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Hartmut Winkler — What the quasi-chaotic light curves of Active Galactic Nuclei can tell us about their inner being
Jul 22 @ 11:00 am - 12:00 pm
Thursday 22 July 2021
Hartmut Winkler (University of Johannesburg)
What the quasi-chaotic light curves of Active Galactic Nuclei can tell us about their inner being
50 years since Active Galactic Nuclei were first shown to be variable, the processes responsible for the luminosity changes are still not well understood. AGN light curves neither show much evidence of a pattern, nor is it clear why some appear more active than others. However, despite the chaotic appearance of the light curves, information can be extracted from these to unravel some of the structure and physical processes in operation near the central black hole. The talk explores results from the presenter’s recent spectral observations using the Sutherland 1.9 m telescope and photometry with the Las Cumbres Observatory global network. For the spectroscopy, these include the now ubiquitous reverberation mapping programmes and the search for “changing look” events (and tracking thereof). Several such dramatic spectral change events are presented and their significance is explored. The new photometry revives an old programme to determine nuclear colour and obscuration of AGN using multi-colour luminosity fluctuations, this time on a larger and fainter sample. This not only allows an improved AGN intrinsic luminosity determination, but sometimes even enables the characterisation of dust extinction around an AGN. Finally, growing evidence is presented of a sub-class of AGN that appears to have considerably more stable light curves than other sub-types, and potential reasons for this are explored.