TY - JOUR
KW - accretion discs
KW - black holes
KW - galaxies
KW - quasars
KW - stars
AU - Jason Dexter
AU - Mitchell Begelman
AB - Rapid, large amplitude variability at optical to X-ray wavelengths is now seen in an increasing number of Seyfert galaxies and luminous quasars. The variations imply a global change in accretion power, but are too rapid to be communicated by inflow through a standard thin accretion disc. Such discs are long known to have difficulty explaining the observed optical/UV emission from active galactic nuclei. Here we show that alternative models developed to explain these observations have larger scale heights and shorter inflow times. Accretion discs supported by magnetic pressure in particular are geometrically thick at all luminosities, with inflow times as short as the observed few year time-scales in extreme variability events to date. Future time-resolved, multiwavelength observations can distinguish between inflow through a geometrically thick disc as proposed here, and alternative scenarios of extreme reprocessing of a central source or instability-driven limit cycles.
BT - Monthly Notices of the Royal Astronomical Society: Letters
DA - 2018-11
DO - 10.1093/mnrasl/sly213
N2 - Rapid, large amplitude variability at optical to X-ray wavelengths is now seen in an increasing number of Seyfert galaxies and luminous quasars. The variations imply a global change in accretion power, but are too rapid to be communicated by inflow through a standard thin accretion disc. Such discs are long known to have difficulty explaining the observed optical/UV emission from active galactic nuclei. Here we show that alternative models developed to explain these observations have larger scale heights and shorter inflow times. Accretion discs supported by magnetic pressure in particular are geometrically thick at all luminosities, with inflow times as short as the observed few year time-scales in extreme variability events to date. Future time-resolved, multiwavelength observations can distinguish between inflow through a geometrically thick disc as proposed here, and alternative scenarios of extreme reprocessing of a central source or instability-driven limit cycles.
PY - 2018
SP - L17 
EP -  L21
T2 - Monthly Notices of the Royal Astronomical Society: Letters
TI - Extreme AGN variability: evidence of magnetically elevated accretion?
UR - https://academic.oup.com/mnrasl/article/483/1/L17/5184476
VL - 483
SN - 1745-3925
ER -