2015ApJ...807...89Z

Tidal disruption events (TDEs) can be perfect probes of dormant supermassive black holes in normal galaxies. During the rising phase, the accretion luminosity can increase by orders of magnitude in several weeks, and the emergent ionizing radiation illuminates the fresh accretion flow. In this paper, we simulated the evolution of the expected spectral line profile of iron due to such a flare by using a ray-tracing code with effects of general relativity taken into account. We found that the time-dependent profile changes significantly with black hole spin, inclination angle with respect to the black hole equatorial plane, and the expansion velocity of the ionization front. At low values of spin, a ''loop'' feature appears in the line profile versus time plot when the inclination is no less than 30° and the expansion velocity is no less than half the speed of light, owing to a shadow in the emission of the truncated disk. In the light curve two peaks occur depending on the inclination angle. At large, a shallow ''nose'' feature may develop ahead of the loop; its duration depends on the expansion velocity and the inclination angle. We explore the entire interval of black hole spin parameter ranging from extreme prograde to extreme retrograde rotation,. In the prograde case, a low-energy tail appears to be more pronounced in the evolving centroid energy of the line. Our results demonstrate the importance of searching for X-ray spectral lines in the early phase of TDE flares in order to constrain black hole mass and spin, as well as properties of the innermost accretion flow.