Место издания:University of Southampton Southampton, UK
Первая страница:39
Последняя страница:39
Аннотация:As seen from the central source, the dusty torus of AGNs has a puzzlingly high covering factor. If the torus
consists of clouds of dust, each with a relatively unobscured view of the higher energy photons from nearer
the center of the AGN, the temperature of each dust cloud will fall o as roughly the inverse square root of
the radius. Since the dust is heated by the central radiation, in such a model the Near and Mid IR lag would
increase with the wavelength to a power of 2 to 2.8. We show that, contrary to this simple prediction, for a
signicant fraction of AGNs the lags of the J, H, K, and L bands with respect to the optical show at best only
a small dierence. This means that rather than there being an extended radial temperature gradient, the
hot dust reprocessing the central radiation is eectively in a relatively thin shell. We show that this can be
explained by the hot dust being on the surface of a cone that is approximately tangential to the paraboloidal
isodelay surface.
We note that a number of the AGNs showing similar J, H, K, and L lags are also Seyferts that have changed
between type 1 and type 2. It is not clear whether this is related or is merely a consequence of these objects
being well studied for a long time