What Kind of Obscured AGN Make the Cosmic X-ray Background?
  While it is understood that the origin of the Cosmic X-ray Background (CXRB) can be explained in terms of a combination of obscured and unobscured AGN, the identity of these obscured AGN showing up in large numbers at faint fluxes remains unclear. Deep surveys are showing up increasingly large numbers of AGN at the faintest fluxes which have broad optical lines but flat X-ray spectra. It is commonly assumed that there must a new population of sources making a substantial contribution to the CXRB. We show that we need not look further than our own backyard to find familiar examples of such sources and there is no compelling reason to invoke a mysterious, new population. 
T. Yaqoob (Laboratory for High Energy Astrophysics, NASA/GSFC)