Exploring long duration gravitational-wave transients with second generation detectors

Minute-long gravitational-wave (GW) transients are currently a little-explored regime, mainly due to a lack of robust models. As searches for long-duration GW transients must rely on minimal assumptions about the signal properties, they are also sensitive to GWs emitted from unpredicted sources. The detection of such sources offers exciting and strong potential for new science. Because of the large parameter space covered, all-sky long-duration transient searches require model-independant processing and fast analysis techniques. For my PhD thesis, I integrated a set of fast cross-correlation routines in the spherical harmonic domain (SphRad) [50] into X-pipeline [95], a targeted GW search pipeline commonly used to search for GW counterparts of short and long duration GRBs & core-collapse supernovae. Spherical harmonic decomposition allows for the sky position dependancy of the coherent analysis to be isolated from the data [40] and cached for re-use, saving both time and processing units. Moreover, the spherical harmonic approach offers a fundamentally different view of the data, allowing for new possibilities for rejecting non-Gaussian background noise that could be mistaken for a GW signal. The combined search pipeline, X-SphRad, underwent a thorough internal review within the LIGO collaboration, which I led. The pipeline good functioning was assessed by rigorous tests including comparing a test data set with a standard sky grid-based analysis. I have developed a novel pixel clustering method that does not depend on the amplitude of potential signals. By using an edge detection algorithm, I quantify each pixel in the spectrogram by its similarity with its neighbours then extract features of sharply changing intensity (or ‘edge’). The method has shown promising results in preliminary tests. A simplified version of the algorithm was implemented in X-SphRad and large-scale testings are currently being processed.

ALBUS: a machine learning algorithm for gravitational wave burst searches

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Optically targeted search for gravitational waves emitted by core-collapse supernovae during the first and second observing runs of advanced LIGO and advanced Virgo

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Search for continuous gravitational waves from neutron stars in globular cluster NGC 6544

We describe a directed search for continuous gravitational waves in data from the sixth initial LIGO science run. The target was the nearby globular cluster NGC 6544 at a distance of ≈2.7 kpc. The search covered a broad band of frequencies along with first and second frequency derivatives for a fixed sky position. The search coherently integrated data from the two LIGO interferometers over a time span of 9.2 days using the matched-filtering F-statistic. We found no gravitational-wave signals and set 95 confidence upper limits as stringent as 6.0\?x10-25 on intrinsic strain and 8.5\?x10-6 on fiducial ellipticity. These values beat the indirect limits from energy conservation for stars with characteristic spin-down ages older than 300 years and are within the range of theoretical predictions for possible neutron-star ellipticities. An important feature of this search was use of a barycentric resampling algorithm which substantially reduced computational cost; this method is used extensively in searches of Advanced LIGO and Virgo detector data

Supplement: The Rate Of Binary Black Hole Mergers Inferred From Advanced Ligo Observations Surrounding Gw150914

peer reviewedThis article provides supplemental information for a Letter reporting the rate of (BBH) coalescences inferred from 16 days of coincident Advanced LIGO observations surrounding the transient (GW) signal GW150914. In that work we reported various rate estimates whose 90 confidence intervals fell in the range 2-600 Gpc-3yr-1. Here we give details on our method and computations, including information about our search pipelines, a derivation of our likelihood function for the analysis, a description of the astrophysical search trigger distribution expected from merging BBHs, details on our computational methods, a description of the effects and our model for calibration uncertainty, and an analytic method for estimating our detector sensitivity, which is calibrated to our measurements

Search for intermediate mass black hole binaries in the first and second observing runs of the Advanced LIGO and Virgo network

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All-sky search for periodic gravitational waves in the O1 LIGO data

We report on an all-sky search for periodic gravitational waves in the frequency band 20-475 Hz and with a frequency time derivative in the range of [-1.0,+0.1]\?x10-8 Hz/s. Such a signal could be produced by a nearby spinning and slightly nonaxisymmetric isolated neutron star in our galaxy. This search uses the data from Advanced LIGO's first observational run, O1. No periodic gravitational wave signals were observed, and upper limits were placed on their strengths. The lowest upper limits on worst-case (linearly polarized) strain amplitude h0 are ∼4\?x10-25 near 170 Hz. For a circularly polarized source (most favorable orientation), the smallest upper limits obtained are ∼1.5\?x10-25. These upper limits refer to all sky locations and the entire range of frequency derivative values. For a population-averaged ensemble of sky locations and stellar orientations, the lowest upper limits obtained for the strain amplitude are ∼2.5\?x10-25

Results of the deepest all-sky survey for continuous gravitational waves on LIGO S6 data running on the Einstein@Home volunteer distributed computing project

peer reviewedWe report results of a deep all-sky search for periodic gravitational waves from isolated neutron stars in data from the S6 LIGO science run. The search was possible thanks to the computing power provided by the volunteers of the Einstein@Home distributed computing project. We find no significant signal candidate and set the most stringent upper limits to date on the amplitude of gravitational wave signals from the target population. At the frequency of best strain sensitivity, between 170.5 and 171 Hz we set a 90 confidence upper limit of 5.5\?x10-25, while at the high end of our frequency range, around 505 Hz, we achieve upper limits ≃10-24. At 230 Hz we can exclude sources with ellipticities greater than 10-6 within 100 pc of Earth with fiducial value of the principal moment of inertia of 1038 kg m2. If we assume a higher (lower) gravitational wave spin-down we constrain farther (closer) objects to higher (lower) ellipticities