Searching for the warm-hot intergalactic medium using XMM-Newton high-resolution X-ray spectra

The problem of missing baryons in the local universe remains an open question. One propose alternative is that at low redshift missing baryons are in the form of the Warm Hot Intergalactic Medium (WHIM). In order to test this idea, we present a detailed analysis of X-ray high-resolution spectra of six extragalactic sources, Mrk 421, 1ES 1028+511, 1ES 1553+113, H2356-309, PKS 0558-504 and PG 1116+215, obtained with the XMM-Newton Reflection Grating Spectrometer to search for signals of WHIM and/or circumgalactic medium (CGM) X-ray absorbing gas. We fit the X-ray absorption with the IONeq model, allowing us to take into account the presence of X-ray spectral features due to the multiphase component of the local ISM. An additional IONeq component is included to model the WHIM absorption, instead of the traditional Gaussian absorption line modeling. We found no statistical improvement in the fits when including such component in any of the sources, concluding that we can safely reject a successful detection of WHIM absorbers towards these lines of sights. Our simulation shows that the presence of the multiphase ISM absorption features prevents detection of low-redshift WHIM absorption features in the 17 A spectral region for moderate exposures using high-resolution spectra.Comment: 12 pages, 7 figure

Chandra high-resolution spectra of 4U 1630-47: the disappearance of the wind

We present the analysis of six Chandra X-ray high-resolution observations of the black hole low-mass X-ray binary 4U 1630-47 taken during its 2012–2013 outburst. Fe XXVI K α, K β, Fe XXV K α, K β, and Ca XX K α blueshifted absorption lines were identified in the first four observations, which correspond to soft accretion states. The remaining observations, associated to intermediate and possibly hard accretion states, do not show significant absorption features down to equivalent width of 1 eV for both Fe XXVI and Fe XXV. We inferred wind launching radii between 1.2 − 2.0 (1012 cm/n) × 1011 cm and column densities N(H) > 1023 cm−2. In the first four observations, we found that thermal pressure is likely to be the dominant launching mechanism for the wind, although such conclusions depend on the assumed density. We used the spectral energy distributions obtained from our continuum modelling to compute thermal stability curves for all observations using the XSTAR photoionization code. We found that the absence of lines in the transitional state cannot be attributed to an evolution of the plasma caused by thermal instabilities derived from the change in the continuum spectrum. In contrast, the disappearance of the wind could indicate an acceleration of the flow or that the plasma has been exhausted during the soft state

Sulphur X-ray absorption in the local ISM

We present a study S K-edge using high-resolution HETGS Chandra spectra of 36 low-mass X-ray binaries. For each source, we have estimated column densities for S I, S II, S III, S XIV, S XV, and S XVI ionic species, which trace the neutral, warm, and hot phases of the Galactic interstellar medium. We also estimated column densities for a sample of interstellar dust analogues. We measured their distribution as a function of Galactic latitude, longitude, and distances to the sources. While the cold-warm column densities tend to decrease with the Galactic latitude, we found no correlation with distances or Galactic longitude. This is the first detailed analysis of the sulphur K-edge absorption due to ISM using high-resolution X-ray spectra

Simultaneous detection of an intrinsic absorber and a compact jet emission in the X-ray binary IGR J17091-3624 during a hard accretion state

We present a detailed analysis of three XMM-Newton observations of the black hole low-mass X-ray binary IGR~J17091-3624 taken during its 2016 outburst. Radio observations obtained with the Australia Telescope Compact Array (ATCA) indicate the presence of a compact jet during all observations. From the best X-ray data fit results we concluded that the observations were taken during a transition from a hard accretion state to a hard-intermediate accretion state. For Observations 1 and 2 a local absorber can be identified in the EPIC-pn spectra but not in the RGS spectra, preventing us from distinguishing between absorption local to the source and that from the hot ISM component. For Observation 3, on the other hand, we have identified an intrinsic ionized static absorber in both EPIC-pn and RGS spectra. The absorber, observed simultaneously with a compact jet emission, is characterized by an ionization parameter of 1.96< log({\xi}) <2.05 and traced mainly by Ne X, Mg XII, Si XIII and Fe XVIII.Comment: 13 pages, 10 figure

Sulfur X-ray absorption in the local ISM

We present a study S K-edge using high-resolution HETGS {\it Chandra} spectra of 36 low-mas X-ray binaries. For each source, we have estimated column densities for {\rm S}~{\sc i}, {\rm S}~{\sc ii}, {\rm S}~{\sc iii}, {\rm S}~{\sc xiv}, {\rm S}~{\sc xv} and {\rm S}~{\sc xvi} ionic species, which trace the neutral, warm and hot phases of the Galactic interstellar medium. We also estimated column densities for a sample of interstellar dust analogs. We measured their distribution as a function of Galactic latitude, longitude, and distances to the sources. While the cold-warm column densities tend to decrease with the Galactic latitude, we found no correlation with distances or Galactic longitude. This is the first detailed analysis of the sulfur K-edge absorption due to ISM using high-resolution X-ray spectra.Comment: 8 pages, 6 figure

A Comprehensive X-ray Absorption Model for Atomic Oxygen

An 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 Kedge, 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 shake-up 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