X-ray Pulses Research Articles

Spectral analysis of Ultra-Luminous X-ray pulsars with models of X-ray pulsars

Abstract A fraction of the Ultra Luminous X-ray (ULX) sources are known to be accreting neutron stars as they show coherent X-ray pulsations with pulse periods ranging from ∼1 − 30 seconds. While initially thought to host intermediate-mass black holes, ULXs have since been recognized as a diverse class of objects, including ULX pulsars. These pulsars require models specifically tailored to account for their unique accretion physics, distinct from those used for Galactic black hole binaries. The X-ray spectra of all Galactic accreting X-ray pulsars (including sources in the Magellanic Clouds) are dominated by a high energy cut-off power-law and some of the sources show a soft excess, some emission lines, cyclotron absorption features, etc. In this work, we undertake a comprehensive analysis of the broadband X-ray spectra of five ULX pulsars using simultaneous XMM-Newton and NuSTAR observations and show that their X-ray spectra can be effectively described by spectral models, similar to those used for the local accretion-powered X-ray pulsars. A soft excess is detected in all the sources which is also consistent with the local X-ray pulsars that have low absorption column density. We have marginal detection or low upper limit on the presence of the iron K-alpha emission line from these sources, which is a key difference of the ULX pulsars with the local accreting X-ray pulsars. We discuss the implication of this on the nature of the binary companion and the accretion mechanism in the ULX pulsars.

Retina-Inspired X-Ray Optoelectronic Synapse Using Amorphous Ga2O3 Thin Film.

Machine vision techniques are widely applied for object identification in daily life and industrial production, where images are captured and processed by sensors, memories, and processing units sequentially. Neuromorphic optoelectronic synapses, as a preferable option to promote the efficiency of image recognition, are hotly pursued in non-ionizing radiation range, but rarely in ionizing radiation including X-rays. Here, the study proposes an X-ray optoelectronic synapse using amorphous Ga2O3 (a-Ga2O3) thin film. Boosted by the interfacial VO 2+ defects and its slow neutralization rate, the enhanced electron tunneling process at metal/a-Ga2O3 interface produces remarkable X-ray-induced post-synaptic current, contributing to a sensitivity of 20.5, 64.3, 164.1 µC mGy-1 cm-2 for the 1st, 5th, and 10th excitation periods, respectively. Further, a 64×64 imaging sensor is constructed on a commercial amorphous Si (a-Si) thin film transistor (TFT) array. The image contrast can be apparently improved under a series of X-ray pulses due to an outstanding long-term plasticity of the single pixel, which is beneficial to the subsequent image recognition and classification based on artificial neural network. The merits of large-scale production ability and good compatibility with modern microelectronic techniques belonging to amorphous oxide semiconductors may promote the development of neuro-inspired X-ray imagers and corresponding machine vision systems.

Millisecond pulsars phenomenology under the light of graph theory

We compute and apply the minimum spanning tree (MST) of the binary millisecond pulsar population, and discuss aspects of the known phenomenology of these systems in this context. We find that the MST effectively separates different classes of spider pulsars ---eclipsing radio pulsars in tight binary systems with a companion of either sim 0.1–0.8 M$_ (redbacks) or $ M$_ in mass (black widows)--- into distinct branches. The MST also separates black widows (BWs) in globular clusters from those found in the field and groups other pulsar classes of interest, including transitional millisecond pulsars (tMSPs). Using the MST and a defined ranking for similarity, we identify possible candidates likely to belong to these pulsar classes. In particular, based on this approach, we propose the BW classification of J1300+1240, J1630+3550, J1317-0157, J1221-0633, J1627+3219, J1737-0314A, and J1701-3006F, discuss that of J1908+2105, and analyze J1723-2837, J1431-4715, and J1902-5105 as possible transitional systems. We introduce an algorithm that quickly locates where new pulsars fall within the MST and use this to examine the positions of the tMSP IGR J18245-2452 (PSR J1824-2452I), the tMSP candidate 3FGL J1544.6-1125, and the accreting millisecond X-ray pulsar SAX J1808.4-3658. Assessing the positions of these sources in the MST ---assuming a range for their unknown variables (e.g., the spin period derivative of PSR J1824-2452I)---, we can effectively narrow down the parameter space necessary for searching for and determining key pulsar parameters through targeted observations.

Prediction of Fragility Fractures and Mortality in a Cohort of Geriatric Patients.

Risk factors of refracture after fragility fractures include osteoporosis, female gender and advanced age among others. We hypothesized that the assessment of functionality, muscle health and nutrition status contribute to the risk prediction for further fractures and death. We assessed 334 patients admitted to the department of acute geriatrics for sociodemographic data, bone fragility, selected laboratory tests, body composition and data on functionality using the comprehensive geriatric assessment. Patients had follow-ups until the occurrence of further fractures or death. Dual-energy X-ray absorptiometry and pulse echo measurements were performed to assess bone mineral density. Fracture risk was assessed using the FRAX score and muscle strength according to published guidelines on sarcopenia. The mean age was 81 years (70-95), and 82.3% (275/334) were women. An incidence of 10.4% (35/334) new fragility fractures was observed within 24 months, and the mortality rate was 12.2% (41/334). A significantly higher rate of further fractures was associated with lower BMI (body mass index) (HR 0.925, CI 0.872-0.98; p = 0.009), lower parathyroid hormone levels (HR 0.986, CI 0.973-0.998; p = 0.026) and with the diagnosis of osteoporosis (HR 2.546, CI 1.192-5.438; p = 0.016). No significant associations were present in patients with previous fractures, with higher age, higher FRAX scores, sarcopenia, in women, sarcopenic obesity, frail patients, lower grip strength, lower walking speed, lower Barthel index or lower DI (density index) values. The predictive power for further fractures was 10.7% higher adding osteosarcopenia, BMI and parathyroid hormone levels to standard assessment parameters osteoporosis, age and the status of previous fractures. Mortality was significantly higher with advanced age (HR 1.101, CI 1.052-1.151; p < 0.001), in men (HR 6.464, CI 3.141-13.305; p < 0.001), in smokers (p = 0.002), higher FRAX score (HR 1.039, CI 1.009-1.070; p = 0.010), lower renal function (HR 0.987, CI 0.976-0.997; p = 0.010), lower Tinetti test scores (HR 0.943, CI 0.900-0.987; p = 0.012), lower walking speed (HR 0.084, CI 0.018-0.382; p = 0.001), lower hand grip (HR 0.876, CI 0.836-0.919; p < 0.001) and lower Barthel index scores (HR 0.984, CI 0.971-0.997; p = 0.015). In a cohort of geriatric patients, the addition of BMI, low parathyroid hormone levels and osteosarcopenia increases the predictive power for further fractures by 10.7%. These parameters are a valuable addition to the standard assessment parameters age and history of sustained fractures. Mortality is partly associated with potentially treatable functional parameters.

Electron-cloud alignment dynamics induced by an intense X-ray free-electron laser pulse: a case study on atomic argon

In an intense X-ray free-electron laser (XFEL) pulse, atoms are sequentially ionised by multiple X-ray photons. Photoionisation generally induces an alignment of the electron cloud of the produced atomic ion regarding its orbital-angular-momentum projections. However, how the alignment evolves during sequential X-ray multi-photon ionisation accompanied by decay processes has been unexplored. Here we present a theoretical prediction of the time evolution of the electron-cloud alignment of argon ions induced by XFEL pulses. To this end, we calculate state-resolved ionisation dynamics of atomic argon interacting with an intense linearly polarised X-ray pulse, which generates ions in a wide range of charge states with non-zero orbital- and spin-angular momenta. Employing time-resolved alignment parameters, we predict the existence of non-trivial alignment dynamics during intense XFEL pulses. This implies that even if initially the atomic electron cloud is perfectly spherically symmetric, X-ray multi-photon ionisation can lead to noticeable reshaping of the electron cloud.

A framework to model charge sharing and pulse pileup for virtual imaging trials of photon-counting CT

Objective.This study describes the development, validation, and integration of a detector response model that accounts for the combined effects of x-ray crosstalk, charge sharing, and pulse pileup in photon-counting detectors.Approach.The x-ray photon transport was simulated using Geant4, followed by analytical charge sharing simulation in MATLAB. The analytical simulation models charge clouds with Gaussian-distributed charge densities, which are projected on a 3×3 pixel neighborhood of interaction location to compute detected counts. For pulse pileup, a prior analytical method for redistribution of energy-binned counts was implemented for delta pulses. The x-ray photon transport and charge sharing components were validated using experimental data acquired on the CdTe-based Pixirad-1/Pixie-III detector using monoenergetic beams at 26, 33, 37, and 50 keV. The pulse pileup implementation was verified with a comparable Monte Carlo simulation. The model output without pulse pileup was used to generate spatio-energetic response matrices for efficient simulation of scanner-specific photon-counting CT (PCCT) images with DukeSim, with pulse pileup modeled as a post-processing step on simulated projections. For analysis, images for the Gammex multi-energy phantom and the XCAT chest phantom were simulated at 120 kV, both with and without pulse pileup for a range of doses (27-1344 mAs). The XCAT images were evaluated qualitatively at 120 mAs, while images for the Gammex phantom were evaluated quantitatively for all doses using measurements of attenuation coefficients and Calcium concentrations.Main results.Reasonable agreement was observed between simulated and experimental spectra with Mean Absolute Percentage Error Values (MAPE) between 10%and 31%across all incident energies and detector modes. The increased pulse pileup from increased dose affected attenuation coefficients and calcium concentrations, with an effect on calcium quantification as high as MAPE of 28%.Significance.The presented approach demonstrates the viability of the model for enabling VITs to assess and optimize the clinical performance of PCCT.

“Beam à la carte”: Laser heater shaping for attosecond pulses in a multiplexed x-ray free-electron laser

Electron beam shaping allows the control of the temporal properties of x-ray free-electron laser pulses from femtosecond to attosecond timescales. Here, we demonstrate the use of a laser heater to shape electron bunches and enable the generation of attosecond x-ray pulses. We demonstrate that this method can be applied in a selective way, shaping a targeted subset of bunches while leaving the remaining bunches unchanged. This experiment enables the delivery of shaped x-ray pulses to multiple undulator beamlines, with pulse properties tailored to specialized scientific applications.

Probing the polarized emission from SMC X-1: The brightest X-ray pulsar observed by IXPE

Recent observations of X-ray pulsars (XRPs) performed by the Imaging X-ray Polarimetry Explorer (IXPE) have made it possible to investigate the intricate details of these objects in a new way, thanks to the added value of X-ray polarimetry. Here we present the results of the IXPE observations of SMC X-1, a member of the small group of XRPs displaying super-orbital variability. SMC X-1 was observed by IXPE three separate times during the high state of its super-orbital period. The observed luminosity in the 2–8 keV energy band of L ∼ 2 × 1038 erg s−1 makes SMC X-1 the brightest XRP ever observed by IXPE. We detect significant polarization in all three observations, with values of the phase-averaged polarization degree (PD) and polarization angle (PA) of 3.2 ± 0.8% and 97° ±8° for Observation 1, 3.0 ± 0.9% and 90° ±8° for Observation 2, and 5.5 ± 1.1% and 80° ±6° for Observation 3, for the spectro-polarimetric analysis. The observed PD shows an increase over time with decreasing luminosity, while the PA decreases in decrements of ∼10°. The phase-resolved spectro-polarimetric analysis reveals significant detection of polarization in three out of seven phase bins, with the PD ranging between ∼2% and ∼10%, and a corresponding range in the PA from ∼70° to ∼100°. The pulse-phase resolved PD displays an apparent anti-correlation with the flux. Using the rotating vector model, we obtain constraints on the pulsar’s geometrical properties for the individual observations. The position angle of the pulsar displays an evolution over time supporting the idea that we observe changes related to different super-orbital phases. Scattering in the wind of the precessing accretion disk may be responsible for the behavior of the polarimetric properties observed during the high-state of SMC X-1’s super-orbital period.

A novel method for rapidly simulating X-ray pulsar signals at a spacecraft

This paper addresses the challenges posed by the low photon flux and limited atmospheric penetration capabilities of X-ray pulsar signals, which are further exacerbated by technical, economic, and temporal constraints during in-orbit observations. These challenges result in a lack of continuous and high-fidelity data support for ground-based X-ray pulsar navigation (XPNAV) research and validation. To overcome these obstacles, we propose an innovative method for the efficient and rapid simulation of X-ray pulsar signals as received by spacecraft. Building on the physical process that, although the arrival times of the same pulsar signal differ between the spacecraft and the Solar System Barycenter (SSB), these times can be calibrated to the same phase at the SSB using a timing model, we leverage the relationship between the pulsar signal’s arrival rate at the SSB and its arrival phase. Using the Order Statistical Method (OSM), we directly and effectively generate the arrival phase series of pulsar signals received by the spacecraft, which follow a non-homogeneous Poisson process (NHPP). Subsequently, from these phase series, we derive the arrival time series of spacecraft-received pulsar signals, incorporating multiple physical effects based on a relationship model between arrival time series and phases. This method significantly reduces the required simulation time while maintaining high accuracy, thereby greatly enhancing simulation efficiency. Validation against data from the Rossi X-ray Timing Explorer (RXTE) and the Neutron Star Interior Composition Explorer (NICER) shows that the correlation coefficients between the accumulated profiles of simulated and measured data exceed 0.99. Furthermore, our method reduces the simulation time of high-flux pulsar signals by 25.7%, high spin frequency signals by 40.8%, and long observation duration signals by 25.38% compared to the latest fast simulation techniques, highlighting its advantages in accuracy, speed, and versatility for simulating pulsar signals across varying flux rates, spin frequencies, and observation durations. This approach provides continuous and effective data support for XPNAV research, significantly advancing theoretical and practical developments in the field.

X-ray communication system with high-repetition-rate pulsed X-ray source and LYSO(Ce) and YAP(Ce) scintillators

X-ray communication offers significant advantages over traditional microwave methods due to its shorter wavelength and higher theoretical bandwidth, enabling efficient space communication and penetration through complex electromagnetic environments. However, current systems face limitations in X-ray emission modulation and high-precision timing detection. To meet the high-frequency transmission demands of space missions, we developed a pulsed X-ray emission source capable of high-frequency modulation. Additionally, we identified specific scintillators with distinct advantages for different transmission frequency ranges, allowing for performance optimization. Experimental results demonstrated a successful transmission rate of 10 MHz, validating the feasibility of MHz-frequency X-ray communication.

Spectral and timing properties of the accreting millisecond X-ray pulsar IGR J17498−2921 during its 2023 outburst

We present a comprehensive study of the spectral properties of the accreting millisecond X-ray pulsar IGR J17498−2921 during its 2023 outburst. Similar to other accreting millisecond X-ray pulsars, the broadband spectral emission observed quasi-simultaneously by NICER and NuSTAR is well described by an absorbed Comptonized emission with an electron temperature of ∼17 keV plus a disk reflection component. The broadening of the disk reflection spectral features, such as a prominent iron emission line at 6.4–6.7 keV, is consistent with the relativistic motion of matter in a disk truncated at ∼21 Rg from the source, near the Keplerian corotation radius. From the high-cadence monitoring data obtained with NICER, we observed that the evolution of the photon index and the temperature of seed photons tracks variations in the X-ray flux. This is particularly evident close to a sudden ∼–0.25 cycle jump in the pulse phase, which occurs immediately following an X-ray flux flare and a drop in the pulse amplitude below the 3σ detection threshold. We also report on the non-detection of optical pulsations with TNG/SiFAP2 from the highly absorbed optical counterpart.

A NICER View of PSR J1231−1411: A Complex Case

Recent constraints on neutron star mass and radius have advanced our understanding of the equation of state (EOS) of cold dense matter. Some of them have been obtained by modeling the pulses of three millisecond X-ray pulsars observed by the Neutron Star Interior Composition Explorer (NICER). Here, we present a Bayesian parameter inference for a fourth pulsar, PSR J1231−1411, using the same technique with NICER and XMM-Newton data. When applying a broad mass-inclination prior from radio timing measurements and the emission region geometry model that can best explain the data, we find likely converged results only when using a limited radius prior. If limiting the radius to be consistent with the previous observational constraints and EOS analyses, we infer the radius to be 12.6 ± 0.3 km and the mass to be 1.04−0.03+0.05 M ⊙, each reported as the posterior credible interval bounded by the 16% and 84% quantiles. If using an uninformative prior but limited between 10 and 14 km, we find otherwise similar results, but Req=13.5−0.5+0.3 km for the radius. In both cases, we find a nonantipodal hot region geometry where one emitting spot is at the equator or slightly above, surrounded by a large colder region, and where a noncircular hot region lies close to southern rotational pole. If using a wider radius prior, we only find solutions that fit the data significantly worse. We discuss the challenges in finding the better fitting solutions, possibly related to the weak interpulse feature in the pulse profile.

Element-specific ultrafast lattice dynamics in FePt nanoparticles

Light–matter interaction at the nanoscale in magnetic alloys and heterostructures is a topic of intense research in view of potential applications in high-density magnetic recording. While the element-specific dynamics of electron spins is directly accessible to resonant x-ray pulses with femtosecond time structure, the possible element-specific atomic motion remains largely unexplored. We use ultrafast electron diffraction (UED) to probe the temporal evolution of lattice Bragg peaks of FePt nanoparticles embedded in a carbon matrix following excitation by an optical femtosecond laser pulse. The diffraction interference between Fe and Pt sublattices enables us to demonstrate that the Fe mean square vibration amplitudes are significantly larger that those of Pt as expected from their different atomic mass. Both are found to increase as energy is transferred from the laser-excited electrons to the lattice. Contrary to this intuitive behavior, we observe a laser-induced lattice expansion that is larger for Pt than for Fe atoms during the first picosecond after laser excitation. This effect points to the strain-wave driven lattice expansion with the longitudinal acoustic Pt motion dominating that of Fe.

A Catalog of Pulsar X-Ray Filaments

Abstract We present the first Chandra X-ray Observatory (CXO) catalog of “pulsar X-ray filaments,” or “misaligned outflows.” These are linear, synchrotron-radiating features powered by ultrarelativistic electrons and positrons that escape from bow shock pulsars. The filaments are misaligned with the (large) pulsar velocity, distinguishing them from the pulsar wind nebula (PWN) trail, which is also often visible in CXO ACIS images. Spectral fits and morphological properties are extracted for five secure filaments and three candidates using a uniform method. We present a search of archival CXO data for linear diffuse features; the known examples are recovered and a few additional weak candidates are identified. We also report on a snapshot CXO ACIS survey of pulsars with properties similar to the filament producers, finding no new filaments but some diffuse emission, including one PWN trail. Finally, we provide an updated model for the pulsar properties required to create filaments in light of these new observations.

Broadband X-ray spectral and timing properties of the accreting millisecond X-ray pulsar IGR J17498−2921 during the 2023 outburst

We report on the broadband spectral and timing properties of the accreting millisecond X-ray pulsar IGR J17498−2921 during its April 2023 outburst. We used data from NICER (1–10 keV), NuSTAR (3–79 keV), Insight-HXMT (2–150 keV), and INTEGRAL (30–150 keV). We detected significant 401 Hz pulsations across the 0.5–150 keV band. The pulse fraction increases from ∼2% at 1 keV to ∼13% at 66 keV. We detected five type-I X-ray bursts, including three photospheric radius expansion bursts, with a rise time of ∼2 s and an exponential decay time of ∼5 s. The recurrence time is ∼9.1 h, which can be explained by unstable thermonuclear burning of hydrogen-deficient material on the neutron star surface. The quasi-simultaneous 1–150 keV broadband spectra from NICER, NuSTAR and INTEGRAL can be aptly fitted by an absorbed reflection model, relxillCp, and a Gaussian line of instrumental origin. The Comptonized emission from the hot corona is characterized by a photon index Γ of ∼1.8 and an electron temperature kTe of ∼40 keV. We obtained a low inclination angle i ∼ 34°. The accretion disk shows properties of strong ionization, log(ξ/erg cm s−1)∼4.5, over-solar abundance, AFe ∼ 7.7, and high density, log(ne/cm−3)∼19.5. However, a lower disk density with normal abundance and ionization could also be possible. Based on the inner disk radius of Rin = 1.67RISCO and the long-term spin-down rate of −3.1(2)×10−15 Hz s−1, we were able to constrain the magnetic field of IGR J17498−2921 to the range of (0.9 − 2.4)×108 G.

Effects of 10 keV Electron Irradiation on the Performance Degradation of SiC Schottky Diode Radiation Detectors

The silicon carbide (SiC) Schottky diode (SBD) detector in a SiC hybrid photomultiplier tube (HPMT) generates signals by receiving photocathode electrons with an energy of 10 keV. So, the performance of the SiC SBD under electron irradiation with an energy of 10 keV has an important significance for the application of the SiC-HPMT. However, studies on 10 keV radiation effects on the SiC SBDs were rarely reported. In this paper, the performance degradation of the SiC SBDs irradiated by 10 keV electrons at different fluences was investigated. After the irradiation, the forward current of the SiC SBDs increased, and the turn-on voltage decreased with the irradiation fluences until 1.6 × 1016 cm−2. According to the capacitance–voltage (C-V) curves, the effective doping concentration increased slightly after the irradiation, and an obvious discrepancy of C-V curves occurred below 5 V. Moreover, as a radiation detector, the peak position of the α-particles’ amplitude spectrum changed slightly, and the energy resolution was also slightly reduced after the irradiation due to the high collection charge efficiency (CCE) still being larger than 99.5%. In addition, the time response of the SiC SBD to the 50 ns pulsed X-ray was almost not affected by the irradiation. The results indicated that the performance degradation of the SiC SBD irradiated at the fluence of 1.5 × 1017 cm−2 would not result in a deterioration of the properties of the SiC-HPMT and showed an important significance for the supplement of the radiation resistance of the SiC SBD radiation detector.

Inferring system parameters from the bursts of the accretion-powered pulsar IGR J17498–2921

ABSTRACT Thermonuclear (type-I) bursts exhibit properties that depend both on the local surface conditions of the neutron stars on which they ignite, as well as the physical parameters of the host binary system. However, constraining the system parameters requires a comprehensive method to compare the observed bursts to simulations. We have further developed the beansp code for this purpose and analysed the bursts observed from IGR J17498$-$2921, a 401-Hz accretion-powered pulsar, discovered during it’s 2011 outburst. We find good agreement with a model having H-deficient fuel with $X=0.15\pm 0.4$, and CNO metallicity $Z=0.0014^{+0.0004}_{-0.0003}$, about a tenth of the solar value. The model has the system at a distance of $5.7^{+0.6}_{-0.5}$ kpc, with a massive (${\approx} 2\ \mathrm{ M}_\odot$) neutron star and a likely inclination of $60^\circ$. We also re-analysed the data from the 2002 outburst of the accretion-powered millisecond pulsar SAX J1808.4$-$3658. For that system we find a substantially closer distance than previously inferred, at $2.7\pm 0.3$ kpc, likely driven by a larger degree of burst emission anisotropy. The other system parameters are largely consistent with the previous analysis. We briefly discuss the implications for the evolution of these two systems.

XFEL SASE pulses can enhance time-dependent observables

Abstract X-ray free electron lasers (XFELs) have emerged as powerful sources of short and intense X-ray pulses. We propose a simple and robust procedure which takes advantage of the inherent stochasticity of self-amplified stimulated emission (SASE) pulses to enhance the time-resolution and signal strength in the recorded data. Notably, the proposed method is able to enhance the average signal without knowledge of the signal strength of individual shots. Simple metrics for the probe pulses are introduced, such as an effective pulse duration applicable to SASE pulses characterised in the time domain using {\it{e.g.}}\ an X-band transverse cavity (XTCAV). The approach is evaluated using simulated and real pulse data in the context of ultrafast electron dynamics in a molecule. Utilising H$_2$ as a model system, we demonstrate the efficacy of the method theoretically, successfully enhancing the predicted nonresonant ultrafast X-ray scattering signal associated with electron dynamics. The method presented is broadly applicable and offers a general strategy for enhancing time-dependent observables at XFELs.

Observation of molecular resonant double-core excitation driven by intense X-ray pulses

The ultrashort and intense pulses of X-rays produced at X-ray free electron lasers (XFELs) have enabled unique experiments on the atomic level structure and dynamics of matter, with time-resolved studies permitted in the femto- and attosecond regimes. To fully exploit them, it is paramount to obtain a comprehensive understanding of the complex nonlinear interactions that can occur at such extreme X-ray intensities. Herein, we report on the experimental observation of a resonant double-core excitation scheme in N2, where two 1σ core-level electrons are resonantly promoted to unoccupied 1πg*\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$1{\\pi }_{g}^{* }$$\\end{document} molecular orbitals by a single few-femtosecond broad-bandwidth XFEL pulse. The production of these neutral two-site double core hole states is evidenced through their characteristic decay channels, which are observed in good agreement with high-level theoretical calculations. Such multi-core excitation schemes, benefiting from the high interaction cross sections and state- and site-selective nature of resonant X-ray interactions, should be generally accessible in XFEL irradiated molecules, and provide interesting opportunities for chemical analysis and for monitoring ultrafast dynamic processes.

The high-energy cyclotron line in 2S 1417-624 discovered with Insight-HXMT during the 2018 outburst

We report a detailed timing and spectral analysis of the X-ray pulsar 2S 1417-624 using the data from Insight-HXMT during the 2018 outburst. The pulse profiles are highly variable with respect to both unabsorbed flux and energy. A double-peaked pulse profile from the low flux evolved to a multi-peaked shape in the high-flux state. The pulse fraction is negatively correlated to the source flux in the range of sim (1--6)$\ $ erg cm$^ $ s$^ $, consistent with Rossi X-ray Timing Explorer (RXTE) studies during the 2009 giant outburst. The energy-resolved pulse profiles around the peak outburst showed a four-peak shape in the low-energy bands and gradually evolved to triple peaks at higher energies. The continuum spectrum is well described by typical phenomenological models, such as the cut-off power law and the power law with high-energy cut-off models. Notably, we discovered high-energy cyclotron resonant scattering features (CRSFs) for the first time, which are around 100 keV with a statistical significance of sim 7sigma near the peak luminosity of the outburst. This CRSF line is significantly detected with different continuum models and provides very robust evidence for its presence. Furthermore, pulse-phase-resolved spectroscopy confirmed the presence of the line, whose energy varied from 97 to 107 keV over the pulse phase and appeared to have a maximum value at the narrow peak phase of the profiles.