We present the analysis of the first Nuclear Spectroscopic Telescope Array observations (∼220 ks), simultaneous with the last Suzaku observations (∼50 ks), of the active galactic nucleus of the bright Seyfert 1 galaxy Mrk509. The time-averaged spectrum in the 1-79 keV X-ray band is dominated by a power-law continuum (Γ ∼ 1.8-1.9), a strong soft excess around 1 keV, and signatures of X-ray reflection in the form of Fe K emission (∼6.4 keV), an Fe K absorption edge (∼7.1 keV), and a Compton hump due to electron scattering (∼20-30 keV). We show that these data can be described by two very different prescriptions for the soft excess: a warm (kT ∼ 0.5-1 keV) and optically thick (τ ∼ 10-20) Comptonizing corona or a relativistically blurred ionized reflection spectrum from the inner regions of the accretion disk. While these two scenarios cannot be distinguished based on their fit statistics, we argue that the parameters required by the warm corona model are physically incompatible with the conditions of standard coronae. Detailed photoionization calculations show that even in the most favorable conditions, the warm corona should produce strong absorption in the observed spectrum. On the other hand, while the relativistic reflection model provides a satisfactory description of the data, it also requires extreme parameters, such as maximum black hole spin, a very low and compact hot corona, and a very high density for the inner accretion disk. Deeper observations of this source are thus necessary to confirm the presence of relativistic reflection and further understand the nature of its soft excess.

7An analytical formula is developed to represent accurately the photoabsorption cross section of O I for all energies of interest in X-ray spectral modeling.In the vicinity of the K edge, a Rydberg series expression is used to fit R-matrix results, including important orbital relaxation effects, that accurately predict the absorption oscillator strengths below threshold and merge consistently and continuously to the above-threshold cross section. Further minor adjustments are made to the threshold energies in order to reliably align the atomic Rydberg resonances after consideration of both experimental and observed line positions. At energies far below or above the K-edge region, the formulation is based on both outer-and inner-shell direct photoionization, including significant shakeup and shake-off processes that result in photoionization-excitation and double photoionization contributions to the total cross section. The ultimate purpose for developing a definitive model for oxygen absorption is to resolve standing discrepancies between the astronomically observed and laboratory measured line positions, and between the inferred atomic and molecular oxygen abundances in the interstellar medium from xstar and spex spectral models.Subject headings: X-rays: ISM -ISM: atoms -atomic processes -line: formation -8 line: profiles 9 Atomic photoionization, an important astrophysical process, has been studied for 11 more than a century since the seminal understanding of its energetics by Einstein (1905) 12 and the first calculations of quantum mechanical cross sections (Bates 1939). Over the 13 years, a plethora of experimental and theoretical investigations have managed an excellent 14 grasp of its physics (Fano & Cooper 1968; Starace 1982), together with a remarkable 15 quantitative description of the valence-shell photoionization of atoms and atomic ions 16 (Opacity Project Team 1995, 1997). However, the quantitative model of inner-shell 17 photoabsorption is less sound due to a variety of relaxation processes, namely Auger and 18 X-ray emission, that must be taken into account in order to achieve acceptable accuracy, 19 especially in the near-threshold region. 20 Inner-shell photoabsorption of metals with nuclear charge 7 ≤ Z ≤ 28 is directly 21 accessible to modern X-ray observatories such as Chandra and XMM-Newton, and, hence, 22 is of much interest in astronomy. Particularly prominent in the photoabsorption of the 23 interstellar medium (ISM) are the K-shell features (lines and edges) of atomic oxygen, 24 which is the most abundant metal and is critically important in the energetic and chemical 25 evolution of the Universe (Stasińska et al. 2012). At present, though, the unsatisfactory 26 quantitative understanding of oxygen inner-shell photoabsorption is such that there exists 27 various sets of cross sections, each one leading to different conclusions regarding the 28 ionization and atomic-to-molecular fractions in the ISM along various Galactic lines of 29 sight. 30 The first inner-shell photoabsorption cross se...

We present an X-ray absorption model for the interstellar medium, to be referred to as ISMabs, that takes into account both neutral and ionized species of cosmically abundant elements, and includes the most accurate atomic data available. Using high-resolution spectra from eight X-ray binaries obtained with the Chandra High Energy Transmission Grating Spectrometer, we proceed to benchmark the atomic data in the model particularly in the neon K-edge region. Compared with previous photoabsorption models, which solely rely on neutral species, the inclusion of ions leads to improved spectral fits. Fit parameters comprise the column densities of abundant contributors that allow direct estimates of the ionization states. ISMabs is provided in the appropriate format to be implemented in widely used X-ray spectral fitting packages such as XSPEC, ISIS and SHERPA.

We have developed a new X-ray absorption model, called IONeq, which computes the optical depth τ (E) simultaneously for ions of all abundant elements, assuming ionization equilibrium and taking into account turbulent broadening. We use this model to analyze the interstellar medium (ISM) absorption features in the Milky Way for a sample of 18 galactic (LMXBs) and 42 extragalactic sources (mainly Blazars). The absorbing ISM was modeled as a combination of three components/phases -neutral (T 1 × 10 4 K), warm (T ∼ 5 × 10 4 K) and hot (T ∼ 2 × 10 6 K). We found that the spatial distribution of both, neutral and warm components, are difficult to describe using smooth profiles due to nonuniform distribution of the column densities over the sky. For the hot phase we used a combination of a flattened disk and a halo, finding comparable column densities for both spatial components, in the order of ∼ 6−7×10 18 cm −2 , although this conclusion depends on the adopted parametrization. If the halo component has sub-solar abundance Z, then the column density has be scaled up by a factor Z Z . The vertically integrated column densities of the disk components suggests the following mass fractions for these three ISM phases in the Galactic disk: neutral ∼ 89%, warm ∼ 8% and hot ∼ 3% components, respectively. The constraints on the radial distribution of the halo component of the hot component are weak.

We present detailed analyses of oxygen K absorption in the interstellar medium (ISM) using four high-resolution Chandra spectra towards the X-ray low-mass binary XTE J1817-330. The 11-25Å broadband is described with a simple absorption model that takes into account the pileup effect and results in an estimate of the hydrogen column density. The oxygen K-edge region (21-25Å)is fitted with the physical warmabs model, which is based on a photoionization model grid generated with the xstar code with the most up-to-date atomic database. This approach allows a benchmark of the atomic data which involves wavelength shifts of both the K lines and photoionization cross sections in order to fit the observed spectra accurately. As a result we obtain: a column density of N H = 1.38 ± 0.01 × 10 21 cm −2 ; ionization parameter of log ξ = −2.70 ± 0.023; oxygen abundance of A O = 0.689 +0.015 −0.010 ; and ionization fractions of O I/O = 0.911, O II/O = 0.077, and O III/O = 0.012 that are in good agreement with previous studies. Since the oxygen abundance in warmabs is given relative to the solar standard of Grevesse & Sauval (1998), a rescaling with the revision by Asplund et al. (2009) yields A O = 0.952 +0.020 −0.013 , a value close to solar that reinforces the new standard. We identify several atomic absorption lines-Kα, Kβ, and Kγ in O I and O II; and Kα in O III, O VI, and O VII-last two probably residing in the neighborhood of the source rather than in the ISM. This is the first firm detection of oxygen K resonances with principal quantum numbers n > 2 associated to ISM cold absorption.