Ni, Q.Q.NiBrandt, W. N.W. N.BrandtYi, W.W.YiLuo, B.B.LuoTimlin, J. D., IIIJ. D., IIITimlinHall, P. B.P. B.HallLiu, HezhenHezhenLiuPlotkin, R. M.R. M.PlotkinShemmer, O.O.ShemmerVITO, FabioFabioVITOWu, JianfengJianfengWu2025-04-142025-04-1420202041-8205http://hdl.handle.net/20.500.12386/37067We 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.STAMPAenArticle10.3847/2041-8213/ab6d782-s2.0-85080907970https://iopscience.iop.org/article/10.3847/2041-8213/ab6d78https://api.elsevier.com/content/abstract/scopus_id/850809079702020ApJ...889L..37NFIS/05 - ASTRONOMIA E ASTROFISICA