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T. Yaqoob (JHU/GSFC), I. M. George (UMBC/GSFC), T. Kallman (GSFC), U. Padmanabhan (JHU), K. A. Weaver (GSFC), T. J. Turner (UMBC/GSFC)
We report the detection of Fe~{\sc xxv} and Fe~{\sc xxvi} K\alpha emission lines from a Chandra HETGS observation of the narrow-line Seyfert~1 galaxy NGC~7314. The lines are redshifted (cz ~1500 \rm \ km \ s-1) and unresolved. The most viable geometry for the origin of the lines is a disk. The redshift and width constraints on Fe~{\sc xxvi}~Ly\alpha alone imply that the disk is within 7\circ of face-on, and that the line emission comes from within ~600 gravitational radii of the putative central black hole. These limits are model-independent: they not depend on the radial line emissivity, nor on how the continuum is modeled. The only requirement is that the Fe~{\sc xxvi}~Ly\alpha line indeed originates in a flat, Keplerian disk. The line emission may extend all the way down to a few gravitational radii and yet still give an overall line profile which is unresolved by Chandra if the disk is illuminated approximately uniformly (this is true also for the more common 6.4~keV K\alpha lines). The ionization balance of Fe responds to rapid continuum variations on timescales less than 12.5~ks -- unresolved emission from ionization states lower than Fe~{\sc xxv} appears when the continuum level is high. We also detect a constant, unresolved Fe~K\alpha line (EW~~80~eV) with a center energy consistent with the K\alpha line from Fe~{\sc i} to Fe~{\sc xvii} which is not redshifted, originating at >2.1 light days from the X-ray source. We present the results of a study of Fe~K\alpha lines in a Chandra HETGS sample of type~I AGN, including a search for Fe~{\sc xxv} and Fe~{\sc xxvi} K\alpha lines. These lines provide a more promising tool for measuring black-hole mass and spin than the low ionization-state fluorescent Fe~K\alpha lines since the ambiguity of ionization state is removed and there is no confusion with a non-disk line.
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The author(s) of this abstract have provided an email address for comments about the abstract: yaqoob@pha.jhu.edu
Bulletin of the American Astronomical Society,
35#2
© 2003. The American Astronomical Soceity.