2008/10/25 by Jun Fukue, J. Fukue
Physics and Astronomy · #Anisotropy #Astrophysical Phenomena and Observations #Astrophysics and Cosmic Phenomena #Background radiation #Eddington luminosity #Flow (mathematics) #Flow velocity #Laser-Plasma Interactions and Diagnostics #Observer (physics) #Radiation #Radiation pressure #Relativistic particle #Velocity gradient #astro-ph.HE
paper · pdf · doi:10.1093/pasj/60.5.1209
published as PASJ, 60, 1209 (2008) · 8 pages, 7 figures
openalex publication_date 2008/10/25 · arxiv created 2009/04/18 · arxiv updated 2015/05/13 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
We examine the Eddington factor in an optically thick, relativistic flow accelerating in the vertical direction. When the gaseous flow is radiatively accelerated and there is a velocity gradient, there also exists a density gradient. The comoving observer sees radiation coming from a closed surface where the optical depth measured from the observer is unity. Such a surface, called a one-tau photo-oval, is elongated in the flow direction. In general, the radiation intensity emitted by the photo-oval is non-uniform, and the photo-oval surface has a relative velocity with respect to the position of the comoving observer. Both effects introduce some degree of anisotropy in the radiation field observed in the comoving frame. As a result, the radiation field observed by the comoving observer becomes anisotropic, and the Eddington factor must deviate from the usual value of 1/3. Thus, the relativistic Eddington factor generally depends on the optical depth τ and the velocity gradient du/dτ, u being the four velocity. In the case of a plane-parallel vertical flow, we obtained the shape of the photo-oval and calculated the Eddington factor in the optically thick regime. We found that the Eddington factor f can be well approximated by f(τ, (du)/(dτ)) = (1)/(3) exp ( (1)/(u) (du)/(dτ) ) . This relativistic variable Eddington factor can be used in various relativistic radiatively-driven flows.