Witnessing the key early phase of quasar evolution: an obscured AGN pair
  in the interacting galaxy IRAS 20210+1121
  We report the discovery of an active galactic nucleus (AGN) pair in the
interacting galaxy system IRAS 20210+1121 at z = 0.056. An XMM-Newton
observation reveals the presence of an obscured (Nh ~ 5 x 10^{23} cm^-2),
Seyfert-like (L_{2-10 keV} = 4.7 x 10^{42} erg/s) nucleus in the northern
galaxy, which lacks unambiguous optical AGN signatures. Our spectral analysis
also provides strong evidence that the IR-luminous southern galaxy hosts a Type
2 quasar embedded in a bright starburst emission. In particular, the X-ray
primary continuum from the nucleus appears totally depressed in the XMM-Newton
band as expected in case of a Compton-Thick absorber, and only the emission
produced by Compton scattering ('reflection') of the continuum from
circumnuclear matter is seen. As such, IRAS 20210+1121 seems to provide an
excellent opportunity to witness a key, early phase in the quasar evolution
predicted by the theoretical models of quasar activation by galaxy collisions.
