Simultaneous X-ray and optical observations of true Type 2 Seyfert galaxies. (arXiv:1209.0274v1 [astro-ph.GA])

Simultaneous X-ray and optical observations of true Type 2 Seyfert galaxies. (arXiv:1209.0274v1 [astro-ph.GA]):
We present the results of a campaign of simultaneous X-ray and optical
observations of `true' Type 2 Seyfert galaxies candidates, i.e. AGN without a
Broad Line Region (BLR). Out of the initial sample composed by 8 sources, one
object, IC1631, was found to be a misclassified starburst galaxy, another,
Q2130-431, does show broad optical lines, while other two, IRAS01428-0404 and
NGC4698, are very likely absorbed by Compton-thick gas along the line of sight.
Therefore, these four sources are not unabsorbed Seyfert 2s as previously
suggested in the literature. On the other hand, we confirm that NGC3147,
NGC3660, and Q2131-427 belong to the class of true Type 2 Seyfert galaxies,
since they do not show any evidence for a broad component of the optical lines
nor for obscuration in their X-ray spectra. These three sources have low
accretion rates ($\dot{m}= L_{bol}/L_{Edd} \la0.01$), in agreement with
theoretical models which predict that the BLR disappears below a critical value
of $L_{bol}/L_{Edd}$. The last source, Mrk273x, would represent an exception
even of this accretion-dependent versions of the Unification Models, due to its
high X-ray luminosity and accretion rate, and no evidence for obscuration.
However, its optical classification as a Seyfert 2 is only based on the absence
of a broad component of the H\beta, due to the lack of optical spectra
encompassing the H\alpha\ band.