Speaker
Description
The high luminosities of quasars are thought to originate in an accretion disk that surrounds a black hole. The broad line region (BLR) that lies at ~10x larger radii is also known to be ionized by UV radiation from the accretion disk to produce the broad emission lines. But previously there has been no evidence of any reprocessing of X-rays that might allow the BLR to re-radiate the accretion disk. Here, using eROSITA eFEDS data we show that the X-ray emission is crucial to a new understanding of a self-perpetuating process for quasar fuelling. Using stacked reverberation mapping, we first find that the radius of the quasar BLR is ~35 light days for CIV. Using the same technique, we find a similar ~35-day lag for continuum-X-ray cross-correlations, with the X-rays unexpectedly lagging the continuum. Further, we find a still longer ~90-day cross-correlation where the continuum now lags the X-ray. Both lags are longer than expected from an accretion disk of ~3 light days extent. We conclude that the quasar BLR reflects light back to the accretion disk, continuously stimulating further accretion disk activity and also causing the reflection features seen in quasar X-ray spectra.
