A Broad F[CLC]e[/CLC] Kα Emission Line in the X-Ray Spectrum of the Quasar 3C 273

The Fe-K line, an important physical diagnostic in the X-ray spectra of AGN,has been notoriously difficult to measure in the high-luminosity, radio-loudquasar 3C 273 (z=0.158). On the few occasions that it has been detected itsintrinsic width has been thought to be narrow (FWHM < 10,000 km/s) with anequivalent width (EW) of a few tens of eV.This was consistent with the generaltrend that as one goes from low to high luminosity AGNs the Fe-K line goes frombeing strong (EW ~200-300 eV) and broad (FWHM ~ 100,000 km/s) to being weak andnarrow, or absent altogether. Here we present the results of new ASCA and RXTEobservations, together with archival ASCA data, and show for the first timethat the Fe-K line in 3C 273 is as broad as that seen in Seyfert 1. The line isresolved in two of the observations, with a mean Gaussian width of 0.8 +/- 0.3keV, or FWHM of 0.3 +/- 0.1c. The smallest and largest EW measured is 43 +/- 34eV, and 133 (+52,-53) eV respectively (quasar frame). The Compton-reflectioncontinuum is less than 10% of that expected from a centrally illuminatedsemi-infinite, face-on, Compton-thick disk, confirming previous studies thatCompton reflection is negligible in 3C 273. The largest values of the Fe-K lineEW are under-predicted if the line originates in the disk, unless a time laglonger than several days between line and continuum and/or an over-abundance ofFe is invoked. We cannot unambiguously constrain the disk inclination angle.About 60 deg is preferred for a cold disk, while a face-on disk is allowed ifthe ionization state of Fe is H-like.Comment: 18 pages including 2 figures. Latex file picks up figures. (Accepted for Publication in the Astrophysical Journal Letters