Gravitational Radiation and Very Long Baseline Interferometry

Gravitational waves affect the observed direction of light from distant sources. At telescopes, this change in direction appears as periodic variations in the apparent positions of these sources on the sky; that is, as proper motion. A wave of a given phase, traveling in a given direction, produces a characteristic pattern of proper motions over the sky. Comparison of observed proper motions with this pattern serves to test for the presence of gravitational waves. A stochastic background of waves induces apparent proper motions with specific statistical properties, and so, may also be sought. In this paper we consider the effects of a cosmological background of gravitational radiation on astrometric observations. We derive an equation for the time delay measured by two antennae observing the same source in an Einstein-de Sitter spacetime containing gravitational radiation. We also show how to obtain similar expressions for curved Friedmann-Robertson-Walker spacetimes.Comment: 31 pages plus 3 separate figures, plain TeX, submitted to Ap

Quasar Proper Motions and Low-Frequency Gravitational Waves

We report observational upper limits on the mass-energy of the cosmological gravitational-wave background, from limits on proper motions of quasars. Gravitational waves with periods longer than the time span of observations produce a simple pattern of apparent proper motions over the sky, composed primarily of second-order transverse vector spherical harmonics. A fit of such harmonics to measured motions yields a 95%-confidence limit on the mass-energy of gravitational waves with frequencies <2e-9 Hz, of <0.11/h*h times the closure density of the universe.Comment: 15 pages, 1 figure. Also available at http://charm.physics.ucsb.edu:80/people/cgwinn/cgwinn_group/index.htm

Application of Millisecond Pulsar Timing to the Long-Term Stability of Clock Ensembles

Terrestrial timescales show instabilities due to the physical limitations of the atomic clocks. Stricter environmental isolation and increased numbers of improved cesium clocks and cavity-tuned hydrogen masers have resulted in time scales more accurate by a factor of about five. The use of different clock ensembles results in measurable changes in some millisecond pulsar timing data. We investigate the possible application of millisecond pulsars to define a precise long-term time standard and positional reference system in a nearly inertial reference frame. Although possible quantitative contribution of the two longest studied millisecond pulsars to terrestrial timescales appears minimal, they may prove useful as independent standards in identifying error sources that are difficult to detect due to the finite lifetime and common reference frame of terrestrial clocks. New millisecond pulsars, perhaps some with even better timing properties, may be discovered as a result of the current global pulsar search efforts. 1

Establishing Traceability with a GPS Disciplined Clock: A Preliminary Report

The metrological definition of traceability requires a documented and unbroken chain of calibrations that each contribute to the measurement uncertainty [1]. The calibrations must be end-to-end, which for a Global Positioning System Disciplined Clock (GPSDC), must include the antenna and cabling. While understanding legal definitions may be arduous at times, working with metrology labs to develop detailed criteria can be constructive for GPSDC manufacturers. To establish the suitability of a GPSDC for traceability, we have compared the one pulse-per-second (PPS) outputs of several GPSDCs to the National Institute of Standards and Technology (NIST) realization of Coordinated Universal Time, termed UTC(NIST). The GPSDC measurements included the use of several different antennas, with results showing agreement to within to tens of nanoseconds of UTC(NIST). We will explain these measurements and provide estimations of their associated uncertainties.International Foundation for TelemeteringProceedings from the International Telemetering Conference are made available by the International Foundation for Telemetering and the University of Arizona Libraries. Visit https://telemetry.org/contact-us/ if you have questions about items in this collection

Division A Commission 31: Time

International audienceTime is an essential element of fundamental astronomy. In recent years there have been many time-related issues, in scientific and technological aspects as well as in conventions and definitions. At the Commission 31 (Time) business meeting at the XXIX General Assembly, recent progress and many topics, including Pulsar Time Scales WG and Future UTC WG activities, were reviewed and discussed. In this report, we will review the progress of these topics in the past three years. There are many remarkable topics, such as Time scales, Atomic clock development, Time transfer, Future UTC and future redefinition of the second. Among them, scientific highlights are the progress of pulsar time scales and the optical frequency standards. On the other hand, as the social convention, change in the definition of UTC and the second is important