The X-Ray Spectrum and Fe Kalpha Line of 3C 390.3, as Observed by ASCA

Details The X-Ray Spectrum and Fe Kalpha Line of 3C 390.3, as Observed by ASCA The X-Ray Spectrum and Fe Kalpha Line of 3C 390.3, as Observed by ASCA

Dec 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994aas...185.1815e&link_type=abstract

American Astronomical Society, 185th AAS Meeting, #18.15; Bulletin of the American Astronomical Society, Vol. 26, p.1340

Astronomy and Astrophysics

Astronomy

Scientific paper

We present the results of X-ray observations of the broad-line radio galaxy 3C 390.3 obtained with ASCA on 1993 Nov. 16. The 0.5--10 keV spectrum of the source is well described by a power-law plus an emission line, with no evidence for either a hard or a soft excess. The photon index is 1.70+/-0.05, and the absorbing column density is (9+/- 1)times 10(20) cm(-2) , which is somewhat larger than the neutral hydrogen column density in our Galaxy. The observed 2--10 keV flux is 1.6times 10(-11) erg cm(-2) s(-1) (+/-6%), which is a factor of 3 lower than the flux observed by Ginga in 1991 Nov.. An iron Kalpha line is unambiguously detected, with an equivalent width of 170+/-90 eV (90% confidence), and resolved. It has a centroid energy of 6.33+/-0.08 keV in the rest frame of the source, which is indicative of fluorescent emission from ``cold'' iron. The line width (FWHM of a Gaussian fit) is between 4,000 and 26,000 km s(-1) with 90% confidence. Alternatively, the line shape is consistent with that of the broad Hα line whose double peaks are separated by 8,000 km s(-1) . However, the signal-to-noise ratio of the X-ray data is not sufficient for a detailed study of its line profile. If the line width is attributed to Keplerian motion, then the emitting gas is located a few hundred gravitational radii or more from the central massive object. If the Fe Kalpha line originates in an accretion disk with inclination angle 26(deg) (estimated independently from model fits to the double-peaked Hα line, and from superluminal motions in the compact radio jet), then its measured equivalent width and centroid energy are in agreement with models for the reprocessing of X-rays from cool, dense material in the disk at a few hundred gravitational radii. An alternative origin of the Fe Kalpha line in the hot, innermost region of a disk is disfavored on the basis of the small velocity width, and centroid energy which is consistent with cold iron. It would also be difficult to attribute the X-ray line to fluorescence in ``standard'' broad-line region clouds because they would need to have N_H > 10(23) cm(-2) and a large covering fraction, which is not supported by the unabsorbed nature of the X-ray continuum.

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