C metric: the equatorial plane and Fermi coordinates

TL;DR

This paper analyzes photon trajectories and coordinate systems in the vacuum C metric, revealing similarities with Schwarzschild spacetime and providing coordinate mappings useful for estimating source parameters.

Contribution

It introduces a detailed study of geodesic motion in the C metric, highlighting the equatorial plane's properties and deriving coordinate transformations up to second order.

Findings

Photon trajectories on the equatorial plane resemble those in Schwarzschild spacetime with an energy shift.

Photons with zero angular momentum component remain confined on the hypersurface, unlike massive particles.

Explicit coordinate map between Bondi-like and Fermi coordinates is provided, aiding parameter estimation.

Abstract

We discuss geodesic motion in the vacuum C metric using Bondi-like spherical coordinates, with special attention to the role played by the "equatorial plane." We show that the spatial trajectory of photons on such a hypersurface is formally the same of photons on the equatorial plane of the Schwarzschild spacetime, apart from an energy shift involving the spacetime acceleration parameter. Furthermore, we show that photons starting their motion from this hypersurface with vanishing component of the momentum along $\theta$, remain confined on it, differently from the case of massive particles. This effect is shown to have a counterpart also in the massless limit of the C metric, i.e. in Minkowski spacetime. Finally, we give the explict map between Bondi-like spherical coordinates and Fermi coordinates (up to the second order) for the world line of an observer at rest at a fixed spatial point of the equatorial plane of the C metric, a result which may be eventually useful to estimate both the mass and the acceleration parameter of accelerated sources.