Variability of the H-beta line profiles as an indicator of orbiting bright spots in accretion disks of quasars: a case study of 3C 390.3

TL;DR

This study models the variability of H-beta line profiles in quasars, specifically 3C 390.3, by simulating bright spots in accretion disks to explain observed outbursts and their evolution.

Contribution

It introduces a novel disk perturbation model with bright spots to interpret emission line variability in quasars, supported by numerical ray-tracing simulations.

Findings

Bright spots can explain large amplitude outbursts in H-beta lines.

Bright spots may be moving or stationary, with decay indicated by increasing widths.

Model successfully fits observed line profile variations in 3C 390.3.

Abstract

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