SIMBAD references

We report a Chandra High-Energy Grating (HEG) detection of a narrow, redshifted absorption line superposed on the red wing of a broad Fe K line in the z=0.297 quasar E1821+643. The absorption line is detected at a confidence level, estimated by two different methods, in the range ∼2-3 σ. Although the detection significance is not high enough to exclude a nonastrophysical origin, accounting for the absorption feature when modeling the X-ray spectrum implies that the Fe K emission line is broad and consistent with an origin in a relativistic accretion disk. Ignoring the apparent absorption feature leads to the conclusion that the Fe K emission line is narrower and also affects the inferred peak energy of the line (and hence the inferred ionization state of Fe). If the absorption line (at ∼6.2 keV in the quasar frame) is real, then we argue that it could be due to gravitationally redshifted Fe XXV or Fe XXVI resonance absorption within ∼10-20 gravitational radii of the putative central black hole. The absorption line is not detected in earlier ASCA and Chandra Low-Energy Grating (LEG) observations, but the absorption line is not unequivocally ruled out by these data. The Chandra HEG Fe K emission line is consistent with an origin predominantly in Fe I-XVII or so. In an ASCA observation 8 years earlier, the Fe K line peaked at ∼6.6 keV, closer to the energies of He-like Fe triplet lines. Furthermore, in a Chandra LEG grating observation, the Fe K line profile was double peaked, one peak corresponding to Fe I-XVII or so and the other peak to Fe XXVI Lyα. Such a wide range in ionization states of Fe is not ruled out by the HEG and ASCA data either and is suggestive of a complex structure for the line emitter.