2004ApJ...603..456M

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 a 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 edgelike feature at 0.712 keV in the source rest frame. The preferred interpretation of this feature is a 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 ξ∼1 and N_H∼10²¹/cm2. 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 logξ∼2 and N_H∼10²¹/cm2 is required.