Strong and Rapid X-Ray Variability of the Super-Eddington Accreting Quasar SDSS J081456.10+532533.5

Abstract

We report strong and rapid X-ray variability found from the super-Eddington accreting quasar SDSS J081456.10+532533.5 at z = 0.1197. It has a black hole mass of 2.7 × 10 ^7 M _⊙ and a dimensionless accretion rate of ≈4 measured from reverberation-mapping observations. It showed weak X-ray emission in the 2021 February Chandra observation, with the 2 keV flux density being ${9.6}_{-4.6}^{+11.6}$ times lower compared to an archival Swift observation. The 2 keV flux density is also ${11.7}_{-6.3}^{+9.6}$ times weaker compared to the expectation from its optical/UV emission. In a follow-up XMM-Newton observation 32 days later, the 2 keV flux density increased by a factor of ${5.3}_{-2.4}^{+6.4}$ , and the spectra are best described by a power law modified with partial-covering absorption; the absorption-corrected intrinsic continuum is at a nominal flux level. Nearly simultaneous optical spectra reveal no variability, and there is only mild long-term optical/infrared variability from archival data (with a maximum variability amplitude of ≈50%). We interpret the X-ray variability with an obscuration scenario, where the intrinsic X-ray continuum does not vary but the absorber has a variable column density and covering factor along the line of sight. The absorber is likely the small-scale clumpy accretion wind that has been proposed to be responsible for similar X-ray variability in other super-Eddington accreting quasars.

Keywords

• High energy astrophysics
• Quasars
• X-ray active galactic nuclei