VARIABILITY OF THE Hβ LINE PROFILES AS AN INDICATOR OF ORBITING BRIGHT SPOTS IN ACCRETION DISKS OF QUASARS: A CASE STUDY OF 3C 390.3

Here we show that in the case when double-peaked emission lines originate from outer parts of the accretion disk, their variability could be caused by perturbations in the disk emissivity. In order to test this hypothesis, we introduced a model of the disk perturbing region in the form of a single bright spot (or flare) by a modification of the power-law disk emissivity in an appropriate way. The disk emission was then analyzed using numerical simulations based on the ray-tracing method in the Kerr metric and the corresponding simulated line profiles were obtained. We applied this model to the observed Hβ line profiles of 3C 390.3 (observed in the period 1995–1999) and estimated the parameters of both the accretion disk and the perturbing region. Our results show that two large amplitude outbursts of the Hβ line observed in 3C 390.3 could be explained by successive occurrences of two bright spots on the approaching side of the disk. These bright spots are either moving, originating in the inner regions of the disk and spiralling outward by crossing small distances during the period of several years, or stationary. In both cases, their widths increase with time, indicating that they most likely decay.