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

The Fe Kα line, an important physical diagnostic in the X-ray spectra of active galaxies (AGNs) and quasars, has been notoriously difficult to measure in the high-luminosity, radio-loud quasar 3C 273 ( z = 0.158). On the few occasions that it has been detected, its intrinsic width has been thought to be narrow (FWHM < 10,000 km s -1 ), with an equivalent width (EW) of a few tens of eV. This was consistent with the general trend that as one goes from low- to high-luminosity AGNs, the Fe Kα line goes from being strong (EW ~ 200-300 eV) and broad (FWHM ~ 10 5 km s -1 ) to being weak and narrow, or absent altogether. Here we present the results of new ASCA and RXTE observations, together with archival ASCA data, and show for the first time that the Fe Kα line in 3C 273 is as broad as those seen in Seyfert 1 galaxies. The line is resolved in two of the observations, with a mean Gaussian width of 0.8 ± 0.3 keV, corresponding to a FWHM of ~0.3 ± 0.1 c . The smallest and largest equivalent widths measured are 43 and 133 eV, respectively (in the quasar frame). The Compton-reflection continuum is less than 10% of that expected from a centrally illuminated semi-infinite, face-on, Compton-thick disk, confirming previous studies that Compton reflection is negligible in 3C 273. The largest values of the Fe Kα line EW are underpredicted if the line originates in the disk, unless a time lag longer than several days between line and continuum and/or an overabundance of Fe is invoked. We cannot unambiguously constrain the disk inclination angle. About 60° is preferred for a cold disk, while a face-on disk is allowed if the ionization state of Fe is H-like.