ChandraLETGS observation of the variable NLS1 galaxy Ark 564

Abstract

We present an analysis of the 100 ks X-ray spectrum of the narrow-line Seyfert 1 Galaxy Ark 564, taken with the Low Energy Transmission Grating Spectrometer (LETGS) on board Chandra. Using χ 2 statistics, several continuum models of the time-averaged spectrum of this object are compared, obtaining a semi-empirical solution for the description of the intrinsic emission continuum and a physical solution for the intrinsic absorption of the system. We find that the 0.1−10 keV spectrum can be well described by a power law plus two thermal components that account for the soft step. We are also able to detect and measure several narrow, unresolved absorption lines arising from highly ionized species of C, N, O, and Fe. The material seems to have a velocity consistent with the systemic velocity of the galaxy. This piece of evidence, in addition to the very low observed column density of N H ∼ 10 20 cm −2 , is in good agreement with the scenario of a transverse biconical outflow with a gas density of n 3 × 10 12 cm −3 at distances beyond the broad-line region r 10 lt-days, but a dust torus origin cannot be ruled out.

Probing the photoionised outflow in the NLS1 Arakelian 564: AnXMM-Newtonview

“…This is assumed to be a cold neutral absorber (kT ∼ 0.5 eV) and clearly fits the O I Galactic oxygen line at 23.5 Å in the RGS spectrum. This was also identified earlier by Ramírez (2013) and Smith et al (2008). However, the HOT model also predicts absorption around 17.47 Å, which corresponds to neutral iron.…”

“…Generally the features we report are similar to other works. We obtain similar column density and ionisation parameters to Ramírez (2013), who observed Ark 564 using Chandra LETGS. The analysis of the line at observed wavelength of 19 Å suggests this is from Phase 2, and we get a slightly higher ionisation parameter of Log ξ = 1.34 to their Log ξ = 1.1, but very similar column density and line width.…”

K-shell photoionization ofO+andO2+ions: Experiment and theory

“…K-shell photoabsorption of oxygen and its ions is often responsible for prominent features in the interstellar medium (ISM) absorption spectra in the 500-600-eV photon energy range. Indeed oxygen K-shell absorption lines have been observed towards both low-mass x-ray binaries [1][2][3][4][5] and active nucleus of Seyfert galaxies [6][7][8].…”

X-Ray Outflows of Active Galactic Nuclei Warm Absorbers: A 900 ks Chandra Simulated Spectrum

“…Following a series of papers related with the computations of K lines of Fe (Palmeri et al (2002(Palmeri et al ( , 2003a), and K-shell photoabsorption of O ions (Ramírez and Bautista (2002); García et al (2005García et al ( , 2011 atomic data (energies, cross sections, lifetimes), Palmeri et al (2008)) discuss in detail the reliability and accuracy of some sets of these data (medium-Z elements), currently observed in the X-ray spectrum of active galactic nuclei (AGNs, e.g., NGC 3783 Kaspi et al (2002); Ramírez et al (2005); Ramírez (2011), MR 2251−178 , APM 08279+5255 Ramírez (2008), Ark 564 Ramírez (2013)), in the form of K-absorption lines of H-and Helike Ne,Mg,Si,S, possibly Ar and Ca, and also from lower and medium ionization stages of Si and S (e.g., for MCG-6-30-15 and IRAS 13349+2438) (Holczer et al (2007)), with the aim of improving the atomic database of the xstar modelling code.…”