Chandra observations of X-ray weak Quasars

We present Chandra observations of 18 spectroscopically selected quasars, already known to be X-ray weak from previous ROSAT observations. All the sources but one are detected by Chandra, and spectral analysis suggests that most of them are intrinsically underluminous in the X-rays (by a factor from 3 to >100). These objects could represent a large population of quasars with a Spectral Energy Distribution different from that of standard blue quasars. We discuss the possibility that a significant fraction of the obscured AGN needed in Synthesis models of the X-ray background could be instead optically broad-line, X-ray weak quasars.