Observational Appearance of Optically Thick, Relativistic Winds
Sumitomo Naoko,Fukue Jun,Watarai Ken-ya
Astronomical Institute, Osaka Kyoiku University, Asahigaoka, Kashiwara, Osaka 582-8582
Abstract
Abramowicz et al. (1991) examined a relativistic wind, and found that the shape of the photosphere appears convex in the non-relativistic case, but concave for relativistic velocities. We further calculated the temperature distribution and luminosity of the photosphere both in the co-moving and inertial frames. We found that the limb-darkening effect would strongly modified in the relativistic regime. We also found that luminosities of the photosphere becomes large as the wind speed increases due to the relativistic effects. In addition, the luminosity in the inertial frame is higher than that in the co-moving frame. These results suggest that the observed temperature and brightness in luminous objects may be overestimated.
1. Introduction
The outflow which is driven by radiation-pressure has been observed in luminous Galactic black-hole candidates, active galactic nuclei (AGNs), and distant quasars.When we observe such objects, the last scattered surface of photons may be changed by the wind, i.e., the disk is concealed by the wind when the wind matter ishighly optically thick. In that case, we can obtain the information of the photosphere.
2. Calculation Method
・Co-moving rest mass density
・Black hole mass = 107 M☉,Temperature (at the central region) = 107 K
・The opacity was dominated by electron scattering.
・The optical depth to photosphere
・The temperature in the co-moving frame ・The temperature in the observer’s frame
・The luminosity in the observer’s frame
3. Result & Discussion
Result 1 Location of the photosphere for various wind velocity
Result 2Temperature distribution of photosphere
Result 3Luminosity in the co-moving frame (broken line)and in the observer’s frame (solid line).
The observed shape of
the photosphere is asymmetric.This is due to the limb-darkening effect. Due to the optical depth effect,we could see deeper inside the wind, as the velocity increases.In addition, the luminosity in the observer's frame is remarkably enhanced by relativistic beaming effects along the observer's direction. These two effects mainly work as the luminosity enhancement of the relativistic outflow. This fact shows the possibility of overestimation of the temperature and the luminosity of the object that is supposed for wind to blow off at a relativistic speed.When the wind velocity is fast or the mass-loss rate is small, the radius on a bright photosphere becomes small, and we observe higher temperature and higher luminosity.There is possibility that the estimate of luminosity and black hole mass different from those actual values.
Sumitomo, N. et al 2007, PASJ, 59