Results obtained from 9 X-ray observations of 3C 273 performed by ASCA are presented ( for a total exposure time of about 160 000 s ) .
The analysis and interpretation of the results is complicated by the fact that 4 of these observations were used for on-board calibration of the CCDs spectral response .
In particular , we had to pay special attention to the low energy band and 5–6 keV energy range where systematic effects could distort a correct interpretation of the data .

The present standard analysis shows that , in agreement with official recommendations , a conservative systematic error ( at low energies ) of \sim 2–3 \times 10 ^ { 20 } cm ^ { -2 } must be assumed when analyzing ASCA SIS data .
A soft-excess , with variable flux and/or shape , has been clearly detected as well as flux and spectral variability that confirm previous findings with other observatories .
An anti-correlation is found between the spectral index and the flux in the 2-10 keV energy range .
With the old response matrices , an iron emission line feature with EW \sim 50–100 eV was initially detected at \sim 5.6-5.7 keV ( \sim 6.5-6.6 keV in the quasar frame ) in 6 observations and , in two occasions , the line was resolved ( \sigma \sim 0.2-0.6 keV ) .
Comparison with the Crab spectrum indicates however that this feature was mostly due to remaining calibration uncertainties between 5–6 keV .
Indeed , fitting the data with the latest publicly available calibration matrices , we find that the line remains unambiguously significant in ( only ) the two observations with lowest fluxes where it is weak ( EW \sim 20-30 eV ) , narrow and consistent with being produced by Fe K _ { \alpha } emission from neutral matter .

Overall , the observations are qualitatively consistent with a variable , non-thermal X-ray continuum emission , i.e. , a power law with \Gamma \sim 1.6 ( possibly produced in the innermost regions of the radio-optical jet ) , plus underlying “ Seyfert-like ” features , i.e. , a soft-excess and Fe K _ { \alpha } line emission .
The data are consistent with some contribution ( up to a few 10 % level in the ASCA energy band ) from a “ Seyfert-like ” direct continuum emission , i.e .
a power law with \Gamma \sim 1.9 plus a reflection component , as well .
When the continuum ( jet ) emission is in a low state , the spectral features produced by the Seyfert-like spectrum ( soft-excess , iron line and possibly a steep power law plus a reflection continuum ) are more easily seen .