X-ray emission from thin plasmas. Collisional ionization for atoms and ions of H to Zn

Every observation of astrophysical objects involving a spectrum requires atomic data for the interpretation of line fluxes, line ratios and ionization state of the emitting plasma. One of the processes which determines it is collisional ionization. In this study an update of the direct ionization (DI) and excitation-autoionization (EA) processes is discussed for the H to Zn-like isoelectronic sequences. In the last years new laboratory measurements and theoretical calculations of ionization cross sections have become available. We provide an extension and update of previous published reviews in the literature. We include the most recent experimental measurements and fit the cross sections of all individual shells of all ions from H to Zn. These data are described using an extension of Younger's and Mewe's formula, suitable for integration over a Maxwellian velocity distribution to derive the subshell ionization rate coefficients. These ionization rate coefficients are incorporated in the high-resolution plasma code and spectral fitting tool SPEX V3.0.Comment: Accepted for publication in A&A, 22 pages, 18 figure

Tunneling of massive and charged particles from noncommutative Reissner-Nordstr\"{o}m black hole

Massive charged and uncharged particles tunneling from commutative Reissner-Nordstrom black hole horizon has been studied with details in literature. Here, by adopting the coherent state picture of spacetime noncommutativity, we study tunneling of massive and charged particles from a noncommutative inspired Reissner-Nordstrom black hole horizon. We show that Hawking radiation in this case is not purely thermal and there are correlations between emitted modes. These correlations may provide a solution to the information loss problem. We also study thermodynamics of noncommutative horizon in this setup.Comment: 10 pages, 2 figure

Magnesium and silicon in interstellar dust: an X-ray overview

The dense Galactic environment is a large reservoir of interstellar dust. Therefore, this region represents a perfect laboratory to study the properties of the cosmic dust grains. X-rays are the most direct way to detect the interaction of light with dust present in these dense environments. The interaction between the radiation and the interstellar matter imprints specific absorption features in the X-ray spectrum. We study them with the aim of defining the chemical composition, the crystallinity and structure of the dust grains which populate the inner regions of the Galaxy. We investigate the magnesium and the silicon K-edges detected in the Chandra/HETG spectra of eight bright X-ray binaries, distributed in the neighbourhood of the Galactic centre. We model the two spectral features using accurate extinction cross sections of silicates, that we have measured at the synchrotron facility Soleil, France. Near the Galactic centre magnesium and silicon show abundances similar to the solar ones and they are highly depleted from the gas phase ($\delta_{\rm{Mg}}>0.90$ and $\delta_{\rm{Si}}>0.96$). We find that amorphous olivine with a composition of $\rm MgFeSiO_{4}$ is the most representative compound along all lines of sight according to our fits. The contribution of Mg-rich silicates and quartz is low (less than $10\%$). On average we observe a percentage of crystalline dust equal to $11\%$. For the extragalactic source LMC X-1, we find a preference for forsterite, a magnesium-rich olivine. Along this line of sight we also observe an underabundance of silicon $A_{\rm Si}/A_{\rm LMC} = 0.5\pm0.2$.Comment: 16 pages, 7 figures, recommended for publication in Astronomy and Astrophysic

Interstellar oxygen along the line of sight of Cygnus X-2

Interstellar dust permeates our Galaxy and plays an important role in many physical processes in the diffuse and dense regions of the interstellar medium. High-resolution X-ray spectroscopy, coupled with modelling based on laboratory dust measurements, provides a unique probe to investigate the interstellar dust properties along our line of sight towards Galactic X-ray sources. Here, we focus on the oxygen content of the interstellar medium through its absorption features in the X-ray spectra. To model the dust features, we perform a laboratory experiment using the electron microscope facility located at the University of Cadiz in Spain, where we acquire new laboratory data in the oxygen K-edge. We study 18 dust samples of silicates and oxides with different chemical compositions. The laboratory measurements are adopted for our astronomical data analysis. We carry out a case study on the X-ray spectrum of the bright low-mass X-ray binary Cygnus X-2, observed by XMM-Newton. We determine different temperature phases of the ISM, and parameterize oxygen in both gas (neutral and ionised) and dust form. We find Solar abundances of oxygen along the line of sight towards the source. Due to both the relatively low depletion of oxygen into dust form and the shape of the oxygen cross section profiles, it is challenging to determine the precise chemistry of interstellar dust. However, silicates provide an acceptable fit. Finally, we discuss the systematic discrepancies in the atomic (gaseous phase) data of the oxygen edge spectral region using different X-ray atomic databases, and also consider future prospects for studying the ISM with the Arcus concept mission.Comment: Accepted for publication in A&A, 15 pages, 11 figure

Entropic force approach to noncommutative Schwarzschild black holes signals a failure of current physical ideas

Recently, a new perspective of gravitational-thermodynamic duality as an entropic force arising from alterations in the information connected to the positions of material bodies is found. In this paper, we generalize some aspects of this model in the presence of noncommutative Schwarzschild black hole by applying the method of coordinate coherent states describing smeared structures. We implement two different distributions: (a) Gaussian and (b) Lorentzian. Both mass distributions prepare the similar quantitative aspects for the entropic force. Our study shows, the entropic force on the smallest fundamental unit of a holographic screen with radius $r_0$ vanishes. As a result, black hole remnants are unconditionally inert even gravitational interactions do not exist therein. So, a distinction between gravitational and inertial mass in the size of black hole remnant is observed, i.e. the failure of the principle of equivalence. In addition, if one considers the screen radius to be less than the radius of the smallest holographic surface at the Planckian regime, then one encounters some unusual dynamical features leading to gravitational repulsive force and negative energy. On the other hand, the significant distinction between the two distributions is conceived to occur around $r_0$, and that is worth of mentioning: at this regime either our analysis is not the proper one, or non-extensive statistics should be employed.Comment: 15 pages, 2 figures, new references added, minor revision, Title changed, to appear in EPJ Plu

Accretion, ejection and reprocessing in supermassive black holes

This is a White Paper in support of the mission concept of the Large Observatory for X-ray Timing (LOFT), proposed as a medium-sized ESA mission. We discuss the potential of LOFT for the study of active galactic nuclei. For a summary, we refer to the paper.Comment: White Paper in Support of the Mission Concept of the Large Observatory for X-ray Timin

Science with hot astrophysical plasmas

We present some recent highlights and prospects for the study of hot astrophysical plasmas. Hot plasmas can be studied primarily through their X-ray emission and absorption. Most astrophysical objects, from solar system objects to the largest scale structures of the Universe, contain hot gas. In general we can distinguish collisionally ionised gas and photoionised gas. We introduce several examples of both classes and show where the frontiers of this research in astrophysics can be found. We put this also in the context of the current and future generation of X-ray spectroscopy satellites. The data coming from these missions challenge the models that we have for the calculation of the X-ray spectra

Space Telescope and Optical Reverberation Mapping project. XI. Disk-wind characteristics and contributions to the very broad emission lines of NGC 5548

Funding: Support for HST program number GO-13330 was provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. We thank NSF (1816537, 1910687), NASA (17-ATP17-0141, 19-ATP19-0188), and STScI (HST-AR-15018, HST-AR-14556). MC acknowledges support from NASA through STScI grant HST-AR-14556.001-Aand NASA grant 19-ATP19-0188, and also support from National Science Foundation through grant AST-1910687.M.D. and G.F. and F. G. acknowledge support from the NSF (AST-1816537), NASA (ATP 17-0141), and STScI (HST-AR-13914, HST-AR-15018), and the Huffaker Scholarship. M.M. is supported by the Netherlands Organization for Scientific Research (NWO) through the Innovational Research Incentives Scheme Vidi grant 639.042.525. J.M.G. gratefully acknowledges support from NASA under the ADAP award 80NSSC17K0126. MV gratefully acknowledges support from the Independent Research Fund Denmark via grant number DFF 8021-00130.In 2014 the NGC 5548 Space Telescope and Optical Reverberation Mapping campaign discovered a two-month anomaly when variations in the absorption and emission lines decorrelated from continuum variations. During this time the soft X-ray part of the intrinsic spectrum had been strongly absorbed by a line-of-sight (LOS) obscurer, which was interpreted as the upper part of a disk wind. Our first paper showed that changes in the LOS obscurer produces the decorrelation between the absorption lines and the continuum. A second study showed that the base of the wind shields the broad emission-line region (BLR), leading to the emission-line decorrelation. In that study, we proposed the wind is normally transparent with no effect on the spectrum. Changes in the wind properties alter its shielding and affect the spectral energy distribution (SED) striking the BLR, producing the observed decorrelations. In this work we investigate the impact of a translucent wind on the emission lines. We simulate the obscuration using XMM-Newton, NuSTAR, and Hubble Space Telescope observations to determine the physical characteristics of the wind. We find that a translucent wind can contribute a part of the He ii and Fe Kα emission. It has a modest optical depth to electron scattering, which explains the fainter far-side emission in the observed velocity-delay maps. The wind produces the very broad base seen in the UV emission lines and may also be present in the Fe Kα line. Our results highlight the importance of accounting for the effects of such winds in the analysis of the physics of the central engine.Publisher PDFPeer reviewe