Astronomy and Astrophysics – Astrophysics
Scientific paper
2005-02-06
Astrophys.J. 623 (2005) 112-122
Astronomy and Astrophysics
Astrophysics
To be published in the Astrophysical Journal, 20 April 2005. 18 pages, ten figures, five of them in color. Four tables. Abstra
Scientific paper
10.1086/428432
We report a Chandra high-energy grating detection of a narrow, redshifted absorption line superimposed 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 sigma. Although the detection significance is not high enough to exclude a non-astrophysical 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, 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 low-energy grating observations, but is not unequivocally ruled out by these data. The Chandra high-energy grating Fe K emission line is consistent with an origin predominantly in Fe I-XVII or so. In a previous LEG observation the line was double-peaked, at ~6.4 keV and ~6.9 keV (H-like Fe). Such a wide range in ionization state of Fe is not ruled out by the HEG data and an earlier ASCA observation, and is suggestive of a complex structure for the line-emitter.
Serlemitsos Peter J.
Yaqoob Tahir
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