Unabsorbed Seyfert 2 galaxies: the case of "naked" AGN
  Hawkins (2004) reported on a class of "naked" AGN characterized by strong
amplitude optical brightness variability and the complete absence of broad
emission lines in the optical spectrum. The variability suggests that the
nucleus is seen directly, however the absence of broad lines contradicts the
simple formulation of Unified Models for AGN. We present the results of
quasi-simultaneous spectroscopic observations with XMM-Newton and NTT (La
Silla) of two "naked" AGN. We confirm the "naked" nature of Q2131-427 for which
no broad emission line components have been detected in the optical spectrum
and its X-ray spectrum shows no signs of intrinsic absorption. The optical and
X-ray mismatch in this source cannot be ascribed to a high nuclear dust-to-gas
ratio and a Compton Thick nature is ruled out on the basis of the high
F(X)/F([OIII]) ratio. The Broad Line Region (BLR) may be completely absent in
this source, possibly as a consequence of its low Eddington ratio. On the other
hand, the optical spectrum of Q2130-431 shows H(alpha) and H(beta) broad
emission line components, revealing the presence of a BLR. A mild X-ray
absorption is expected in intermediate type 1.8 Seyfert galaxies like
Q2130-431, however we put a very low upper limit on the column density (< 2 x
10^(20) cm^(-2)), also the low Balmer decrement suggests that the BLR itself
does not suffer from reddening. We propose that in this object the BLR is
intrinsically weak, making a case of "true" intermediate Seyfert galaxy. We
also report on the X-ray detection of the Abell 3783 galaxy cluster in the
XMM-Newton field-of-view of the Q2131-427 observation.
