Catching the Flare - Tracing Short-term AGN Outbursts via Daily Robotic Spectroscopy

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It is generally accepted that active galactic nuclei (AGN) are powered by the efficient accretion of matter onto supermassive black holes at their center. The resulting central ionizing radiation is variable on different time-scales, probably due to a discontinuous inflow of matter. According to the standard AGN paradigm, there are two structures, each with an extent of light-days to light-months, in the direct vicinity of the SMBH: (1) The accretion disk, which generates variable UV and optical continuum emission, and (2) the broad-line region (BLR), where the central and variable ionizing radiation generates likewise variable, but time-delayed broad-emission lines. Highly-variable AGN show extraordinarily strong variations in flux by more than 30 up to several 100 percent on extremely small time-scales of only days to months. “Changing-look AGN” are defined as AGN additionally exhibiting strong spectral changes of the broad-emission lines. However, current models of the AD and the BLR are not able to explain the short-term outbursts and variations, which are inconsistent with the standard model of a Shakura-Sunyaev accretion disc, observed in highly-variable and changing-look AGN. Evidently, current AD and BLR models need to be updated or extended with regard to their structure and kinematics to account for short-term variations in the continuum bands and line profiles. Here we propose to use Göttingen’s robotic MONET/South telescope, at our sole disposal, equipped with an integral field spectrograph to perform a daily-cadence spectroscopic and photometric monitoring campaign of a sample of ∼16 extraordinarily high-variable, and changing-look AGN. In parallel, we will – with the help of the ASAS-SN survey – watch 400 bright southern galaxies from the Revised Shapley-Ames Catalog on a weekly basis in order to look for additional highly-variable and changing-look AGN. The obtained continuum and line emission light-curves will be analysed by means of correlation techniques and result in high-quality information about the AD structure and the kinematics of the BLR. This project will be able to answer the question whether highly-variable and changing-look AGN exhibit a different structure and different kinematics, e.g., a time-dependent change of the inflow/outflow behaviour, than “normal” AGN, and lay the ground for updated models that take short-term variations into account.