SIMBAD references

We present Chandra observations of 18 spectroscopically selected quasars, which are 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 active galactic nuclei needed in synthesis models of the X-ray background could instead be optical, broad-line, X-ray-weak quasars.