On the peculiar X-ray properties of the bright nearby radio-quiet quasar PDS 456

BeppoSAX and ASCA observations of the nearby (z = 0.184), high-luminosity, radio-quiet quasar PDS 456 are presented. The X-ray spectrum is characteriz ed by a prominent ionized edge at 8-9 keV (originally discovered by RXTE, R eeves et al. 2000) and by a soft excess below 1.5 keV. The lack of any sign ificant iron K alpha emission line suggests for the edge an origin from lin e-of-sight material rather than from reflection from a highly ionized accre tion disc. The hard X-ray continuum is indeed well modelled by transmission through a highly-ionized medium with a large column density (N-Hwarm simil ar to 4.5 x 10(24) cm(-2)) plus an additional cold absorber with a lower co lumn density (N-Hcold similar to 2.7 x 10(22) cm(-2)).