2007/10/25 by N. Sumitomo, Shinji Nishiyama, S. Nishiyama +6 · 1 citation
Physics and Astronomy · #Active galactic nucleus #Astronomy #Astrophysical Phenomena and Observations #Astrophysical jet #Astrophysics #Astrophysics and Cosmic Phenomena #Brightness #Classical mechanics #Electron #Galaxy #Gamma-ray bursts and supernovae #Inertial frame of reference #Luminosity #Photosphere #Physics #Radiation pressure #Relativistic beaming #Relativistic particle #Relativistic quantum chemistry #Relativistic speed #astro-ph.HE
paper · pdf · doi:10.1093/pasj/59.5.1043
published as PASJ, 59, 1043 (2007) · 6 pages, 6 figures
openalex publication_date 2007/10/25 · arxiv created 2009/04/18 · arxiv updated 2015/05/13 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
Abstract The photon mean free path in a relativistically moving medium becomes long in the downstream direction, while short in the upstream direction. As a result, the observed optical depth, τ, becomes small in the downstream direction while large in the upstream direction. Hence, if a relativistic spherical wind blows off, the optical depth depends strongly on its speed and the angle between the velocity and the line-of-sight. Abramowicz, Novikov, and Paczynski (1991, ApJ, 369, 175) examined such a relativistic wind, and found that the shape of the photosphere at τ=1 appears to be convex in the nonrelativistic case, but concave for relativistic velocities. We further calculated the temperature distribution and luminosity of the photosphere both in the comoving and inertial frames. We found that the limb-darkening effect would be strongly modified in the relativistic regime. We also found that the luminosities of the photosphere become large as the wind speed increases due to relativistic effects. In addition, the luminosity in the inertial frame is higher than that in the comoving frame. These results suggest that the observed temperature and brightness in luminous objects may be overestimated when there are strong relativistic winds.