Alessia Tortosa: Deep broad-band X-ray investigation of extreme accretion onto supermassive black holes

Super-Eddington accretion periods are expected to be extremely important to explain the fast growth of the first supermassive black holes (SMBHs). While standard optically thick, geometrically thin accretion discs explain the observed spectral energy distribution (SED) of many AGN with low Eddington ratios, at higher accretion rates the disc becomes thin or slim and the nature of the accretion changes dramatically. Slim accretion disks are thought to have SEDs that are different from thick accretion disks, with strong anisotropy of the emitted radiation and a large fraction of the output carried out in the form of outflows and jets capable of controlling the growth and evolution of the host galaxy, and affecting the gas reservoir available for both star formation and SMBH accretion.
Among all accretion modes, accretion close or above the Eddington limit is still the least understood ones, and it is still largely debated what are the physical properties of the X-ray emitting plasma and of the accretion flow coming from the direct relativistic environment of the SMBH.

I will present the first systematic broad-band X-ray study of extreme accretion onto SMBHs of a sample of Hyper and Super Eddington accreting AGN with 1 < λEdd < 426. These sources belong to the Super-Eddington Accreting Massive Black Holes sample, which contains exclusively objects with black hole masses estimated via reverberation mapping. This analysis allowed us to investigate the properties of the X-ray corona and the behaviour of the reprocessed radiation in this regime of extreme accretion, as well as the structure of the iron complex and the properties of outflows.