X-ray Emission Research Articles

Multiwavelength coverage of the 2024 periastron passage of PSR B1259–63/LS 2883

ABSTRACT PSR B1259$-$63is a gamma-ray binary system with a 48 ms radio pulsar orbiting around an O9.5Ve star, LS 2883, in a highly eccentric ${\sim} 3.4$ yr long orbit. Close to the periastron the system is detected from radio up to the TeV energies due to the interaction of the stellar wind from LS 2883 and the pulsar’s relativistic outflow. Observations of the last four periastron passages, taken in 2010–2021, demonstrate periastron-to-periastron variability at all wavelengths, probably linked to the state of the Be star’s decretion disc. In this paper, we present the results of our optical, radio and X-ray observational campaigns on PSR B1259$-$63 performed in 2024 accompanied with the analysis of the publicly available GeV Fermi/LAT data. We show that this periastron passage was characterized by the early flaring of X-rays before the periastron passage and GeV emission after the periastron passage, which can be explained by a larger size of the decretion disc as supported by the optical observations. The structure of the GeV flare is also in agreement with the disruption of the large dense disc. The possible X-ray/radio correlation was observed only during the post-periastron rise of X-ray and radio emission.

Adsorbate Configurations in Ni Single-Atom Catalysts during CO_{2} Electrocatalytic Reduction Unveiled by Operando XAS, XES, and Machine Learning.

Nickel and nitrogen co-doped carbon (Ni-N-C) catalysts are attracting attention due to their exceptionally high performance in the electrocatalytic reduction of CO_{2}(CO_{2}RR) to CO. However, the direct experimental insight into the working mechanism of these catalysts is missing, hindering our fundamental understanding and their further improvement. This work sheds light on the nature of adsorbates forming under CO_{2}RR at singly dispersed Ni sites. In particular, operando high energy resolution fluorescence detected x-ray absorption near edge structure (HERFD-XANES) at the Ni K-edge together with valence-to-core x-ray emission spectroscopy (vtc-XES) and x-ray absorption (XAS) at the Ni L_{3}-edge were employed to unveil the structure and electronic properties of the reaction intermediates. These techniques, coupled with unsupervised and supervised machine learning methodologies and density functional theory, enabled a comprehensive characterization of the local atomistic and electronic structure of the working Ni-N-C catalysts. Specifically, we were able to distinguish between the structural and electronic changes of the Ni sites associated with the CO_{2}RR functionality from the effect of radiation-induced damage, providing direct insight into the bond formation between the Ni centers and CO_{2}RR intermediates such as CO adsorbates.

Utilizing High X-ray Energy Photon-In Photon-Out Spectroscopies and X-ray Scattering to Experimentally Assess the Emergence of Electronic and Atomic Structure of ZnS Nanorods.

The key to controlling the fabrication process of transition metal sulfide nanocrystals is to understand the reaction mechanism, especially the coordination of ligands and solvents during their synthesis. We utilize in situ high-energy resolution fluorescence detected X-ray absorption spectroscopy (HERFD-XAS) as well as in situ valence-to-core X-ray emission spectroscopy (vtc-XES) combined with density functional theory (DFT) calculations to identify the formation of a tetrahedral [Zn(OA)4]2+ and an octahedral [Zn(OA)6]2+ complex, and the ligand exchange to a tetrahedral [Zn(SOA)4]2+ complex (OA = oleylamine, OAS = oleylthioamide), during the synthesis of ZnS nanorods in oleylamine. We observe in situ the transition of the electronic structure of [Zn(SOA)4]2+ with a HOMO/LUMO gap of 5.0 eV toward an electronic band gap of 4.3 and 3.8 eV for 1.9 nm large ZnS wurtzite nanospheres and 2 × 7 nm sphalerite nanorods, respectively. Thus, we demonstrate how in situ multimodal X-ray spectroscopy and scattering studies can not only resolve structure, size, and shape during the growth and synthesis of NPs in organic solvents and at high temperature but also give direct information about their electronic structure, which is not readily accessible through other techniques.

The high energy X-ray probe (HEX-P): science overview

To answer NASA’s call for a sensitive X-ray observatory in the 2030s, we present the High Energy X-ray Probe (HEX-P) mission concept. HEX-P is designed to provide the required capabilities to explore current scientific questions and make new discoveries with a broadband X-ray observatory that simultaneously measures sources from 0.2 to 80 keV. HEX-P’s main scientific goals include: 1) understand the growth of supermassive black holes and how they drive galaxy evolution; 2) explore the lower mass populations of white dwarfs, neutron stars, and stellar-mass black holes in the nearby universe; 3) explain the physics of the mysterious corona, the luminous plasma close to the central engine of accreting compact objects that dominates cosmic X-ray emission; and 4) find the sources of the highest energy particles in the Galaxy. These goals motivate a sensitive, broadband X-ray observatory with imaging, spectroscopic, and timing capabilities, ensuring a versatile platform to serve a broad General Observer (GO) and Guest Investigator (GI) community. In this paper, we present an overview of these mission goals, which have been extensively discussed in a collection of more than a dozen papers that are part of this Research Topic volume. The proposed investigations will address key questions in all three science themes highlighted by Astro2020, including their associated priority areas. HEX-P will extend the capabilities of the most sensitive low- and high-energy X-ray satellites currently in orbit and will complement existing and planned high-energy, time-domain, and multi-messenger facilities in the next decade.

Te L-subshell x-ray emission induced by lower energy H2+ ions

The L-shell x-ray emission of tellurium induced by H2+ ions impact is investigated in an energy range of 150–300 keV. The blue shifts of various L-subshell x rays and the enhancement of the relative intensity ratios of Lι, Lβ to Lα x ray are observed and interpreted by the multiple ionization of outer-shell electrons. The new experimental x-ray production cross sections, which almost correspond to those of protons with half of the original energy, are extracted and compared with various theoretical estimations. The correction effects of the united atom approximation and the multiple ionization atomic parameters are compared, and the influence of atomic parameters from different databases on the simulations is discussed. Overall, the ECUSAR-MI calculations using theoretical atomic parameters present the best agreement with the experiment results.

(Invited) In Situ X-Ray Spectroscopy for Clean Energy: Insights into Reactive Intermediates

Transition from fossil fuels requires increased use of solar energy and electrification of chemical industries. To store the excess green electricity from wind and solar generation, batteries and electrolyzers are needed. Green hydrogen can also be produced via artificial photosynthesis where water is split by energy input of sunlight. Hydrogen can be later used in fuel cells. All these applications require new, electrochemically active materials and catalysts. To boost applications in energy storage and conversion, materials with exotic redox states are often desirable. X-ray spectroscopy is an excellent tool for in situ analysis of such energy storage and conversion systems in situ under working conditions.In presentation I will discuss characterization of exotic Mn1+ proposed to play a role in the function of sodium-based Prussian blue analogues (PBA) batteries, a highly sought-out technology for industrial energy storage. Here, we report the detailed electronic structure characterization of uncharged and charged sodium-based manganese hexacyanomanganate anodes via Mn K-edge X-ray absorption spectroscopy (XAS), Kβ nonresonant X-ray emission (XES), and resonant inelastic X-ray scattering (RIXS).For electrochemical and photoelectrochemical water oxidation high oxidation states of IrV, RuV and FeV are needed to activate water and form O-O bond. These species were generated in situ under catalytic conditions and characterized by hard X-ray XAS. Active catalyst such as [Ru(H3-Tpy)(Qc)Cl] was assembled into MIL-142 metal organic framework to produce device prototype for artificial photosynthesis. It delivered high photocurrent in the photo-electrocatalytic water splitting at pH=1 and unassisted photocatalytic H2 evolution under visible light with Pt as the co-catalyst. The high activity of this new system enables hydrogen gas capture from an easy-to-manufacture, scaled-up prototype utilizing MOF deposited on FTO glass as a photoanode.

(Invited) Electrocatalytic Activity and Structural Insights of Cu, Fe and N-Doped Mesoporous Carbon for the Oxygen Reduction Reaction

For widespread applications of polymer electrolyte fuel cells, non-PGM electrocatalysts with high oxygen reduction reaction (ORR) activity and product selectivity to H2O need to be developed. Metal, nitrogen-doped carbon (M–N–C, M = Fe, Co, Cu, etc.) electrocatalysts have been intensively studied as non-PGM based electrocatalysts in acidic media for the ORR because they show relatively high ORR activity in the non-PGM-based electrocatalysts. Recently, heterometallic doping into nitrogen-doped carbon, which is known as dual-metal atom catalysts, can show the cooperative effect on the ORR activity and product selectivity. We have also developed such heterometallic non-PGM electrocatalysts of Cu, Fe, N-doped carbon nanotubes for the ORR in acidic media, inspired by the active site of a natural ORR catalyst of cytochrome c oxidase [1]. The co-doping of Cu and Fe in carbon nanotubes improves the ORR activity and product selectivity toward H2O via four-electron transfer. However, its ORR activity is relatively low (a turnover frequency of 0.40 e– site–1 s–1 at +0.80 V vs. RHE) and the structure of the active site remains unclear.We report the synthesis, activity and structural insight of a Cu, Fe, N-doped mesoporous carbon, (Cu,Fe)–N–mesoC, electrocatalyst for the ORR in acidic media. (Cu,Fe)–N–mesoC was prepared in pyrolysis from the composite of an iron complex of a 1,12-diazatriphenylene ligand [2], a multinuclear copper complex of 1,2,4-triazole [3] and mesoporous carbon. (Cu,Fe)–N–mesoC shows a turnover frequency of 1.35 e– site–1 s–1 at +0.80 V vs. RHE and a low hydrogen peroxide yield (< 5%). X-ray absorption and emission spectroscopy of (Cu,Fe)–N–mesoC was performed to understand the structure of the active site.References.[1] M. Kato, N. Fujibayashi, D. Abe, N. Matsubara, S. Yasuda, I. Yagi, ACS Catal., 11, 2356-2365 (2021).[2] K. Matsumoto et al., Chem. Eur. J., 28, e20210345 (2022).[3] M. Kato et al., ACS Appl. Energy Mater., 1, 2358-2364 (2018).

Conventional and High-Entropy Spinels As Oxygen Evolution Electrocatalysts (ECs) for Implementation in Low-Temperature Electrolyzers (ELs): Synthesis, Physicochemical Studies and Electrochemical Characterization

One of the cornerstones of the “hydrogen economy” is the widespread implementation of “green hydrogen” to a variety of applications spanning from transportation to industry and stationary power. The most straightforward approach to obtain such “green hydrogen” in large amounts at acceptable costs is to use the energy obtained from renewable sources to split water in an electrolyzer (EL) [1]. Low-temperature ELs running on either alkaline or neutral water are highly promising technologies to obtain “green hydrogen” since their electrode configurations can operate effectively even without the use of electrocatalysts (ECs) based on critical raw materials (CRMs) such as platinum-group metals (PGMs). To ensure that the conversion efficiency of such ELs is high enough for practical applications, it is mandatory that the overpotential in the oxygen evolution reaction (OER) is minimized by the implementation of a suitable EC at the anode.This report describes both conventional and high-entropy spinels as promising OER ECs for implementation at the anode of low-temperature ELs. The spinels include a variety of metal cations (e.g., Ni, Cr, Mn, Fe, Zn, Co and Cu) and are typically obtained by a combination of steps carried out either/both at low T (e.g., hydrothermal processes) and at high T (e.g., calcination). The chemical composition of the spinels is determined both in the bulk and on the surface implementing analytical techniques such as inductively-coupled plasma atomic emission spectroscopy (ICP-AES), X-ray fluorescence and near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS). The morphology of the spinels is elucidated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM); the porosimetric features are studied by nitrogen physisorption measurements. The structure of the spinels is probed by vibrational spectroscopies (e.g., confocal micro-Raman) and wide-angle powder X-ray diffraction. The OER kinetics and reaction mechanism of the spinels are quantified by means of cyclic voltammetry with the thin-film rotating ring-disk electrode (CV-TF-RRDE). Finally, the OER durability of the most promising candidates is evaluated “ex-situ” after the implementation of suitable accelerated ageing protocols. The results of the physicochemical and electrochemical characterizations are correlated with the synthetic parameters, yielding information on the most promising approaches to obtain spinel-based OER ECs able to bestow to low-T ELs a performance and durability beyond the state of the art.

PIXE, SEM and RAMAN analysis of pictorial materials from the VIII century crypt of San Salvatore, Brescia (Italy)

The complex of Santa Giulia of Brescia (Italy) is a great and extensively studied architectural and archaeological site, of which the church of San Salvatore is an emblematic monument. This study, conducted in the crypt of the church, implements what was published from non-destructive particle induced x-ray emission (PIXE) examination of the painting materials with structural and compositional analyses by Scanning Electron Microscopy and Raman spectroscopy. These analyses produced new and decisive data for a correct identification of the pictorial palette. We also added a photographic documentation in a few bands of the electromagnetic spectrum. The review of all data and their complementarity has allowed a more sound insight into the pictorial techniques used for the crypt’s decoration. This work integrates the archaeological studies conducted on the crypt and, together with them and in comparison with data from coeval monuments, confirms in the church of San Salvatore the use of products and techniques typical of the Longobard Period.

(Invited) Experimental Insights into the Local Chemical Environment of Sulfur Atoms and Their Relevance in Photoelectrochemical Water Splitting Devices Made of Cu(In,Ga)(S,Se)2 and Other Things

It is the purpose of this presentation to demonstrate how the unique capabilities of novel x-ray spectroscopy methods (in particular element-specific soft x-ray emission spectroscopy, XES) can be employed to derive important insights into PEC and other solar devices from the viewpoint of sulfur. Of course, other elements will also play a role, as will delocalized valence and conduction bands, but sulfur is unique and deserves to be celebrated.The presentation will include results from lab-based x-ray and UV photoelectron spectroscopy, inverse photoelectron spectroscopy, and x-ray-excited Auger electron spectroscopy, complemented by XES and soft x-ray absorption spectroscopy using high-brilliance synchrotron radiation. A particularly powerful approach is their resonant combination, Resonant Inelastic soft X-ray Scattering (RIXS), best displayed in a “RIXS map”.In the presentation, we will discuss the impact of sulfur on the electronic level alignment at surfaces and interfaces, and how to go about learning more about local chemical bonding (hybridization) in the vicinity of sulfur atoms, using a large variety of compounds as examples – sulfides, sulfates, chalcopyrites, ... The presentation will thus also include a bit of a discussion of cutting-edge instrumentation recently developed for studying buried layers and materials in in situ and operando environments, such as the novel X-SPEC beamline and its unique endstations at the KIT Light Source in Karlsruhe, Germany.

(Invited) Hard X-Ray Core Shell Spectroscopy Studies of Battery Materials

Understanding the charge compensation mechanisms during electrochemical cycling of battery materials is of both fundamental and applied interest. X-ray Absorption Fine Structure (XAFS), an element specific probe of the projected, unoccupied density of states as well as the local and medium-range structure around the probed photoabsorbing atom, has been a workhorse technique that sheds light on the atomic and electronic structure of the metal ions. However, the rising edge at the metal K-edge — the energy of which is used in assigning oxidation state — also depends on other factors such as the nature of the ligand, covalency, coordination number, and metal spin-state. We have recently show that by coupling XAFS with Resonant X-ray Emission Spectroscopy (RXES), questions concerning metal oxidation state and site symmetry can be addressed, even in highly covalent systems [1]. In this talk, we will highlight the application of these hard X-ray spectroscopy methods to understand fundamental structure-function relationships of materials and systems relevant to lithium-ion batteries. The first topic of the talk will address the redox mechanisms and migration tendencies in an earth-abundant Li1.3Mn0.5Fe0.2O 2 cathode material (see figure below). In the second topic, we will examine the evolution of the electronic structure of nickel and dopant ions (cobalt) in a nickel-rich material.[1] Redox Mechanisms and Migration Tendencies in Earth-Abundant 0.7Li2MnO3·0.3LiFeO2 Cathodes: Coupling Spin-Resolved X-ray Absorption Near Edge and X-ray Absorption Fine Structure Spectroscopies, C.Y. Kwok, S. Mallick, C. J. Pollock, A. Gutierrez, M. Dixit, J. R. Croy, and M. Balasubramanian, Chemistry of Materials 2024 36 (1), 300-312 Figure 1

Quantitative Chemical State Analysis of Silicon-Based Anodes for Lithium Ion Battery Using X-Ray Emission Spectroscopy

The advancement of lithium-ion batteries for electric vehicles has prompted the utilization of diverse materials, including substances like amorphous and sulphated materials, which may lack inherent stability. Consequently, employing various analytical techniques, spectral analysis, and in-operando cell testing becomes imperative for their characterization. We assess the potential of X-ray Emission Spectroscopy (XES) to integrate chemical state and quantitative analysis, capitalizing on its bulk analysis capabilities with large analytical area and deep analytical depth.Silicon-based anodes offer high theoretical capacities and hold promise for lithium-ion batteries in electric vehicles. However, their practical application is hindered by poor cycling performance and mechanical failure attributed to significant volume changes during lithiation. Understanding the formation of amorphous and crystalline lithium silicon alloy phases, crucial for capacity degradation analysis, underscores the importance of quantifying the x value in the Li x Si phase. SiO emerges as a compelling anode material with potential to enhance energy capacity and mitigate degradation. Demonstrating this property involves the complex conversion of SiO to amorphous Si and lithium silicates during charging.While electrochemical reaction mechanisms and structural changes in silicon-based anodes have been explored using various techniques such as 7Li and 29Si solid-state NMR, Si K XAS, and Si-L2,3 soft X-ray emission spectroscopy, accurately quantifying reacted components remains challenging.In this study, Si Kβ X-ray emission spectroscopy (XES) is employed to quantify the composition of lithium-silicon alloys and lithium silicates during charging and discharging processes. The Si Kβ spectrum evolves with the reaction progression, and linear combination fitting (LCF) proves instrumental in estimating material quantities based on the reaction formula. The quantitative results of the XES analysis are shown and the accuracy, validity and findings are discussed.

Evaluation of Electronic and Crystal Structures of Li-Rich Layered Oxide Cathode Using Combinations of Exes, XPS, and PDF Analyses

Lithium-rich layered oxides (LLOs) have attracted attention as high-capacity cathode materials for lithium-ion secondary batteries. Its unique charge-compensation mechanism and structure changes during delithiation and lithiation yield a large capacity. LLOs reversibly extract and insert ~1 mol of Li (> 250 mAh/g) per Li1+x Me 1 − x O2 (Me=Ni, Co, Mn) notation. In contrast, conventional layered oxides such as LiCoO2 reversibly extract and insert ~0.6 mol (~160 mAh/g), which is limited by the irreversible change of the host structure by the excessive Li extraction. However, such a large amount of delithiation in LLOs still induces various structural changes. Although various structure analyses, including conventional XRD, have revealed the structural changes of LLOs accompanying charging and discharging, the inherently disordered structure of LLOs requires a more elaborate experimental approach to elucidate the relationship between the structural changes and electrode properties. Because conventional XRD only provides structure information of the well-ordered crystalline phase, the structure evolution of LLOs and their charging/discharging mechanisms should be elucidated to reveal such disordered structures. Pair distribution function (PDF) analysis, which is an advanced XRD technique using X-ray total scattering, enables quantitative observations of the short-, medium-, and long-range orders with high spatial resolutions in real space even from highly disordered structures simultaneously. In addition, spectroscopic analyses have revealed the unique charge compensation mechanisms associated with the high capacity of LLOs. In LLOs, the contribution of O anions is a key factor for the reversible high capacity. Another consideration is the valence bands of both O and Me from simultaneous observations of constituent elements, since the O 2p and Me 3d orbitals are hybridized. Soft X-ray emission spectroscopy (SXES) is a useful technique to observe the electronic structure of multiple elements simultaneously. Among them, electron-induced X-ray emission spectroscopy (EXES) is an accessible technique using laboratory X-ray or electron beam sources for excitation. In this study, we performed EXES and PDF analyses along with X-ray photoelectron spectroscopy (XPS) on the same states of samples for the LLO cathode, 0.4Li2MnO3−0.6LiNi0.5Mn0.5O2, to reveal the relation between the charge compensation mechanism and changes in the crystal structure. The PDF analysis suggested that charging caused Me cations to migrate to the octahedral and tetrahedral sites in the Li layer. EXES independently observes the energy distribution of each orbital, revealing their specific roles in the charge compensation accompanying electrochemical charging and discharging. EXES with the aid of XPS revealed that the charge was compensated by Ni, Mn, and O. The contribution from each element depended on the charging/discharging state. The changes in the electronic/crystalline structures that yield the unique charge-compensation mechanism and the large capacity of the LLO electrode will be discussed.

Spin-State Analysis for a Fourteen-Membered Macrocyclic Fe Complex for Oxygen Reduction

For the broad application of polymer electrolyte fuel cells (PEFCs), the development of non-precious-metal (NPM) catalysts for oxygen reduction is extremely important. To date, many NPM catalyst have been synthesized by pyrolyzing Fe-, N-, and C-containing precursors, but they suffer from the low density and uncertain chemical structure of their active sites. On the contrary, our research group has been studying a 14-membered macrocyclic Fe complex, which was inspired by the FeNx sites embed in graphene sheets.In this study, a fourteen-membered macrocyclic Fe complex was loaded on a carbon support and then heat-treated, and found to be quite active as a non-precious metal oxygen reduction catalyst. The improvement is attributed to a high turnover frequency rather than the number of active sites. To fully understand the mechanism for the improved catalytic activity, the spin-state of the catalysts was evaluated by X-ray emission spectroscopy, and the results were discussed in comparison to a simulation study based on the density functional theory (DFT). The obtained results suggest that the Fe-based active sites are working in a middle-spin state. Figure 1

Utilizing Advanced Spectroscopy Techniques to Investigate Mn-Ligand Bonding Environments in Disordered Rocksalt Oxyfluorides

Li-rich disordered rock-salt oxyfluorides (DRS) stand out as a promising class of cathode materials due to their exceptional electrochemical performance [1-3]. The substitution of oxygen (O) with fluorine (F) within DRS compounds has demonstrated a significant enhancement in reversible discharge capacity, making them highly desirable candidates for next-generation high-energy Li-ion batteries with enhanced capacity. Despite considerable research into the structural and electrochemical characteristics of these materials, the metal-fluorine (M-F) bonding in DRS oxyfluorides has received limited attention [4,5]. To address this gap in knowledge, we synthesized oxyfluorides based on manganese (Mn) with a composition of Li2MO2F. Employing advanced spectroscopy techniques, we sought to unravel the intricate details of Mn-F bonding in DRS materials. Specifically, we utilized Kβ X-ray emission spectroscopy (XES) to examine the Mn bonding environment and performed fluorine Resonant Inelastic X-ray Scattering (RIXS) measurements to gain insights into the F bonding perspective. Kβ XES has therefore been established as a probe of both metal and ligand properties and RIXS of F enables a direct investigation of Mn-F bonding dynamics by identifying alterations in emission features corresponding to various excitation energies in the F XAS pre-edge region upon charging [6-8]. Furthermore, Kβ XES analysis offers valuable information on the oxidation states and covalency trends of Mn-ligand interactions comparing with the end-member Mn oxides and fluorides.

Laboratory-Based X-Ray Emission Spectroscopy (XES) for Determination of Oxidation State and Ligand Species

Identification of oxidation state and ligand species is often challenging, requiring arduous preparation and destructive analytical techniques which inhibit rapid analyses. Advancements in laboratory-based X-ray emission spectrometers (XES) are addressing this issue, facilitating consistent access to element-specific bulk chemical analysis of oxidation state and ligand speciation in users’ own labs. Intended to simplify and expand access to this powerful technique for both new and existing members of the XAS community, everyday analysis is a game-changer which enables researchers to control their experiment like never before. Synchrotron-like data quality is achievable within minutes even on trace elements (few hundred PPM). Utilizing a Rowland-circle geometry, easyXAFS spectrometers support a broad energy range (2-25 keV) capable of XES analysis of over 50 elements ranging from phosphorus through the actinides. Herein we discuss the benefits of XES for determination of oxidation state and ligand speciation highlighting previous and ongoing research in electrocatalysis, cathode coatings, battery charge/discharge operando measurements. Figure 1

Multi-Observatory Research of Young Stellar Energetic Flares (MORYSEF): X-Ray-flare-related Phenomena and Multi-epoch Behavior

The most powerful stellar flares driven by magnetic energy occur during the early pre-main-sequence (PMS) phase. The Orion Nebula represents the nearest region populated by young stars, showing the greatest number of flares accessible to a single pointing of Chandra. This study is part of a multi-observatory project to explore stellar surface magnetic fields (with the Hobby–Eberly Telescope Habitable-zone Planet Finder, HET-HPF), particle ejections (with the Very Long Baseline Array, VLBA), and disk ionization (with the Atacama Large Millimeter/submillimeter Array, ALMA) immediately following the detection of PMS superflares with Chandra. In 2023 December, we successfully conducted such a multi-telescope campaign. Additionally, by analyzing Chandra data from 2003, 2012, and 2016, we examine the multi-epoch behavior of PMS X-ray emission related to PMS magnetic cyclic activity and ubiquitous versus sample-confined megaflaring. Our findings are as follows. (1) We report detailed stellar quiescent and flare X-ray properties for numerous HET/ALMA/VLBA targets, facilitating ongoing multiwavelength analyses. (2) For numerous moderately energetic flares, we report correlations (or lack thereof) between flare energies and stellar mass/size (presence/absence of disks) for the first time. The former is attributed to the correlation between convection-driven dynamo and stellar volume, while the latter suggests the operation of solar-type flare mechanisms in PMS stars. (3) We find that most PMS stars exhibit minor long-term baseline variations, indicating the absence of intrinsic magnetic dynamo cycles or observational mitigation of cycles by saturated PMS X-rays. (4) We conclude that X-ray megaflares are ubiquitous phenomena in PMS stars, which suggests that all protoplanetary disks and nascent planets are subject to violent high-energy emission and particle irradiation events.

Modeling the X-Ray Emission of the Boomerang Nebula and Implication for Its Potential Ultrahigh-energy Gamma-Ray Emission

The Boomerang Nebula is a bright radio and X-ray pulsar wind nebula (PWN) powered by an energetic pulsar, PSR J2229+6114. It is spatially coincident with one of the brightest ultrahigh-energy (UHE; ≥100 TeV) gamma-ray sources, LHAASO J2226+6057. While X-ray observations have provided radial profiles for both the intensity and photon index of the nebula, previous theoretical studies have not reached an agreement on their physical interpretation, which also leads to different anticipation of the UHE emission from the nebula. In this work, we model its X-ray emission with a dynamical evolution model of PWN, considering both convective and diffusive transport of electrons. On the premise of fitting the X-ray intensity and photon index profiles, we find that the magnetic field within the Boomerang Nebula is weak (∼10 μG in the core region and diminishing to 1 μG at the periphery), which therefore implies a significant contribution to the UHE gamma-ray emission by the inverse Compton (IC) radiation of injected electron/positron pairs. Depending on the particle transport mechanism, the UHE gamma-ray flux contributed by the Boomerang Nebula via the IC radiation may constitute about 10%–50% of the flux of LHAASO J2226+6057 at 100 TeV and up to 30% at 500 TeV. Finally, we compare our results with previous studies and discuss potential hadronic UHE emission from the PWN. In our modeling, most of the spindown luminosity of the pulsar may be transformed into thermal particles or relativistic protons.

A Self-consistent Model of Shock-heated Plasma in Nonequilibrium States for Direct Parameter Constraints from X-Ray Observations

X-ray observations of shock-heated plasmas, such as those found in supernova remnants (SNRs), often exhibit features of temperature and ionization nonequilibrium. For accurate interpretation of these observations, proper calculations of the equilibration processes are essential. Here, we present a self-consistent model of thermal X-ray emission from shock-heated plasmas that accounts for both temperature and ionization nonequilibrium conditions. For a given pair of shock velocity and initial electron-to-ion temperature ratio, the temporal evolution of the temperature and ionization state of each element was calculated by simultaneously solving the relaxation processes of temperature and ionization. The resulting thermal X-ray spectrum was synthesized by combining our model with the AtomDB spectral code. Comparison between our model and the nei model, a constant-temperature nonequilibrium ionization model available in the XSPEC software package, reveals a 30% underestimation of the ionization timescale in the nei model. We implemented our model in XSPEC to directly constrain the shock wave’s properties, such as the shock velocity and collisionless electron heating efficiency, from the thermal X-ray emission from postshock plasmas. We applied this model to archival Chandra data of the SNR N132D, providing a constraint on the shock velocity of ∼800 km s−1, in agreement with previous optical studies.

Sulfur Speciation in Li-S Batteries Determined by Operando Laboratory X-ray Emission Spectroscopy.

In this work, operando sulfur X-ray emission measurements on a Li-S battery cathode were performed using a laboratory setup as an alternative to more common synchrotron radiation based absorption studies. Photoexcitation by an X-ray tube was used. Valence-to-core Kβ X-ray emission spectra were recorded with a wavelength dispersive crystal spectrometer in von Hamos geometry, providing excellent energy resolution and good detection efficiency. The setup was used to record ex situ S Kβ emission spectra from S cathodes from the Li-S battery and also under operando conditions. Average S oxidation state within the battery cathode during battery cycling was determined from the shape of the Kβ emission spectra. A more detailed S species characterization was performed by fitting a linear combination of previously measured laboratory synthesized standards to the measured spectra. Relative amounts of different S species in the cathode were determined during the cycling of the Li-S battery. The main advantage of X-ray emission spectroscopy is that it can be performed on concentrated samples with S loading comparable to a real battery. The approach shows great promise for routine laboratory analysis of electrochemical processes in Li-S batteries and other sulfur-based systems under operando conditions.