Accretion Disc Thermal Reverberation in the Lamp Post Geometry

Abstract

We present results regarding the disc response functions and the corresponding time lags assuming a standard Novikov--Thorne accretion disc illuminated by a point-like X-ray source. We~took into account all relativistic effects in the light propagation from the X-ray source to the disc and then to the observer, and we computed the disc reflection, accounting for its radial ionization profile. Our~results suggest that the thermal reverberation effects should be stronger in sources with large X-ray source height and low accretion rate. We found that time lags increase with height and accretion rate. The amplitude of the observed time lags as a function of wavelength (in NGC 5548) is consistent with the model predictions. It is not necessary for the disc to be too hot, it may be that the X-ray source is located further from the disc.

Keywords

• galaxies: active
• galaxies: seyfert
• galaxies: individual (ngc 5548)
• x-rays: general