The signal from an emitting source moving in a Schwarzschild spacetime under the influence of a radiation field

TL;DR

This paper models the observational signals from a moving emitting source in Schwarzschild spacetime influenced by radiation drag, deriving flux, redshift, and images, and comparing with geodesic motion.

Contribution

It introduces a detailed calculation of signals from a source affected by radiation drag in Schwarzschild spacetime, extending previous models that assumed uniform photon angular momentum.

Findings

Derived flux, redshift, and solid angle as functions of time.

Produced the time-integrated image of the hot spot.

Compared effects with a source on a circular geodesic.

Abstract

The motion of matter immersed in a radiation field is affected by radiation drag, as a result of scattering or absorption and re-emission. The resulting friction-like drag, also known as Poynting-Robertson effect, has been recently studied in the general relativistic background of the Schwarzschild and Kerr metric, under the assumption that all photons in the radiation field possess the same angular momentum. We calculate here the signal produced by an emitting point-like specific source moving in a Schwarzschild spacetime under the influence of such a radiation field. We derive the flux, redshift factor and solid angle of the hot spot as a function of (coordinate) time, as well as the time-integrated image of the hot spot as seen by an observer at infinity. The results are then compared with those for a spot moving on a circular geodesic in a Schwarzschild metric.