THE IRON K-ALPHA LINE-PROFILE IN NGC-4151

We present the first measurements of the Fe K alpha line profile in NG C 4151 from ASCA observations performed in 1993 May, November, and Dec ember. The apparent line profile is asymmetric, consisting of a peak a t similar to 6.3-6.4 keV, a sharp drop on the blue side below similar to 7 keV, and a broad red wing extending to similar to 4-5 keV. This f irst clear indication of complex structure confirms earlier tentative measurements of the Fe-K region with the Broad Band X-Ray Telescope (B BXRT). The line intensity, equivalent width, and detailed shape are mo del dependent. Interpretation of the profile in terms of emission from a disk rotating around a central black hole strongly constrains the p utative disk to be face on, but this contradicts the current body of k nowledge of the geometry of this source. If the apparent red wing is n ot in fact part of a peculiar continuum, then a face-on disk may be al lowed only if the collimated structure observed at the parsec scale is misaligned with respect to the disk normal by at least 20 degrees and iron is overabundant by a factor of similar to 2, with some additiona l caveats. Alternatively, a different geometry of line-emitting materi al may be required. In contrast to clear variability in the soft X-ray line emission below similar to 1 keV between the observations, these data show no significant variability of the Fe K alpha overall line sh ape, intensity, or equivalent width.