%0 Journal Article
%T A new population of soft X-ray weak quasars
%A G. Risaliti
%A A. Marconi
%A R. Maiolino
%A M. Salvati
%A P. Severgnini
%J Physics
%D 2001
%I arXiv
%R 10.1051/0004-6361:20010276
%X Quasars selected in optical surveys by means of their blue or UV excess are known to be strong emitters in the X-rays, except for Broad Absorption Line (BAL) objects. In this paper we study the X-ray emission of quasars selected through their emission line spectrum rather than their blue excess. X-ray data are obtained by cross-correlating two optical samples (the Hamburg Survey Catalogue and the Palomar Transit Catalogue) with the WGA catalogue of ROSAT observations. We find that a significant fraction of objects are strongly underluminous in the X-rays. We discuss the physical nature of these sources and we propose an interpretation for their optical and X-ray properties based on a dust-poor and gas-rich absorber. Our results suggest the existence of a population of AGNs having a type 1 optical spectrum and a type 2 X-ray emission
%U http://arxiv.org/abs/astro-ph/0102427v1