26-30 June 2023
Centro Congressi Federico II
Europe/Rome timezone

Extreme X-ray variability events of a weak-line quasar

Not scheduled
Aula Magna (Centro Congressi Federico II)

Aula Magna

Centro Congressi Federico II

Via Partenope, 36, Napoli, Italy
Poster Poster


Dr. Qingling Ni


We report the discovery of extreme X-ray variability events of the weak-line quasar SDSS J1539+3954 at z = 1.935. Before the X-ray flux rise (by a factor of > 20) observed in 2019, 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 was consistent with the majority of the AGN population. A flux drop by a factor of > 9 was observed nine months after the flux rise, and SDSS J1539+3954 became X-ray weak again. The HET spectra of SDSS J1539+3954 that are taken contemporaneously with X-ray observations show that its UV continuum level remains generally unchanged despite the dramatic variation 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 events may be caused by slight variations in the thickness of the disk across our line of sight.

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