Driving extreme variability: Measuring the evolving coronæ and evidence for jet launching in AGN

Relativistically blurred reflection from the accretion disc provides a powerful probe of the extreme environments close to supermassive black holes; the inner regions of the accretion flow and the corona that produces the intense X‐ray continuum. Techniques by which the geometry and extent of the corona can be measured through the observed X‐ray spectrum are reviewed along with the evolution in the structure of the corona that is seen to accompany variations in the X‐ray luminosity both on long and short timescales. Detailed analyses of the narrow line Seyfert 1 galaxies Mrk 335 and 1H 0707–495, over observations with XMM‐Newton as well as Suzaku and NuSTAR spanning nearly a decade reveal that increases in the X‐ray luminosity coincide with an expansion of the corona to cover a larger area of the inner accretion disc. Underlying this long timescale variability lie more complex patterns of behaviour on short timescales. Flares in the X‐ray emission during a low flux state of Mrk 335 observed in 2013 and 2014 are found to mark a reconfiguration of the corona while there is evidence that the flares were caused by a vertical collimation and ejection of coronal material, reminiscent of an aborted jet‐launching event. Measurements of the corona and reflecting accretion disc are combined to infer the conditions on the inner disc that lead to the flaring event. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)