Mohammed bin Salman. A monarch-to-be without scruples? Or a visionary seeking a path to global power? A social reformer determined to bring his country into the twenty-first century? Or just another ...brutal dictator? A leader on the road to greatness, or one destined to follow in the footsteps of Icarus? Veteran Washington Post foreign correspondent David Ottaway draws on more than a half-century of observation and reporting to shed light on these conundrums at the heart of any attempt to understand Saudi Arabia--and the man who is poised to rule the country for decades to come.
Isolated neutron stars are prime targets for continuous-wave (CW) searches by ground-based gravitational-wave interferometers. Results are presented from a CW search targeting ten pulsars. The search ...uses a semicoherent algorithm, which combines the maximum-likelihood F -statistic with a hidden Markov model (HMM) to efficiently detect and track quasi-monochromatic signals which wander randomly in frequency. The targets, which are associated with TeV sources detected by the High Energy Stereoscopic System (H.E.S.S.), are chosen to test for gravitational radiation from young, energetic pulsars with strong γ -ray emission, and take maximum advantage of the frequency tracking capabilities of HMM compared to other CW search algorithms. The search uses data from the second observing run of the Advanced Laser Interferometer Gravitational-Wave Observatory (aLIGO). It scans 1 − Hz sub-bands around f*, 4f*/3, and 2f*, where f* denotes the star's rotation frequency, in order to accommodate a physically plausible frequency mismatch between the electromagnetic and gravitational-wave emission. The 24 sub-bands searched in this study return 5,256 candidates above the Gaussian threshold with a false alarm probability of 1% per sub-band per target. Only 12 candidates survive the three data quality vetoes which are applied to separate non-Gaussian artifacts from true astrophysical signals. CW searches using the data from subsequent observing runs will clarify the status of the remaining candidates.
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Second generation gravitational wave detectors are being installed in a number of locations globally. These long-baseline, Michelson interferometers increase the sensitivity between 10 and 40 Hz by ...many orders of magnitude compared with first generation instruments. Control of non-linear noise coupling from scattered light fields is critical to achieve low frequency performance. In this paper we investigate the requirements on the attenuation of scattered light using a novel time-domain analysis and two years of seismic data from the LIGO Livingston Observatory.
Knowledge of the intensity and phase profiles of spectral components in a coherent optical field is critical for a wide range of high-precision optical applications. One of these is interferometric ...gravitational wave detectors, which rely on the optical beats between these fields for precise control of the experiment. Here we describe an optical lock-in camera and show that it can be used to record optical beats at MHz or greater frequencies with higher spatial and temporal resolution than previously possible. This improvement is achieved using a Pockels cell as a fast optical switch to transform each pixel on a sCMOS array into an optical lock-in amplifier. We demonstrate that the optical lock-in camera can record fields with 2 Mpx resolution at 10 Hz with a sensitivity of -62 dBc when averaged over 2s.
Third generation (3G) gravitational-wave detectors will observe thousands of coalescing neutron star binaries with unprecedented fidelity. Extracting the highest precision science from these signals ...is expected to be challenging owing to both high signal-to-noise ratios and long-duration signals. We demonstrate that current Bayesian inference paradigms can be extended to the analysis of binary neutron star signals without breaking the computational bank. We construct reduced-order models for ∼ 90 -min-long gravitational-wave signals covering the observing band (5–2048 Hz), speeding up inference by a factor of ∼ 1.3 × 104 compared to the calculation times without reduced-order models. The reduced-order models incorporate key physics including the effects of tidal deformability, amplitude modulation due to Earth's rotation, and spin-induced orbital precession. We show how reduced-order modeling can accelerate inference on data containing multiple overlapping gravitational-wave signals, and determine the speedup as a function of the number of overlapping signals. Thus, we conclude that Bayesian inference is computationally tractable for the long-lived, overlapping, high signal-to-noise-ratio events present in 3G observatories.
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