INAF - Osservatorio Astronomico di Padova -

 Relativistic Emission Lines from Accretion Disks around Supermassive Black Holes

Figure 1:Accretion disk image and computed line profiles.

 The observation of the broad relativistic iron Kalpha line in the active galactic nucleus MCG-6-30-15 stimulated the development of numerical codes that correctly take into account all relativistic effects near the vicinity of a black hole, in order to model such lines. They are nowadays considered to be born in an accretion disc around a supermassive black hole. The properties of iron lines lead directly to the observable properties of accretion discs and of black holes as well.

Figure 2:The upper panel shows the image of a geometrically thin accretion disk around a black hole with an angular momentum a=0.98 M, where M is the black hole mass. From left to right, disks of 10, 20, 40, 80, 160 gravitational radii are shown (inclination angle 55 deg). In the lower panel examples of computed emission line profiles are reported. Each of the four couple of images is for a non-rotating (left) and a rotating (right) black hole, with the following values of the other parameters: external disk radius 80 gravitational radii, power-law emissivity with exponent 0, 1, 2, 3. The color code of the line profiles reflects the contribution of different radial intervals with a step of 20 M.

 This motivated us to start a project for accurately calculating the profiles of relativistic emission lines from accretion disks around supermassive black holes in Active Galactic Nuclei. The main goal of this project is to produce images of the accretion disk (Figure 1) and determine the corresponding theoretical emission line profiles (in particular that of the fluorescent Fe Kalpha line; Figure 2). This computation is performed by exploiting the analytic integral solution of the geodetic photon equations in the general case of a rotating (Kerr) black hole derived by Čadež et al. (1998, New. Ast.). The code implementing this solution is very efficient and allows the user to specify various parameters, i.e. the angular momentum of the black hole, the external radius and inclination angle. It is capable to calculate lines produced by material extending below the marginally stable orbit and can handle various emissivity and illumination laws.

People: M. Calvani, P. Marziani

Collaboration: A. Čadež, A. Gomboc, U. Kostić (Ljubljana Univ., Slovenia) Publications: Čadež & Calvani (2005),  MNRAS 363,177; Čadež & Calvani (2006), AdSpR 38,1403

Link: Accretion disks around black holes