X-ray/Optical Tracking of Changing-Look Quasars in SDSS-V

Changing-look quasars (CLQs) show dramatic changes in continuum luminosity, accompanied by the disappearance or appearance of broad line emission. The changing-look phenomena have been attributed to tidal disruption events, significant changes in intrinsic absorption or in accretion rate, but all these hypotheses suffer theoretical or empirical challenges. X-ray observations in both bright and faint states are the ideal probes for constraining both SMBH accretion rate and intrinsic absorption. About thirty thousand quasars are being monitored spectroscopically by the SDSS-V Black Hole Mapper program, where we are searching for real-time detection of CLQ transitions. Our Chandra ToO program (allocated up to 8 ToOs in Chandra Cycle 24 and 25) for newly-discovered CLQs with archival Chandra or XMM-Newton X-ray observations is characterizing CLQ changes in X-ray luminosity, slope, and intrinsic absorption. The X-ray flux generally changes along with the optical variability. Combining optical, X-ray, and VLA imaging, we test models with promising analogies to X-ray binary accretion variability. We acknowledge support from Chandra grants GO9-20086X and GO0-21084X.