrequencyHough (FH), a pipeline that performs hierarchical searches for continuous gravitational waves by mapping points in the time/frequency plane of the detector to lines in the frequency/spindown plane of the source. We show that signals whose spindowns are related to their frequencies by a power law can be transformed to coordinates where the behavior of these signals is always linear, and can therefore be searched for by the FH. We estimate the sensitivity of our search across different braking indices, and describe the portion of the parameter space we could explore in a search using varying fast Fourier Transform (FFT) lengths.Comment: 15 figure

Directed search for continuous gravitational-wave signals from the Galactic Center in the Advanced LIGO second observing run

International audienceIn 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

Impact of signal clusters in wide-band searches for continuous gravitational waves

International audienceIn this paper we present a study of some relevant steps of the hierarchical frequency-Hough (FH) pipeline, used within the LIGO and Virgo Collaborations for wide-parameter space searches of continuous gravitational waves (CWs) emitted, for instance, by spinning neutron stars (NSs). Because of their weak expected amplitudes, CWs have not been still detected so far. These steps, namely the spectral estimation, the peakmap construction and the procedure to select candidates in the FH plane, are critical as they contribute to determine the final search sensitivity. Here, we are interested in investigating their behavior in the (presently quite) extreme case of signal clusters, due to many and strong CW sources, emitting gravitational waves (GWs) within a small (i.e., <1  Hz wide) frequency range. This could happen for some kinds of CW sources detectable by next generation detectors, like LISA, Einstein Telescope, and Cosmic Explorer. Moreover, this possibility has been recently raised even for current Earth-based detectors, in some scenarios of CW emission from ultralight boson clouds around stellar mass black holes (BHs). We quantitatively evaluate the robustness of the FH analysis procedure, designed to minimize the loss of single CW signals, under the unusual situation of signal clusters. Results depend mainly on how strong in amplitude and dense in frequency the signals are, and on the range of frequency they cover. We show that indeed a small sensitivity loss may happen in presence of a very high mean signal density affecting a frequency range of the order of one Hertz, while when the signal cluster covers a frequency range of one tenth of Hertz, or less, we may actually have a sensitivity gain. Overall, we demonstrate the FH to be robust even in presence of moderate-to-large signal clusters

Direct constraints on ultra-light boson mass from searches for continuous gravitational waves

International audience\textit{Superradiance} can trigger the formation of an ultra-light 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 {\it 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 ultra-light scalar boson field mass

Probing new light gauge bosons with gravitational-wave interferometers using an adapted semicoherent method

International audienceWe adapt a method, originally developed for searches for quasimonochromatic, quasi-infinite duration gravitational-wave signals, to directly detect new light gauge bosons with laser interferometers, which could be candidates for dark matter. To search for these particles, we optimally choose the analysis coherence time as a function of boson mass, such that all of the signal power will be confined to one frequency bin. We focus on the dark photon, a gauge boson that could couple to the baryon or baryon-lepton number, and explain that its interactions with gravitational-wave interferometers result in a narrow-band, stochastic signal. We provide an end-to-end analysis scheme, estimate its computational cost, and investigate follow-up techniques to confirm or rule out dark matter candidates. Furthermore, we derive a theoretical estimate of the sensitivity, and show that it is consistent with both the empirical sensitivity determined through simulations, and results from a cross-correlation search. Finally, we place Feldman-Cousins upper limits using data from LIGO Livingston’s second observing run, which give a new and strong constraint on the coupling of gauge bosons to the interferometer

How effective is machine learning to detect long transient gravitational waves from neutron stars in a real search?

International audienceWe present a comprehensive study of the effectiveness of convolution neural networks (CNNs) to detect long-duration transient gravitational-wave signals lasting O(hours–days) from isolated neutron stars. We determine that CNNs are robust towards signal morphologies that differ from the training set, and they do not require many training injections/data to guarantee good detection efficiency and low false alarm probability. In fact, we only need to train one CNN on signal/noise maps in a single 150 Hz band; afterwards, the CNN can distinguish signals/noise well in any band, though with different efficiencies and false alarm probabilities due to the nonstationary noise in LIGO/Virgo. We demonstrate that we can control the false alarm probability for the CNNs by selecting the optimal threshold on the outputs of the CNN, which appears to be frequency dependent. Finally we compare the detection efficiencies of the networks to a well-established algorithm, the Generalized FrequencyHough (GFH), which maps curves in the time/frequency plane to lines in a plane that relates to the initial frequency/spin-down of the source. The networks have similar sensitivities to the GFH but are orders of magnitude faster to run and can detect signals to which the GFH is blind. Using the results of our analysis, we propose strategies to apply CNNs to a real search using LIGO/Virgo data to overcome the obstacles that we would encounter, such as a finite amount of training data. We then use our networks and strategies to run a real search for a remnant of GW170817, making this the first time ever that a machine learning method has been applied to search for a gravitational-wave signal from an isolated neutron star

Search for gravitational wave signals from known pulsars in LIGO-Virgo O3 data using the 5n-vector ensemble method

International audienceThe 5n-vector ensemble method is a multiple test for the targeted search of continuous gravitational waves from an ensemble of known pulsars. This method can improve the detection probability combining the results from individually undetectable pulsars if few signals are near the detection threshold. In this paper, we apply the 5n-vector ensemble method to the O3 data set from the LIGO and Virgo detectors considering an ensemble of 201 known pulsars. We find no evidence for a signal from the ensemble and set a 95% credible upper limit on the mean ellipticity assuming a common exponential distribution for the pulsars' ellipticities. Using two independent hierarchical Bayesian procedures, we find upper limits of $1.2 \times 10^{-9}$ and $2.5 \times 10^{-9}$ on the mean ellipticity for the 201 analyzed pulsars

Publisher’s Note: Observing gravitational-wave transient GW150914 with minimal assumptions [Phys. Rev. D 93, 122004 (2016)]

The gravitational-wave signal GW150914 was first identified on September 14, 2015, by searches forshort-duration gravitational-wave transients. These searches identify time-correlated transients in multipledetectors with minimal assumptions about the signal morphology, allowing them to be sensitive togravitational waves emitted by a wide range of sources including binary black hole mergers. Over theobservational period from September 12 to October 20, 2015, these transient searches were sensitive tobinary black hole mergers similar to GW150914 to an average distance of∼600Mpc. In this paper, wedescribe the analyses that first detected GW150914 as well as the parameter estimation and waveformreconstruction techniques that initially identified GW150914 as the merger of two black holes. We find thatthe reconstructed waveform is consistent with the signal from a binary black hole merger with a chirp massof∼30M⊙and a total mass before merger of∼70M⊙in the detector fram