086126

Luminous X-ray emission is an ubiquitous property of quasars. Small populations of type 1 quasars have displayed weak X-ray emission comma generally due to absorption or variability effects. We have discovered several X-ray weak SDSS quasars that do not fit easily into any of the known categories. We propose to obtain 30-50 ks XMM-Newton observations for three of these exceptional X-ray weak quasars. We will determine reliably whether there is X-ray variability or X-ray absorption comma and then classify the possible causes for their observed X-ray weakness. Understanding this new type of X-ray weak quasar might provide new insights into the X-ray corona and its environment. It will also allow us to constrain the missed fraction of SMBH growth in extragalactic X-ray surveys.