X-ray dips in the seyfert galaxy fairall 9: Compton-thick "cOMETS" or a failed radio galaxy?

Abstract

We investigate the spectral variability of the Seyfert galaxy Fairall 9 using almost 6years of monitoring with the Rossi X-ray Timing Explorer with an approximate time resolution of 4 days. We discover the existence of pronounced and sharp dips in the X-ray flux, with a rapid decline of the 2-20 keV flux of a factor of two or more followed by a recovery to pre-dip fluxes after ∼10 days. These dips skew the flux distribution away from the commonly observed lognormal distribution. Dips may result from the eclipse of the central X-ray source by broad-line region clouds, as has recently been found in NGC1365 and Mrk 766. Unlike these other examples, however, the clouds in Fairall 9 would need to be Compton-thick, and the non-dip state is remarkably free of any absorption features. A particularly intriguing alternative is that the accretion disk is undergoing the same cycle of disruption/ejection as seen in the accretion disks of broad-line radio galaxies such as 3C120 but, for some reason, fails to create a relativistic jet. This suggests that a detailed comparison of Fairall 9 and 3C120 with future high-quality data may hold the key to understanding the formation of relativistic jets in active galactic nucleus. © 2012 The American Astronomical Society. All rights reserved.