An Extreme X-Ray Variability Event of a Weak-line Quasar
Date Issued
2020
Author(s)
Ni, Q.
•
Brandt, W. N.
•
Yi, W.
•
Luo, B.
•
Timlin, J. D., III
•
Hall, P. B.
•
Liu, Hezhen
•
Plotkin, R. M.
•
Shemmer, O.
•
•
Wu, Jianfeng
Abstract
We report the discovery of an extreme X-ray flux rise (by a factor of ≳20) of the weak-line quasar Sloan Digital Sky Survey (SDSS) J153913.47+395423.4 (hereafter SDSS J1539+3954) at z = 1.935. SDSS J1539+3954 is the most-luminous object among radio-quiet type 1 active galactic nuclei (AGNs) where such dramatic X-ray variability has been observed. Before the X-ray flux rise, SDSS J1539+3954 appeared X-ray weak compared with the expectation from its ultraviolet (UV) flux; after the rise, the ratio of its X-ray flux and UV flux is consistent with the majority of the AGN population. We also present a contemporaneous HET spectrum of SDSS J1539+3954, which demonstrates that its UV continuum level remains generally unchanged despite the dramatic increase in the X-ray flux, and its C IV emission line remains weak. The dramatic change only observed in the X-ray flux is consistent with a shielding model, where a thick inner accretion disk can block our line of sight to the central X-ray source. This thick inner accretion disk can also block the nuclear ionizing photons from reaching the high-ionization broad emission-line region, so that weak high-ionization emission lines are observed. Under this scenario, the extreme X-ray variability event may be caused by slight variations in the thickness of the disk. This event might also be explained by gravitational light-bending effects in a reflection model.
Volume
889
Issue
2
Start page
L37
Issn Identifier
2041-8205
Ads BibCode
2020ApJ...889L..37N
Rights
open.access
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