XMM-Newton observation of the NLS1 Galaxy Ark 564: I. Spectral analysis of the time-average spectrum

TL;DR

This study analyzes the X-ray spectrum of the NLS1 galaxy Ark 564 using XMM-Newton data, revealing ionized iron emission, a soft excess likely due to reflection, and high-velocity outflows of highly ionized material.

Contribution

First detailed spectral analysis of Ark 564's X-ray spectrum, identifying ionized iron emission, soft excess components, and high-velocity ionized outflows.

Findings

Detection of ionized iron emission line at 6.7 keV.

Identification of a soft excess consistent with disc reflection.

Evidence for high-velocity outflowing ionized material.

Abstract

We use the data from a recent, 100 ksec XMM-Newton observation of the Narrow Line Seyfert 1 galaxy Ark 564 to obtain its time average, X-ray spectrum. The 3-11 keV spectrum is well fitted by a power-law of slope 2.43. We detect a weak (equivalent width ~80 eV) emission line at ~6.7 keV, which implies emission from ionized iron. There is no compelling evidence for significant broadening of the line.We also detect a possible Doppler shifted absorption line at 8.1 keV. At energies lower than 2 keV, the spectrum is dominated by a smooth soft excess component which can be well fitted either by a two black body components (kT~0.15 and 0.07 keV) or by a black body plus a relativistically blurred photoionized disc reflection model. We detect a broad, shallow flux deficit in the 0.65-0.85 keV band, reminiscent of the iron unresolved transition array (UTA) features. We do not detect neither a strong absorption edge around 0.7 keV nor an emission line around 1 keV. The soft excess emission is consistent with being reflected emission from a geometrically flat disc, with solar abundances, illuminated by an isotropic source. The weakness of the iron line emission can be explained by relativistic blurring. The UTA feature implies the presence of warm material with a column density of 2-5*10^{20} cm^{-2}. If the absorption line at 8.1 keV corresponds to FeXXVI Kalpha, it suggests the presence of a highly ionized absorbing material with N_H > 10^{23} cm^{-2}, outflowing at a high velocity of ~0.17c.