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 $2.7\times 10^7{M}_{\odot }$ and a dimensionless accretion rate of $\approx 4$ 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 $\approx 50\%$). We interpret the X-ray variability with an obscuration scenario, where the intrinsic X-ray continuum does not vary but the absorber has 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.

16 pages, 8 figures, accepted for publication in ApJ

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