Shedding light on the X-ray weakness of the most luminous quasars

In our WISE/SDSSselected sample of hyperluminous (Lbol > 10^47 erg/s) quasars(WISSH) we are finding a sizable fraction of sources with strongly blueshiftedCIV emission lines (v_civ < 2000 km/s) and up to 1.5 dex lower Xray luminosity(L_X) compared to that reported for normal quasars. Based on a subsample of 13sources, we find that L_X and v_civ significantly correlate. No relation isfound at other bands. Furthermore, at low L_X, our constraints on Gamma and N_Hare insufficient to verify a dependence on v_CIV. We propose for XMMobservations to perform a complete Xray coverage for the remaining 9 WISSH QSOswith measured v_civ. These will allow a refined investigation enabling us todiscriminate between competing models for the origin of these sources. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]