Photon surfing and magic speed revisited: Translucent effect

Abstract

Abstract Under the radiative environment of the intense radiation field around active phenomena such as black hole accretion disks, gaseous particles receive a strong radiative flux, which accelerates them, while they suffer from radiation drag by aberrated photons, which decelerates them. As a result, the acceleration of gaseous particles—photon surfing—would terminate at some magical speed βm(=v/c); (4-√7)/3 ∼ 0.45 for acceleration above an infinite flat radiator (Icke 1989, A&A, 216, 294). In a realistic gaseous cloud, part of the radiation would be absorbed by the cloud, some would be reflected, and some transmitted. We examine these translucent effects for a geometrically thin gaseous cloud (stratus). When the optical depth of the stratus is sufficiently large, the terminal speed is the well known magical speed βm for a particle. When the optical depth is around or less than unity, on the other hand, the terminal magical speed becomes large, up to ∼ 0.7c. This is just the translucent effect; the aberrated photons from the top of the stratus transmit the stratus much more than the direct photons from the bottom of the stratus facing the source.