2003ApJ...590L..87W

In this Letter, we report the detection of an extremely strong X-ray emission line in the 940 ks Chandra ACIS-I spectrum of CXOCDFS J033225.3-274219. The source was identified as a type 1 active galactic nucleus at a redshift of z=1.617, with a 2.0-10.0 keV rest-frame X-ray luminosity of ∼10⁴⁴ ergs/s. The emission line was detected at 6.2^+0.2_–0.1keV, with an equivalent width (EW) of 4.4^+3.2_–1.4keV; both quantities refer to the observed frame. In the rest frame, the line is at 16.2^+0.4_–0.3keV with an EW of 11.5^+8.3_–3.7keV. An X-ray emission line at a similar energy (∼17 keV, in the rest frame) in PKS 2149-306 was discovered before using ASCA data. We reject the possibility that the line is due to a statistical or instrumental artifact. The line is most likely due to blueshifted Fe K emission from an relativistic outflow, probably an inner X-ray jet, with velocities of the order of ∼0.6c-0.7c. Other possible explanations are also discussed.