Absorption features in the quasar HS 1603+3820 II. Distance to the
  absorber from photoionisation modelling
  We present photoionisation modelling of the intrinsic absorber in the bright
quasar HS 1603+3820. We construct spectral energy distribution using
optical/UV/X-ray observations as an input to photoionisation calculations.
Spectra from Keck telescope show extremely high ratio of CIV to HI, for the
first absorber in system A, named A1. This value, together with high column
density of CIV ion, puts strong constraints on photoionisation model. We use
photoionisation modeling to derive hydrogen number density at the cloud
illuminated surface. Estimating bolometric luminosity of HS 1603+3820, from
typical formula for quasars, we calculate the distance to A1. The derived
location is as close as 0.1 pc, and situates an absorber even closer to the
nucleus than the possible location of the Broad Line Region in this object
