XMM-Newton Observations of Two Archival X-ray Weak Type 1 Quasars: Obscuration Induced X-ray Weakness and Variability
Abstract
We report XMM-Newton observations of two examples of an unclassified type of X-ray weak quasars from the 2020ApJ...900..141P survey of X-ray weak quasars in the Chandra archive, SDSS J083116.62+321329.6 at z=1.797 and SDSS J142339.87+042041.1 at z=1.702. They do not belong to the known populations of X-ray weak quasars that show broad absorption lines, weak ultraviolet (UV) broad emission lines, or red optical/UV continua. Instead, they display typical quasar UV spectra and spectral energy distributions. In the XMM-Newton observations, both quasars show nominal levels of X-ray emission with typical quasar X-ray spectral shapes (power-law photon indices of 1.99+0.27-0.23 and 1.86+0.15-0.14), displaying strong X-ray variability compared to the archival Chandra data (variability factors of 4.0+1.6-1.4 and 9.0+7.4-3.8 in terms of the 2 keV flux density). Simultaneous optical (rest-frame UV) spectra indicate no strong variability compared to the archival spectra. Long-term optical/UV and infrared light curves do not show any substantial variability either. We consider that the X-ray weakness observed in the Chandra data is due to X-ray obscuration from a small-scale dust-free absorber, likely related to accretion-disk winds. Such X-ray weak/absorbed states are probably rare in typical quasars, and thus both targets recovered to X-ray nominal-strength states in the XMM-Newton observations.
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