Astronomy and Astrophysics – Astrophysics
Scientific paper
2003-11-29
Astrophys.J. 603 (2004) 456-462
Astronomy and Astrophysics
Astrophysics
22 pages, including 5 figures and 2 tables. Accepted for publication in ApJ
Scientific paper
10.1086/381666
We present results from a 50 ks observation of the narrow-line Seyfert 1 galaxy Ark 564 with the Chandra HETGS. The spectra above 2 keV are modeled by a power-law with a photon-index of 2.56+/-0.06. We confirm the presence of the soft excess below about 1.5 keV. If we fit the excess with blackbody model, the best-fit temperature is 0.124 keV. Ark 564 has been reported to show a peculiar emission line-like feature at 1 keV in various observations using lower resolution detectors, and the Chandra grating spectroscopy rules out an origin of blends of several narrow emission lines. We detect an edge-like feature at 0.712 keV in the source rest frame. The preferred interpretation of this feature is combination of the O VII K-edge and a number of L-absorption lines from slightly ionized iron, which suggests a warm absorber with ionization parameter xi~1 and N_H ~ 10^21 cm^-2. These properties are roughly consistent with those of the UV absorber. We also detect narrow absorption lines of O VII, O VIII, Ne IX, Ne X, and Mg XI at the systemic velocity. From these lines, a second warm absorber having log xi ~ 2 and N_H ~ 10^21 cm^-2 is required.
Leighly Karen M.
Marshall Herman L.
Matsumoto Chiho
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