Laura Duffy (Penn State U.): "Sleeping Giants: Telling Case Studies of Changing-look Quasars"

Changing-look quasars (CLQs) exhibit dramatic variability in their continuum strengths and broad emission-line fluxes on short timescales. This behavior is challenging to many models of the quasar accretion flow and the broad-line region, due in large part to the short transition times between high and low states. To investigate the cause of the observed transitions, in this talk I will present contemporaneous Hubble UV spectra and ground-based optical spectra of previously known turn-off CLQs. I will discuss the changing optical-UV spectral energy distributions of a few case studies before and after transition with an eye to predictions for quasars based on X-ray binary outbursts, which suggest that the mechanism for the change is likely a changing accretion flow structure. I will also discuss a few cases of CLQs that underwent multiple state changes, and what we can learn from both their SEDs and the timescale of the transitions, and the durations of the low and high states.