Hard X-ray Sources Research Articles

Towards in Operando XAS Investigation of CO2 Electrolysis in Solid Oxide Cells: Synchrotron Studies of La0.3Ca0.7Fe0.7Cr0.3O3-δ Perovskites

Solid oxide cells (SOCs) are poised to provide a significant contribution to the emerging field of green technology. SOCs could form the basis for a closed loop, sustainable energy system in which fuel cells generate power efficiently and any waste products are converted back into fuel or useful products.Early solid oxide fuel cell (SOFC) systems utilized ceramic-metal composites, such as Ni-YSZ, as the fuel electrodes. Ni metal provides electronic conduction while YSZ plays the role of oxygen anion conductor. This requires the catalyst target (e.g., H2) to come into contact with both Ni and YSZ, forming a so-called triple phase boundary.Cermet systems perform well but are typically unstable under oxidizing conditions and are susceptible to passivating phenomena, such as sulfur poisoning. Since then, mixed ionic and electronic conductors (MIECs) have been developed, where a single material such as a perovskite replaces both cermet components. The gas-MIEC interface acts as a double phase boundary, theoretically providing electrochemical reaction sites on the entire surface of the electrode. This makes them less susceptible to poisoning by impurities, and the oxide composition can be tailored to improve stability in reducing or oxidizing environments. SOFCs based on mixed-conducting catalysts have shown marked performance increases over room-temperature fuel cells in ORR catalysis, often with an order of magnitude advantage in current response. Further work led to MIEC compositions being used at SOFC fuel electrodes, and more recently, as active catalysts for the carbon dioxide reduction (CO2RR) reaction in electrolysis cells (SOECs).Our research group recently demonstrated that the perovskite material, La0.3Ca0.7Fe0.7Cr0.3O3-δ (LCFCr), shows excellent stability and activity during the OER and ORR. This single composition is also highly active for the CO2RR, opening the door for reversible and symmetrical SOC devices (RSOFCs) that promise to greatly reduce device complexity. This should ease the difficulty of scaling up these technologies for industrial applications. While we have observed performance gains in both SOC modes of operation using LCFCr, we sought to better understand the underlying mechanism of catalysis in CO2 electrolysis. This has led us to begin a thorough investigation of LCFCr-based reversible SOFCs using synchrotron x-ray absorption spectroscopy (XAS), culminating with in operando studies, where CO2 electrolysis can be tracked as it happens in fully operational electrolysis cells. Harsh operating conditions have made in situ or in operando SOC studies more challenging than those for RT cells, which also share the barriers of access to electrode surfaces and the attenuation effect of feedstocks on incident energy used for spectroscopy.This presentation will introduce our initial efforts in synchrotron XAS studies of the as-synthesized LCFCr material, which was prepared by combustion synthesis of precursor metal nitrates. Synchrotron energy provided by the Canadian Light Source (CLS) was used to study powder samples of this composition; experiments were carried out at both hard (SXRMB) and soft (SGM) x-ray sources at the CLS. Preliminary experiments consisted of ex situ XAS testing of samples heat treated using conditions similar to those encountered in operation (800 °C in air or CO2). When compared to spectra of as-synthesized compositions, this provides a conventional “before and after” comparison and has demonstrated that overall changes in oxidation state and coordination environment could be observed. In situ testing was also carried out at SXRMB on La0.3Ca0.7Fe0.7Cr0.3O3-δ powder samples. Samples were placed in a “six-shot” apparatus that provided a versatile test bed for semi-realistic conditions. In these studies, materials were heated in air to 800 °C, while XANES spectra (Fe K-edge) were collected simultaneously. This process was repeated as the gas was changed to CO2, and then upon cooling. These transitionary XAS measurements allowed us to observe both structure and valence state of the material responding in real time. The results showed changes in the pre-edge feature and edge intensity that we have attributed to a change in local vacancy concentration around Fe metal centers. At each stable set of conditions, full EXAFS spectra were collected for all four metals; initial analysis suggests that chromium undergoes redox changes while the iron valence state remains largely unchanged. Together, this set of experiments is allowing us to assemble a dynamic picture of the chemical and structural state of the catalyst during operation.This study underscores the value of in situ and in operando investigation of SOC catalysts compared to traditional ex situ analysis. Insights into efficient SOC electrolysis of CO2 could give us the ability to reduce carbon emissions. It is both urgent and vital that the underlying mechanisms are understood more completely.

Hard X-Ray Phase-Contrast Laboratory Microscope Based on Three-Block Fresnel Zone Plate Interferometer

A device based on a three-block Fresnel zone plate interferometer is proposed for hard X-ray phase-contrast imaging. The device combines a low requirement for the coherence of the initial radiation (the interferometer operates in the amplitude division mode) with an optical magnification of the image. A numerical simulation of the image formation is carried out, taking into account the limited source-interferometer distance, the size and spectral width of the X-ray source. The calculations show that the proposed set-up can be used as a phase-contrast microscope using laboratory hard X-ray sources.

Imaging of hard x-ray radiations using Gafchromic™ dosimetry film in Damavand tokamak

In the present study, a series of experiments were performed to study collisions of runaway electrons in the Damavand tokamak by imaging hard x-ray radiations, as one of the secondary effects of these electrons, using radiochromic films. For these experiments, GAFCHROMIC™EBT2 dosimetry films were selected due to their high resolution imaging capability. These instruments were installed in two strip and screen structures for one- and two-dimensional imaging in high-dose areas of the Damavand tokamak, and after irradiation on the device, the recorded data were extracted using a flatbed scanner. The results showed that in runaway discharges of the Damavand tokamak, if active plasma position control system is off, predominant collision of the runaway electrons column occurs with outer wall of the vacuum chamber. Also, the recorded images indicated that dimensions of temporary sources of hard x-rays in the Damavand tokamak are about 10 cm × 10 cm. Two-dimensional imaging in these experiments showed that toroidal field coils are exposed to significant hard x-ray radiations, making the use of radiation-sensitive diagnostic systems in this area questionable. The results obtained from measurements also indicated that the highest radiation dose in the Damavand tokamak is in the limiter region and reaches up to 300 mSv shot−1.

Search for high-energy neutrino emission from hard X-ray AGN with IceCube

The IceCube Neutrino Observatory has detected high-energy astrophysical neutrinos in the TeV-PeV range. These neutrinos have an isotropic distribution on the sky, and therefore, likely originate from extragalactic sources. Active Galactic Nuclei form a class of astronomical objects which are promising neutrino source candidates given their high electromagnetic luminosity and potential ability to accelerate cosmic rays up to energies greater than 1016 eV. Interactions of these cosmic rays within the AGN environment are expected to produce both neutrinos and pionic gamma rays. Some hadronic models of AGN emission suggest that such gamma rays can in turn interact with the dense photon fields of AGN and cascade down to hard X-rays and MeV gamma rays. We present an update on the IceCube stacking analysis searching for high-energy neutrinos from hard X-ray sources sampled from the Swift-BAT AGN Spectroscopic Survey.

Investigating the true nature of three hard X-ray sources

ABSTRACT Many of the new high energy sources discovered both by INTEGRAL/IBIS and Swift/BAT have been characterized thanks to extensive, multiband follow-up campaigns, but there are still objects whose nature remains to be asserted. In this paper, we investigate the true nature of three high energy sources, IGR J12134−6015, IGR J16058−7253, and Swift J2037.2+4151, employing multiwavelength data from the near-infrared to the X-rays. Through Gaia and ESO-VLT measurements and through Swift/XRT X-ray spectral analysis, we re-evaluate the classification for IGR J12134−6015, arguing that the source is a Galactic object and in particular a cataclysmic variable. We were able to confirm, thanks toNuclear Spectroscopic Telescope Array(NuSTAR) observations, that the hard X-ray emission detected by INTEGRAL/IBIS and Swift/BAT from IGR J16058−7253 is coming from two Seyfert 2 galaxies which are both counterparts for this source. Through optical and X-ray spectral analysis of SwiftJ2037.2+4151 we find that this source is likely part of the rare and peculiar class of symbiotic X-ray binaries and displays flux and spectral variability as well as interesting spectral features, such as a blending of several emission lines around the iron line complex.

Fully-staggered-array bulk Re-Ba-Cu-O short-period undulator: large-scale 3D electromagnetic modelling and design optimization using A-V and H-formulation methods

The development of a new hard x-ray beamline I-TOMCAT equipped with a 1 m long short-period bulk high-temperature superconductor undulator (BHTSU) has been scheduled for the upgrade of the Swiss Light Source at the Paul Scherrer Institute. The very hard x-ray source generated by the BHTSU will increase the brilliance at the beamline by over one order of magnitude in comparison to other state-of-the-art undulator technologies and allow experiments to be carried out with photon energies in excess of 60 keV. One of the key challenges for designing a 1 m long (100 periods) BHTSU is the large-scale simulation of the magnetization currents inside 200 staggered-array bulk superconductors. A feasible approach to simplify the electromagnetic model is to retain five periods from both ends of the 1 m long BHTSU, reducing the number of degrees of freedom to the scale of millions. In this paper, the theory of the recently-proposed 2D A -V formulation-based backward computation method is extended to calculate the critical state magnetization currents in the ten-period staggered-array BHTSU in 3D. The simulation results of the magnetization currents and the associated undulator field along the electron beam axis are compared with the well-known 3D H -formulation and the highly efficient 3D H -ϕ formulation method, all methods showing excellent agreement with each other as well as with experimental results. The mixed H -ϕ formulation avoids computing the eddy currents in the air subdomain and is significantly faster than the full H -formulation method, but is slower in comparison to the A -V formulation-based backward computation. Finally, the fastest and the most efficient A -V formulation, implemented in ANSYS 2020R1 Academic, is adopted to optimize the integrals of the undulator field along the electron beam axis by optimizing the sizes of the end bulks.

A Gemini–NIFS view of the merger remnant NGC 34

ABSTRACT The merger remnant NGC 34 is a local luminous infrared galaxy (LIRG) hosting a nuclear starburst and a hard X-ray source associated with a putative, obscured Seyfert 2 nucleus. In this work, we use adaptive optics assisted near-infrared (NIR) integral field unit observations of this galaxy to map the distribution and kinematics of the ionized and molecular gas in its inner $\mathrm{1.2\, kpc \times 1.2\, kpc}$, with a spatial resolution of 70 pc. The molecular and ionized gas kinematics is consistent with a disc with projected major axis along a mean PA = −9${_{.}^{\circ}}$2 ± 0${_{.}^{\circ}}$9. Our main findings are that NGC 34 hosts an AGN and that the nuclear starburst is distributed in a circumnuclear star formation ring with inner and outer radii of ≈ 60 and 180 pc, respectively, as revealed by maps of the $\mathrm{[Fe\, {\small {II}}] / Pa\,\beta }$ and H2/Br γ emission-line ratios, and corroborated by PCA tomography analysis. The spatially resolved NIR diagnostic diagram of NGC 34 also identifies a circumnuclear structure dominated by processes related to the stellar radiation field and a nuclear region where $[\rm Fe\, {\small {II}}]$ and H2 emissions are enhanced relative to the hydrogen recombination lines. We estimate that the nuclear X-ray source can account for the central H2 enhancement and conclude that $[\rm Fe\, {\small {II}}]$ and H2 emissions are due to a combination of photoionization by young stars, excitation by X-rays produced by the AGN and shocks. These emission lines show nuclear, broad, blueshifted components that can be interpreted as nuclear outflows driven by the AGN.

Infrared Emission Properties of Active Galactic Nuclei from Swift-BAT Hard X-Ray Survey

The Swift/Burst Alert Telescope (BAT) 105-month survey detected 1632 hard X-ray sources in the 14–195 keV band, which includes 1105 active galactic nuclei (AGNs) that are unbiased against Compton-thin obscuration. We use a series of two-color diagrams to analyze the near, mid (MIR), and far-infrared properties of the Swift/BAT AGNs, based on data from the Two Micron All Sky Survey, the Wide Field Infrared Survey Explorer and the AKARI satellite. The two-color diagrams imply that a power-law spectrum of can be used to describe the 1.25–22 μm spectra of most of the Swift/BAT AGNs and that, for some Swift/BAT AGNs, the power-law spectrum can extend to 90 μm. Of the Swift/BAT AGNs, type-1 AGNs and QSOs have similar MIR spectral indexes (α) on average. Type-2 AGNs have redder MIR colors than type-1 sources on average. For 50% of type-2 Swift/BAT AGNs, their near-infrared emissions are dominated by thermal emission of the stars in host galaxies. For 83% of type-1 Swift/BAT AGNs, their near-infrared emissions may be dominated by multi-temperature thermal emissions from an optically thick accretion disk around the central black holes. The spectral index of blazars is smaller than that of other Swift/BAT AGNs, which indicates that blazars/FSRQ have flatter 4–22 μm spectra compared to other Swift/BAT AGNs on average.

Ultrafast structural dynamics using time-resolved x-ray diffraction driven by relativistic laser pulses* *Project supported by the National Key R&D Program of China (Grant No. 2017YFA0403301), Science Challenge Project (Grant No. TZ2018005), the National Natural Science Foundation of China (Grant Nos. 11991073, 11721404, 11805266, 11905289, and 61975229), and Key Program of Chinese Academy of Sciences (Grant Nos. XDA25030400 and XDB17030500).

Based on a femtosecond laser plasma-induced hard x-ray source with a high laser pulse energy (> 100 mJ) at 10 Hz repetition rate, we present a time-resolved x-ray diffraction system on an ultrafast time scale. The laser intensity is at relativistic regime (2 × 1019 W/cm2), which is essential for effectively generating Kα source in high-Z metal material. The produced copper Kα radiation yield reaches to 2.5 × 108 photons/sr/shot. The multilayer mirrors are optimized for monochromatizating and two-dimensional beam shaping of Kα emission. Our experiment exhibits its ability of monitoring the transient structural changes in a thin film SrCoO2.5 crystal. It is demonstrated that this facility is a powerful tool to perform dynamic studies on samples and adaptable to the specific needs for different particular applications with high flexibility.

Thicket high Z wavelength-scale structured target: advantages and limitations for laser-driven hard x-ray source and phase contrast imaging

The hard x-ray copper K α source formed by the interaction of a high intensity laser pulse with flat and thicket sub-micron structured copper targets is thoroughly characterized. It is shown that the flux of quanta can be increased up to several times using the structured target instead of the flat one. The maximal conversion efficiency into K α reaches 1.4 × 10−4 corresponding to >109 photons with a high contrast ratio over the bremsstrahlung radiation at the peak intensity ∼1018 W cm−2. The efficient use of the thicket target at higher intensity (2 × 1018 W cm−2) is limited by temporal contrast of the laser pulse and the few-fold lowered damage threshold of the modified target. Measurements of the x-ray source size revealed that the lateral coherence is similar both for the flat and thicket target. The estimated source size of ∼15 μm makes it suitable for the x-ray phase contrast imaging with reasonable geometry and short time object exposure. A simple concept of the image acquisition correction is proposed in order to account for the x-ray source lateral shifts, which is based on measurements in each shot instead of long exposure. Image post-processing allowed us to enhance source lateral coherence and retrieve phase contrast effects when the x-ray source shifts exceed its size.

Using Chandra Localizations and Gaia Distances and Proper Motions to Classify Hard X-Ray Sources Discovered by INTEGRAL

Abstract Here, we report on X-ray observations of ten 17–60 keV sources discovered by the International Gamma-Ray Astrophysics Laboratory satellite. The primary new information is sub-arcsecond positions obtained by the Chandra X-ray Observatory. In six cases (IGR J17040-4305, IGR J18017-3542, IGR J18112-2641, IGR J18434-0508, IGR J19504+3318, and IGR J20084+3221), a unique Chandra counterpart is identified with a high degree of certainty, and for five of these sources (all but J19504), Gaia distances or proper motions indicate that they are Galactic sources. For four of these, the most likely classifications are that the sources are magnetic cataclysmic variables (CVs). J20084 could be either a magnetic CV or a high-mass X-ray binary. We classify the sixth source (J19504) as a likely active galactic nucleus (AGN). In addition, we find likely Chandra counterparts to IGR J18010-3045 and IGR J19577+3339, and the latter is a bright radio source and probable AGN. The other two sources, IGR J12529-6351 and IGR J18013-3222, do not have likely Chandra counterparts, indicating that they are transient, highly variable, or highly absorbed.

The INTEGRAL view on black hole X-ray binaries

INTEGRAL is an ESA mission in fundamental astrophysics that was launched in October 2002. It has been in orbit for over 18 years, during which it has been observing the high-energy sky with a set of instruments specifically designed to probe the emission from hard X-ray and soft γ-ray sources. This paper is devoted to the subject of black hole binaries, which are among the most important sources that populate the high-energy sky. We present a review of the scientific literature based on INTEGRAL data, which has significantly advanced our knowledge in the field of relativistic astrophysics. We briefly summarise the state-of-the-art of the study of black hole binaries, with a particular focus on the topics closer to the INTEGRAL science. We then give an overview of the results obtained by INTEGRAL and by other observatories on a number of sources of importance in the field. Finally, we review the main results obtained over the past 18 years on all the black hole binaries that INTEGRAL has observed. We conclude with a summary of the main contributions of INTEGRAL to the field, and on the future perspectives.

The nuclear environment of NGC 2442: a Compton-thick low-luminosity AGN

ABSTRACT The detailed study of nuclear regions of galaxies is important because it can help understanding the active galactic nucleus (AGN) feedback mechanisms, the connections between the nuclei and their host galaxies, and ultimately the galaxy formation processes. We present the analysis of an optical data cube of the central region of the galaxy NGC 2442, obtained with the integral field unit (IFU) of the Gemini Multi-Object Spectrograph (GMOS). We also performed a multiwavelength analysis, with Chandra data, XMM–Newton and NuSTAR spectra, and Hubble Space Telescope (HST) images. The analysis revealed that the nuclear emission is consistent with a Low Ionization Nuclear Emission-line Region (LINER) associated with a highly obscured compact hard X-ray source, indicating a Compton-thick AGN. The HST image in the F658N filter (H α) reveals an arched structure corresponding to the walls of the ionization cone of the AGN. The gas kinematic pattern and the high gas velocity dispersion values in the same region of the ionization cone suggest an outflow emission. The stellar archaeology results indicate the presence of only old stellar populations (∼ 10 Gyr), with high metallicity (z = 0.02 and 0.05), and the absence of recent star formation in the central region of NGC 2442, which is possibly a consequence of the AGN feedback, associated with the detected outflow, shutting off star formation. NGC 2442 is a late-type galaxy similar to the Milky Way, and comparisons show that the main difference between them is the presence of a low-luminosity AGN.

Online data analysis system of the INTEGRAL telescope

Context. During more than 17 years of operation in space, the INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL) telescope has accumulated a large data set that contains records of hard X-ray and soft γ-ray astronomical sources. These data can be reused in the context of multi-wavelength or multi-messenger studies of astronomical sources and have to be preserved on long timescales. Aims. We present a scientific validation of an interactive online INTEGRAL data analysis system for multi-wavelength studies of hard X-ray and soft γ-ray sources. Methods. The online data analysis system generates publication-quality high-level data products: sky images, spectra, and light curves in response to user queries that define analysis parameters such as source position, time and energy interval, and binning. The data products can be requested via a web browser interface or via an application programming interface that is available as a Python package. The products for the Imager on Board the INTEGRAL Satellite/INTEGRAL Soft Gamma-Ray Imager instrument of INTEGRAL are generated using the offline science analysis (OSA) software, which is provided by the instrument teams and is conventionally used to analyse INTEGRAL data. The analysis workflow is organised to preserve and reuse various intermediate analysis products, ensuring that frequently requested results are available without delay. The platform is implemented in a Docker cluster that allows operation of the software in a controlled virtual environment and can be deployed in any compatible infrastructure. The scientific results produced by the open data analysis (ODA) are identical to those produced by OSA because ODA simply provides a platform to retrieve the OSA results online while leveraging a provenance-indexed database of precomputed (cached) results to optimise and reuse the result. Results. We report the functionalities and performance of the online data analysis system by reproducing the benchmark INTEGRAL results on different types of sources, including bright steady and transient Galactic sources, and bright and weak variable extra-galactic sources. We compare the results obtained with the online data analysis system with previously published results on these sources. We also discuss limitations of the online analysis system. Conclusions. We consider the INTEGRAL online data analysis as a demonstration of a more general web-based ‘data analysis as a service’ approach that provides a promising solution for the preservation and maintenance of data analysis tools of astronomical telescopes on (multi)decade long timescales and facilitates combining data in multi-wavelength and multi-messenger studies of astronomical sources.

Hard X-Ray Emission Associated with White Dwarfs. IV. Signs of Accretion from Substellar Companions

Abstract With an effective temperature of ≃200,000 K, KPD 0005+5106 is one of the hottest white dwarfs (WDs). ROSAT unexpectedly detected “hard” (∼1 keV) X-rays from this apparently single WD. We have obtained Chandra observations that confirm the spatial coincidence of this hard X-ray source with KPD 0005+5106. We have also obtained XMM-Newton observations of KPD 0005+5106, as well as PG 1159−035 and WD 0121−756, which are also apparently single and whose hard X-rays were detected by ROSAT at 3σ–4σ levels. The XMM-Newton spectra of the three WDs show remarkably similar shapes that can be fitted by models including a blackbody component for the stellar photospheric emission, a thermal plasma emission component, and a power-law component. Their X-ray luminosities in the 0.6–3.0 keV band range from 4 × 1029 to 4 × 1030 erg s−1. The XMM-Newton EPIC-pn soft-band (0.3–0.5 keV) light curve of KPD 0005+5106 is essentially constant, but the hard-band (0.6–3.0 keV) light curve shows periodic variations. An analysis of the generalized Lomb–Scargle periodograms for the XMM-Newton and Chandra hard-band light curves finds a convincing modulation (false-alarm probability of 0.41%) with a period of 4.7 ± 0.3 hr. Assuming that this period corresponds to a binary orbital period, the Roche radii of three viable types of companion have been calculated: M9V star, T brown dwarf, and Jupiter-like planet. Only the planet has a size larger than its Roche radius, although the M9V star and T brown dwarf may be heated by the WD and inflate past the Roche radius. Thus, all three types of companion may be donors to fuel accretion-powered hard X-ray emission.

Standard variable short period microwave-plasma undulator

Microwave-plasma undulator (MPU), as a standard short-period length undulator, is a desirable source of hard X-ray with continuous wide spectrum. In this article, the electron wiggling motion under the effect of transverse electric mode, propagating in cold plasma-filled waveguide, is investigated. The deflection parameter and period length of MPU in counter-propagating and co-propagating modes are calculated. Advantages of MPU over conventional and microwave undulators are investigated. It is shown that MPUs generate higher photon flux with overlapping harmonics compared to conventional standard undulators and cover wider energy range of synchrotron radiation. A rectangular MPU with period length of 2.98 mm and deflection parameter of 2.23 and a circular MPU with period length of 2.99 mm and deflection parameter of 2.23 are introduced. Also, a short variable period MPU, with the period length varying from 2.62 mm to 4.12 mm, and a helical MPU is introduced.

Production of warm dense water in the laboratory using intense ion beams at FAIR: Application to planetary physics

This paper presents two-dimensional hydrodynamic simulations of implosion of a water sample, which is enclosed in a cylindrical shell of tungsten that is driven by an intense uranium beam. The considered beam parameters match the characteristics of the beam which will be delivered by the heavy ion synchrotron, SIS100, at the Facility for Antiprotons and Ion Research (FAIR). An experimental scheme based on this concept, which is named LAPLAS, is an important part of the high energy density physics research program at FAIR. The simulations show that the LAPLAS implosion leads to a low-entropy compression of water, which generates core conditions of water-rich planets. The importance of this work is underscored by the fact that more than 30% of the discovered extrasolar planets are Neptune-like water-rich planets. To be able to construct a reliable physical model of the formation and evolution of these planets, it is important to have correct understanding of the equation of state of the exotic states of water that exist in the planetary interior. It is thus expected that the knowledge obtained from the LAPLAS experiments will be a very valuable contribution to the field of planetary physics. We show that x-ray radiographic imaging using a high-intensity laser-driven hard x-ray source would be a suitable diagnostic capable of delivering high-resolution images of the hydrodynamic evolution.

Multiwavelength observations of the Galactic X-ray binaries IGR J20155+3827 and Swift J1713.4−4219

ABSTRACT In recent years, thanks to the continuous surveys performed by INTEGRAL and Swift satellites, our knowledge of the hard X-ray/soft gamma-ray sky has greatly improved. As a result it is now populated with about 2000 sources, both Galactic and extra-galactic, mainly discovered by IBIS and BAT instruments. Many different follow-up campaigns have been successfully performed by using a multiwavelength approach, shedding light on the nature of a number of these new hard X-ray sources. However, a fraction are still of an unidentified nature. This is mainly due to the lack of lower energy observations, which usually deliver a better constrained position for the sources, and the unavailability of the key observational properties, needed to obtain a proper physical characterization. Here, we report on the classification of two poorly studied Galactic X-ray transients IGR J20155+3827 and Swift J1713.4−4219, for which the combination of new and/or archival X-ray and optical/NIR (near-infrared) observations have allowed us to pinpoint their nature. In particular, thanks to XMM–Newton archival data together with new optical spectroscopic and archival optical/NIR photometric observations, we have been able to classify IGR J20155+3827 as a distant HMXB (high-mass X-ray binaries). The new INTEGRAL and Swift data collected during the 2019 X-ray outburst of Swift J1713.4−4219, in combination with the archival optical/NIR observations, suggest an LMXB (low-mass X-ray binaries) classification for this source.

Illumination of the accretion disk in black hole binaries: An extended jet as the primary source of hard X-rays

Context.The models that seek to explain the reflection spectrum in black hole binaries usually invoke a point-like primary source of hard X-rays. This source illuminates the accretion disk and gives rise to the discrete (lines) and continuum-reflected components.Aims.The main goal of this work is to investigate whether the extended, mildly relativistic jet that is present in black hole binaries in the hard and hard-intermediate states is the hard X-ray source that illuminates the accretion disk.Methods.We use a Monte Carlo code that simulates the process of inverse Compton scattering in a mildly relativistic jet rather than in a “corona” of some sort. Blackbody photons from the thin accretion disk are injected at the base of the jet and interact with the energetic electrons that move outward with a bulk velocity that is a significant fraction of the speed of light.Results.Despite the fact that the jet moves away from the disk at a mildly relativistic speed, we find that approximately 15−20% of the input soft photons are scattered, after Comptonization, back toward the accretion disk. The vast majority of the Comptonized, back-scattered photons escape very close to the black hole (h ≲ 6 rg, wherergis the gravitational radius), but a non-negligible amount escape at a wide range of heights. At high heights,h ∼ 500−2000 rg, the distribution falls off rapidly. The high-height cutoff strongly depends on the width of the jet at its base and is almost insensitive to the optical depth. The disk illumination spectrum is softer than the direct jet spectrum of the radiation that escapes in directions that do not encounter the disk.Conclusions.We conclude that an extended jet is an excellent candidate source of hard photons in reflection models.

Validation of a laser driven plasma X-ray microfocus source for high resolution radiography imaging.

Hard X-ray radiation with high brightness and high fluxes is nowadays available on the fourth generation of synchrotrons and X-FELs, but the large size and complexity of these sources makes its use difficult for widespread applications. New table top X-ray sources driven by ultrashort high power lasers offer a compelling route to expand the availability of hard X-ray sources. They can be used for advanced imaging techniques, due to its small source size and spatial coherence. We present in this paper the validation of a compact laser-driven X-ray microfocus source for high-resolution radiography imaging. This novel device was built at the Laser Laboratory for Acceleration and Applications (L2A2) at the University of Santiago de Compostela. This paper describes the laser-plasma X-ray source with improved stability and characterize some of its properties. We demonstrate the high-contrast and resolution of the images obtained with this source by using masks with well known geometries, and detailed analysis by using the modulation transfer function. Finally, we discuss the properties of this source in comparison to other compact microfocus X-ray sources.