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Modern space measurement techniques like SLR, DORIS, VLBI and GNSS are used to study the tectonic plates. The determination of plate motion parameters (Φ, Λ, ω) from various geodetic measurements is outlined. This paper is the third part of our studies on estimating geodetic and geodynamic parameters; it regards an accuracy analysis of the determined Φ, Λ, ω parameters which describe motions of the tectonic plates using Very Long Base Interferometry (VLBI) technique. Prior to this, SLR and DORIS space measurement techniques were examined by authors. The study is based on the velocities of station positions, as included in a realization of the International Terrestrial Reference System– ITRF2008 forVLBI technique, published by the International Earth Rotation and Reference Systems Service (IERS). This model is made subject to an analysis in association with the APKIM2005 model. Six big plates, namely: Eurasian (EUAS), African (AFR), Australian (AUS), North American (NOAM), Pacific (PACF) and Antarctic (ANTC) were analysed. The results obtained in this analysis were compared with our previous estimations based on DORIS and SLR techniques and estimated according to the APKIM2005 model. Generally, all our three solutions based on SLR, DORIS and VLBI measurement techniques were found to be consistent.

The binary neutron star merger event GW170817 was detected through both electromagnetic radiation and gravitational waves. Its afterglow emission may have been produced by either a narrow relativistic jet or an isotropic outflow. High-spatial-resolution measurements of the source size and displacement can discriminate between these scenarios. We present very-long-baseline interferometry observations, performed 207.4 days after the merger by using a global network of 32 radio telescopes. The apparent source size is constrained to be smaller than 2.5 milli–arc seconds at the 90% confidence level. This excludes the isotropic outflow scenario, which would have produced a larger apparent size, indicating that GW170817 produced a structured relativistic jet. Our rate calculations show that at least 10% of neutron star mergers produce such a jet.

Gravitational waves have been detected from a binary neutron star merger event, GW170817. The detection of electromagnetic radiation from the same source has shown that the merger occurred in the outskirts of the galaxy NGC 4993, at a distance of 40 megaparsecs from Earth. We report the detection of a counterpart radio source that appears 16 days after the event, allowing us to diagnose the energetics and environment of the merger. The observed radio emission can be explained by either a collimated ultrarelativistic jet, viewed off-axis, or a cocoon of mildly relativistic ejecta. Within 100 days of the merger, the radio light curves will enable observers to distinguish between these models, and the angular velocity and geometry of the debris will be directly measurable by very long baseline interferometry.

We describe the process to design, architect, and implement a transformative enhancement of the Event Horizon Telescope (EHT). This program—the next-generation Event Horizon Telescope (ngEHT)—will form a networked global array of radio dishes capable of making high-fidelity real-time movies of supermassive black holes (SMBH) and their emanating jets. This builds upon the EHT principally by deploying additional modest-diameter dishes to optimized geographic locations to enhance the current global mm/submm wavelength Very Long Baseline Interferometric (VLBI) array, which has, to date, utilized mostly pre-existing radio telescopes. The ngEHT program further focuses on observing at three frequencies simultaneously for increased sensitivity and Fourier spatial frequency coverage. Here, the concept, science goals, design considerations, station siting, and instrument prototyping are discussed, and a preliminary reference array to be implemented in phases is described.

The binary neutron-star merger GW170817 1 was accompanied by radiation across the electromagnetic spectrum 2 and localized 2 to the galaxy NGC 4993 at a distance 3 of about 41 megaparsecs from Earth. The radio and X-ray afterglows of GW170817 exhibited delayed onset 4 – 7 , a gradual increase 8 in the emission with time (proportional to t 0.8 ) to a peak about 150 days after the merger event 9 , followed by a relatively rapid decline 9 , 10 . So far, various models have been proposed to explain the afterglow emission, including a choked-jet cocoon 4 , 8 , 11 – 13 and a successful-jet cocoon 4 , 8 , 11 – 18 (also called a structured jet). However, the observational data have remained inconclusive 10 , 15 , 19 , 20 as to whether GW170817 launched a successful relativistic jet. Here we report radio observations using very long-baseline interferometry. We find that the compact radio source associated with GW170817 exhibits superluminal apparent motion between 75 days and 230 days after the merger event. This measurement breaks the degeneracy between the choked- and successful-jet cocoon models and indicates that, although the early-time radio emission was powered by a wide-angle outflow 8 (a cocoon), the late-time emission was most probably dominated by an energetic and narrowly collimated jet (with an opening angle of less than five degrees) and observed from a viewing angle of about 20 degrees. The imaging of a collimated relativistic outflow emerging from GW170817 adds substantial weight to the evidence linking binary neutron-star mergers and short γ-ray bursts. Emission from the radio counterpart of the gravitation-wave event GW170817 was powered by a wide-angle outflow at early times, but probably dominated by a narrowly collimated jet at later times.

Powerful relativistic jets are one of the main ways in which accreting black holes provide kinetic feedback to their surroundings. Jets launched from or redirected by the accretion flow that powers them are expected to be affected by the dynamics of the flow, which for accreting stellar-mass black holes has shown evidence for precession 1 due to frame-dragging effects that occur when the black-hole spin axis is misaligned with the orbital plane of its companion star 2 . Recently, theoretical simulations have suggested that the jets can exert an additional torque on the accretion flow 3 , although the interplay between the dynamics of the accretion flow and the launching of the jets is not yet understood. Here we report a rapidly changing jet orientation—on a time scale of minutes to hours—in the black-hole X-ray binary V404 Cygni, detected with very-long-baseline interferometry during the peak of its 2015 outburst. We show that this changing jet orientation can be modelled as the Lense–Thirring precession of a vertically extended slim disk that arises from the super-Eddington accretion rate 4 . Our findings suggest that the dynamics of the precessing inner accretion disk could play a role in either directly launching or redirecting the jets within the inner few hundred gravitational radii. Similar dynamics should be expected in any strongly accreting black hole whose spin is misaligned with the inflowing gas, both affecting the observational characteristics of the jets and distributing the black-hole feedback more uniformly over the surrounding environment 5 , 6 . The relativistic jets associated with the black-hole X-ray binary system V404 Cygni change their orientation on time scales of minutes to hours, implying that the direction of the jets is being affected by the dynamics of the surrounding accretion flow that powers them.

The afterglow of the binary neutron-star merger GW170817 1 gave evidence for a structured relativistic jet 2 – 6 and a link 3 , 7 , 8 between such mergers and short gamma-ray bursts. Superluminal motion, found using radio very long baseline interferometry 3 (VLBI), together with the afterglow light curve provided constraints on the viewing angle (14–28 degrees), the opening angle of the jet core (less than 5 degrees) and a modest limit on the initial Lorentz factor of the jet core (more than 4). Here we report on another superluminal motion measurement, at seven times the speed of light, leveraging Hubble Space Telescope precision astrometry and previous radio VLBI data for GW170817. We thereby obtain a measurement of the Lorentz factor of the wing of the structured jet, as well as substantially improved constraints on the viewing angle (19–25 degrees) and the initial Lorentz factor of the jet core (more than 40). Optical superluminal motion in the binary neutron-star merger GW170817 is used to constrain the speed and morphology of the structured jet, and improve constraints on the inclination angle of the merging binary system.

An exact knowledge of the instantaneous Earth’s rotation rate is indispensable for accurate navigation and geolocation. Fluctuations in the length of sidereal day are caused by momentum exchange between the fluids of the Earth (namely, the atmosphere, hydrosphere and cryosphere) and the solid Earth. Since a multitude of different globally distributed and independent mass transport phenomena are involved, the resultant effect on the Earth’s rotation is not predictable and needs to be continuously measured. Here we report the observation of minute variations in the rotation rate of the Earth at the level of five parts per billion, namely, with a resolution of a few milliseconds over 120 days of continuous measurements. We employ an inertial self-contained measurement technique based on an optical ring laser interferometer rigidly strapped down to the Earth’s crust and operated in the Sagnac configuration. This large-scale gyroscope integrates over three hours for each data point, as opposed to an entire global network of Global Navigation Satellite Systems receivers and Very Long Baseline Interferometry that can only provide a single measurement per day.A self-contained ring laser interferometre measures length-of-day variations due to global mass transport phenomena with a precision of a few milliseconds over several months of measurements.

Blazars are a sub-class of quasars with Doppler boosted jets oriented close to the line of sight, and thus efficient probes of supermassive black hole growth and their environment, especially at high redshifts. Here we report on Very Long Baseline Interferometry observations of a blazar J0906 + 6930 at z  = 5.47, which enabled the detection of polarised emission and measurement of jet proper motion at parsec scales. The observations suggest a less powerful jet compared with the general blazar population, including lower proper motion and bulk Lorentz factor. This coupled with a previously inferred high accretion rate indicate a transition from an accretion radiative power to a jet mechanical power based transfer of energy and momentum to the surrounding gas. While alternative scenarios could not be fully ruled out, our results indicate a possibly nascent jet embedded in and interacting with a dense medium resulting in a jet bending. High redshift blazars are efficient probes of supermassive black holes and their environment in the early Universe. Here the authors show measurements of polarised emission and proper motion in the blazar J0906+6930 (redshift of 5.47) characterised by a nascent jet embedded in and interacting with a dense medium.

The hyperfine splitting of antihydrogen has been measured and is consistent with expectations for atomic hydrogen. Assessing the antihydrogen spectrum Comparing precision measurements of hydrogen with equivalent measurements of antihydrogen is a way of testing charge–parity–time (CPT) symmetries, which are fundamental to physics. However, the fragility of antihydrogen makes it very difficult to produce in sufficient quantities to perform spectroscopic measurements. Here, the authors use a new antihydrogen accumulation technique, which allows for measuring the hyperfine spectrum of antihydrogen. The results reveal no differences between hydrogen and antihydrogen. As the spectrum of hydrogen is known very well and to high precision, experimental improvements could yield extremely precise tests of the CPT theorem. The observation of hyperfine structure in atomic hydrogen by Rabi and co-workers 1 , 2 , 3 and the measurement 4 of the zero-field ground-state splitting at the level of seven parts in 10 13 are important achievements of mid-twentieth-century physics. The work that led to these achievements also provided the first evidence for the anomalous magnetic moment of the electron 5 , 6 , 7 , 8 , inspired Schwinger’s relativistic theory of quantum electrodynamics 9 , 10 and gave rise to the hydrogen maser 11 , which is a critical component of modern navigation, geo-positioning and very-long-baseline interferometry systems. Research at the Antiproton Decelerator at CERN by the ALPHA collaboration extends these enquiries into the antimatter sector. Recently, tools have been developed that enable studies of the hyperfine structure of antihydrogen 12 —the antimatter counterpart of hydrogen. The goal of such studies is to search for any differences that might exist between this archetypal pair of atoms, and thereby to test the fundamental principles on which quantum field theory is constructed. Magnetic trapping of antihydrogen atoms 13 , 14 provides a means of studying them by combining electromagnetic interaction with detection techniques that are unique to antimatter 12 , 15 . Here we report the results of a microwave spectroscopy experiment in which we probe the response of antihydrogen over a controlled range of frequencies. The data reveal clear and distinct signatures of two allowed transitions, from which we obtain a direct, magnetic-field-independent measurement of the hyperfine splitting. From a set of trials involving 194 detected atoms, we determine a splitting of 1,420.4 ± 0.5 megahertz, consistent with expectations for atomic hydrogen at the level of four parts in 10 4 . This observation of the detailed behaviour of a quantum transition in an atom of antihydrogen exemplifies tests of fundamental symmetries such as charge–parity–time in antimatter, and the techniques developed here will enable more-precise such tests.