
%0 Journal Article
%A Risaliti, G. 
%A Elvis, M. 
%A Nicastro, F. 
%T Ubiquitous Column Density Variability in Seyfert 2 Galaxies
%J Publications of the Astronomical Society of Australia
%D 2002/06/28
%V 19
%N 1
%P 155-157
%K galaxies: active &#8212; galaxies: Seyfert &#8212; X-rays: galaxies
%R https://doi.org/10.1071/AS01116
%U https://www.publish.csiro.au/paper/AS01116 
%X We present a study of X-ray column density variability in Seyfert 2 galaxies. We show that variations in NH are observed in almost all the objects with multiple hard X-ray observations. Variation timescales &#40;as short as a few months in several cases&#41; are not in agreement with the standard scenario of a parsec-scale toroidal absorber. We propose that the X-ray absorber in Seyfert galaxies is located much nearer to the centre than previously assumed, on the broad line region scale. An extension of the model by M. Elvis &#40;2000&#41; can explain the observed variability. We also show preliminary results of NH variability search inside single X-ray observations, which suggest that variations can occur on timescales of a few 104 s. 
