THE COMPLEX-X-RAY SPECTRA OF 2 HIGH-REDSHIFT QUASARS OBSERVED WITH ASCA

We report preliminary results of ASCA observations of two high-redshif t quasars (z approximately 3), PKS 0438-436 and PKS 2126-158. We find spectral flattening towards low energies in both sources, first found with ROSAT and interpreted as being due to excess X-ray absorption. Ho wever, the ROSAT data lacked the bandpass and sensitivity to unambiguo usly support this interpretation: We find that for PKS 2126-158, absor ption in intervening low-redshift material along the line-of-sight pro vides a statistically better description of the data than absorption i n material intrinsic to the quasar. The redshift of the putative absor ber is required to be less than a few tenths. Given the redshift const raints and the fact that absorption is not common in lower redshift qu asars, this result is not easily explained by a simple model. Either t he absorber may be complex or else the intrinsic X-ray spectrum may be complex, or both. Compton-reflection dominated models are ruled out b ut a broken power-law model provides good fits to the data without req uiring excess absorption. The break energy is at approximately 6-8 keV in the quasar frame and the energy index of the soft component is req uired to be extremely flat. This may mean that the X-ray emission in t hese objects is dominated by synchrotron losses as in BL Lac objects.