Gravitational Radiation and Very Long Baseline Interferometry

Abstract

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

Gaia-like astrometry and gravitational waves

“…In this case a significant part of the effects of gravitational waves changes the proper motions of the sources and only a small part of the effects (if at all) goes to the residuals of an astrometric solution. The theory of these changes due to gravitational waves has been developed by a number of authors [2,3,39]. The theory was used to give upper estimates for the energy flux of the primordial gravitational waves using geodetic VLBI observations [15,36,45,46].…”

“…The deflection of a light ray due to a plane gravitational wave is discussed in details be many authors [2,39,41, and reference therein]. It is well known that the deflection of light due to a gravitational wave depends on the strain of the gravitational wave both at the observer and at the source of light.…”

“…Both Pyne et al [39] and Book & Flanagan [2] considered the case of an observer at rest, e.g. at the barycentre of solar system, so that the barycentric coordinates of the observer x obs vanish.…”

“…Using all these considerations the variation of the direction towards an astrometric source due to a plane gravitational wave can be written as [2,39] …”

“…The use of high-accuracy astrometry to detect various kinds of gravitational waves was discussed by many authors [2,3,15,31,36,39, and references therein]. The first subject of these studies was the effect of stochastic background of ultra-low-frequency primordial gravitational waves on the propagation of light as seen in astrometry, pulsar timing and other observational techniques.…”