THE COMPLEX-X-RAY SPECTRUM OF 3C-273 - ASCA OBSERVATIONS

The results obtained from 9 X-ray observations of 3C 273 performed by ASCA are presented (total exposure time similar to 160000 s). The anal ysis and interpretation of the data was complicated by the fact that 4 of these observations were used for the on-board calibration of the C CDs spectral response. The present standard analysis shows that, in ag reement with official recommendations, a conservative systematic error (at low energies) of 2-3 x 10(20) cm(-2) must be assumed when analyzi ng ASCA SIS data. A soft-excess, with variable flux and/or shape, has been clearly detected as well as flux and spectral variability. An ant i-correlation has been found between the spectral index and the flux i n the 2-10 keV energy range. Fitting the data with the latest availabl e calibration matrices, we also detect an emission line at 5.4-5.7 keV (6.3-6.6 keV in the quasar frame) in only the two observations with l owest fluxes where it is weak (EW similar to 20-30 eV), narrow and con sistent with being produced by Fe K alpha emission from neutral matter . Overall, the observations are qualitatively consistent with a variab le, non-thermal X-ray continuum emission (a power law with Gamma simil ar to 1.6, possibly produced in the innermost regions of the radio-opt ical jet), plus underlying ''Seyfert-like'' features (a soft-excess an d Fe K alpha line emission). When the continuum (jet) emission is in a low state, the Seyfert-like spectral features (soft-excess, iron line , and possibly a steep power law plus reflection continuum) are more e asily seen.