keV X-ray Research Articles

Survey of Bare Active Galactic Nuclei in the Local Universe (z < 0.2). I. On the Origin of Soft Excess

We analyze a sample of 21 “bare” Seyfert 1 active galactic nuclei, a subclass of Seyfert 1 galaxies, with intrinsic absorption N H ∼ 1020 cm−2, in the local Universe (z < 0.2) using XMM-Newton and Swift/XRT observations. The luminosities of the primary continuum, the X-ray emission in the 3–10 keV energy range, and the soft excess—the excess emission that appears above the low-energy extrapolation of the power-law fit of 3–10 keV X-ray spectra—are calculated. Our spectral analysis reveals that the long-term intrinsic luminosities of the soft excess and the primary continuum are tightly correlated . We also found that the luminosities are correlated for each source. This result suggests that both the primary continuum and soft excess emissions exhibit a dependency on the accretion rate in a similar way.

Radiosensitizing Effect of Dextran-Coated Iron Oxide Nanoparticles on Malignant Glioma Cells.

The potential of standard methods of radiation therapy is limited by the dose that can be safely delivered to the tumor, which could be too low for radical treatment. The dose efficiency can be increased by using radiosensitizers. In this study, we evaluated the sensitizing potential of biocompatible iron oxide nanoparticles coated with a dextran shell in A172 and Gl-Tr glioblastoma cells in vitro. The cells preincubated with nanoparticles for 24 h were exposed to ionizing radiation (X-ray, gamma, or proton) at doses of 0.5-6 Gy, and their viability was assessed by the Resazurin assay and by staining of the surviving cells with crystal violet. A statistically significant effect of radiosensitization by nanoparticles was observed in both cell lines when cells were exposed to 35 keV X-rays. A weak radiosensitizing effect was found only in the Gl-Tr line for the 1.2 MeV gamma irradiation and there was no radiosensitizing effect in both lines for the 200 MeV proton irradiation at the Bragg peak. A slight (ca. 10%) increase in the formation of additional reactive oxygen species after X-ray irradiation was found when nanoparticles were present. These results suggest that the nanoparticles absorbed by glioma cells can produce a significant radiosensitizing effect, probably due to the action of secondary electrons generated by the magnetite core, whereas the dextran shell of the nanoparticles used in these experiments appears to be rather stable under radiation exposure.

X-ray polarization properties of partially ionized equatorial obscurers around accreting compact objects

ABSTRACT We present the expected X-ray polarization signal resulting from distant reprocessing material around black holes. Using a central isotropic power-law emission at the centre of the simulated model, we add distant equatorial and axially symmetric media that are covering the central accreting sources. We include partial ionization and partial transparency effects, and the impact of various polarization and steepness of the primary radiation spectrum. The results are obtained with the Monte Carlo code STOKES that considers both line and continuum processes and computes the effects of scattering and absorption inside static homogenous wedge-shaped and elliptical toroidal structures, varying in relative size, composition and distance to the source. We provide first order estimates for parsec-scale reprocessing in Compton-thin and Compton-thick active galactic nuclei, as well as winds around accreting stellar-mass compact objects, for observer’s inclinations above and below the grazing angle. The resulting reprocessed polarization can reach tens of per cent with either parallel or perpendicular orientation with respect to the axis of symmetry, depending on subtle details of the geometry, density, and ionization structure. We also show how principal parameters constrained from X-ray spectroscopy or polarimetry in other wavelengths can lift the shown degeneracies in X-ray polarization. We provide an application example of the broad modelling discussion by revisiting the recent IXPE 2–8 keV X-ray polarimetric observation of the accreting stellar-mass black hole in Cygnus X-3 from the perspective of partial transparency and ionization of the obscuring outflows.

Signatures of feedback in the spectacular extended emission region of NGC 5972

ABSTRACT We present Chandra X-ray Observatory observations and Space Telescope Imaging Spectrograph spectra of NGC 5972, one of the 19 ‘Voorwerpjes’ galaxies. This galaxy contains an extended emission-line region (EELR) and an arcsecond scale nuclear bubble. NGC 5972 is a faded active galactic nucleus (AGN), with EELR luminosity suggesting a 2.1 dex decrease in Lbol in the last ∼5 × 104 yr. We investigate the role of AGN feedback in exciting the EELR and bubble given the long-term variability and potential accretion state changes. We detect broad-band (0.3–8 keV) X-ray emission in the near-nuclear regions, coincident with the [O iii] bubble, as well as diffuse soft X-ray emission coincident with the EELR. The soft nuclear (0.5–1.5 keV) emission is spatially extended and the spectra are consistent with two apec thermal populations (∼0.80 and ∼0.10 keV). We find a bubble age &amp;gt;2.2 Myr, suggesting formation before the current variability. We find evidence for efficient feedback with $P_{\textrm {kin}}/L_{\textrm {bol}}\sim 0.8~{{\ \rm per\ cent}}$, which may be overestimated given the recent Lbol variation. [O iii] kinematics show a 300 km s−1 high-ionization velocity consistent with disturbed rotation or potentially the line-of-sight component of a ∼780 km s−1 thermal X-ray outflow capable of driving strong shocks to photoionize the precursor material. We explore possibilities to explain the overall jet, radio lobe and EELR misalignment including evidence for a double supermassive black hole which could support a complex misaligned system.

Impact of total ionizing dose on the alpha-soft error rate in FDSOI 28 nm SRAMs

Synergy effect of total ionizing dose (TID) on alpha-soft error rate (α-SER) in FDSOI 28 nm SRAM has been experimentally characterized using a dedicated setup combining alpha-particle irradiation (241Am solid source) in vacuum chamber and 10 keV X-ray irradiation. Measurements have been performed on a 3 Mbit single-port SRAM cut powered at 1 V. Irradiations up to 125 krad(Si) have been achieved and their impact on the α-SER has been characterized from the cumulated number of bitflips as a function of the exposition time to the alpha-source. Modelling and simulation have been used to link transistor threshold voltage variations to SRAM cell stability in terms of static noise margin (SNM), critical charge (Qcrit) and finally estimated SER, in good agreement with experimental results.

High linear energy transfer (LET) nature of alanine radical yield by soft X-ray irradiations studied by electron spin resonance (ESR) applications

Radicals produced in alanine by irradiation of 2–7 keV X-rays were investigated by ESR applications; i.e., CW-ESR, pulse-ESR and ESR imaging. The relative radical yield decreased with the decreasing photon energy and the increasing dose. The 2D imaging showed that the radical concentration at the surface was extremely low even though the absorption of X-rays exponentially decreased with the penetration depth. The depth of the radical concentration peak was almost the same as the penetration depth for the X-ray irradiation with an energy lower than 5-keV. The product formed by radical recombination was observed by an LC/MS (liquid chromatograph-mass spectrum) analysis. For the soft X-ray irradiation, many radicals will be lost by the efficient radical-radical recombination due to the higher density of the radicals, similar to the high-LET irradiation by heavy ions. The spin-spin relaxation rate (1/T2), which correlates with the radical concentration, increased by the decreasing photon energy. The values of 1/T2 for the soft X-rays were compatible to that for the heavy ions with the high-LET. Based on these observations, it is concluded that the effects of irradiation by soft X-rays are similar to high-LET irradiation.

Multiple scattering double Compton model: determination of intrinsic efficiencies by calculating electron energies

ABSTRACT For the measurement of the energy spectra generated by photons up to 320 keV (X-rays) that can be considered by the superposition of a set of monoenergetic photons, several types of detectors have been used, mainly Ge detectors. Each spectrum can be considered as the superposition of a beam of monoenergetic photons that contain a photoelectric peak, a Compton distribution, the characteristic radiation, and a multiple scattering region, which is located between the Compton edge and the photoelectric peak. In this article, a theoretical model is developed for finding the multiple scattering region. To this end, double Compton scattering is proposed, wherein the electron in motion after the first collision suffers a second Compton scattering by a photon going in the same direction. Using the theory of special relativity and the Lorentz invariants, the kinetic energy of the electron in motion is calculated. Then, with the obtained value and the new Klein–Nishina formula, the cross-section of the absorbed electrons is calculated as a function of its kinetic energy. The model fits correctly for the multiple scattering region from four sources with a conventional multichannel analyser and its associated electronics.

A Chandra X-ray study of millisecond pulsars in the globular cluster Omega Centauri: a correlation between spider pulsar companion mass and X-ray luminosity

ABSTRACT Millisecond pulsars (MSPs) are faint X-ray sources commonly observed in Galactic globular clusters (GCs). In this work, we investigate 18 MSPs newly found in the GC Omega Centauri (ω Cen) and search for their X-ray counterparts using Chandra observations with a total exposure time of 290.9 ks. We identify confident X-ray counterparts for 11 of the MSPs, with 9 of them newly identified in this work based on their positions, spectral properties, and X-ray colours. The X-ray spectra of nine MSPs are well described by a neutron star hydrogen atmosphere model, while two MSPs are well fitted by a power-law model. The identified MSPs have X-ray luminosities ranging from 1.0 × 1030 to 1.4 × 1031 erg s−1. Additionally, for population comparison purposes, we study the X-ray counterpart to MSP E in the GC M71, and find its X-ray spectrum is well described by blackbody-like models with a luminosity of 1.9 × 1030 erg s−1. We investigate the empirical correlations between X-ray luminosities and minimum companion masses, as well as mass functions, of spider pulsars. Clear correlations are observed, with best-fitting functions of log10LX = (1.0 ± 0.1)log10Mc, min + (32.5 ± 0.2) and (0.35 ± 0.04)log10MF + (32.71 ± 0.20), respectively, with an intrinsic scatter of log10LX of ∼0.3, where LX is the 0.5–10 keV X-ray luminosity, Mc, min is the minimum companion mass, and MF represents the mass function, in solar masses.

Exploring the High-Pressure Phases of Carbon through X-ray Diffraction of Dynamic Compression Experiments on Sandia’s Z Pulsed Power Facility

The carbon phase diagram is rich with polymorphs which possess very different physical and optical properties ideal for different scientific and engineering applications. An understanding of the dynamically driven phase transitions in carbon is particularly important for applications in inertial confinement fusion, as well as planetary and meteorite impact histories. Experiments on the Z Pulsed Power Facility at Sandia National Laboratories generate dynamically compressed high-pressure states of matter with exceptional uniformity, duration, and size that are ideal for investigations of fundamental material properties. X-ray diffraction (XRD) is an important material physics measurement because it enables direct observation of the strain and compression of the crystal lattice, and it enables the detection and identification of phase transitions. Several unique challenges of dynamic compression experiments on Z prevent using XRD systems typically utilized at other dynamic compression facilities, so novel XRD diagnostics have been designed and implemented. We performed experiments on Z to shock compress carbon (pyrolytic graphite) samples to pressures of 150–320 GPa. The Z-Beamlet Laser generated Mn-Heα (6.2 keV) X-rays to probe the shock-compressed carbon sample, and the new XRD diagnostics measured changes in the diffraction pattern as the carbon transformed into its high-pressure phases. Quantitative analysis of the dynamic XRD patterns in combination with continuum velocimetry information constrained the stability fields and melting of high-pressure carbon polymorphs.

High-resolution 3D grain orientation mapping by inclined scanning 3D X-ray diffraction microscopy

The microstructure of a material plays a crucial role in determining its mechanical and chemical properties, as well as in predicting potential malfunctions. In polycrystalline materials, the orientation of each grain has a significant impact on the material's properties. It is thus imperative to conduct non-destructive 3D observations of the grain orientation with high resolution. This study presents a novel method to enhance the spatial resolution of 3D grain orientation maps in scanning 3D X-ray diffraction (S3DXRD) microscopy beyond the size of the probe beam. The new method, inclined scanning 3D X-ray diffraction (iS3DXRD) microscopy, combines an inclined geometry for the rotation axis of the object with the concept of `sub-voxel' analysis, where the voxel is subdivided into smaller pieces. The validity of the method was verified for a polycrystalline α-Fe wire using a 37 keV X-ray beam with a size of 10 × 20 µm (horizontal × vertical), and it successfully produced a high-resolution 3D grain orientation map with a spatial resolution of about 2.5 µm. The method can provide complex details on the microstructure of a polycrystalline material, which will pave the way for precise prediction of the material's properties.

Observational properties of accreting neutron stars with an optically thick envelope

ABSTRACT Pulsating ultraluminous X-ray sources are thought to be X-ray bright, accreting, magnetized neutron stars. Their measured soft (&amp;lt;20 keV) X-ray luminosity can exceed the Eddington luminosity for a neutron star by a few orders of magnitude. Although several scenarios have been proposed to explain the different components observed in the X-ray spectrum and the characteristics of the X-ray pulse profile of these systems, detailed quantitative calculations are still missing. In particular, the observed soft X-ray pulse profiles are almost sinusoidal and show an increase in the pulsed fraction (from 8 up to even 30 per cent) with increasing energy. In this work, we discuss how emission originating from an optically thick envelope, expected to be formed during super-Eddington accretion, can match the observed spectra and pulse profiles.

Response characteristics of MAPbBr3 direct conversion X-ray detectors based on measurements and Monte Carlo simulation

In recent years, higher requirements have been placed on the response characteristics of X-ray detectors in the field of medical diagnostic imaging. Due to this, high sensitivity, high attenuation coefficient and low cost detection materials need to be developed. In this paper, the geometric model of a detector was established by Geant4 code. The absorption efficiency and mass attenuation coefficient of MAPbBr3 crystals were calculated in the energy range of 30 keV to 100 keV. Compared with the mass attenuation coefficient of the NIST database, the deviation was within 1.39%. The signal charge number and detection sensitivity of the X-ray interaction with the MAPbBr3 crystal ware calculated. Compared with the CdTe crystal and α-Se, the MAPbBr3 crystal still had a larger detection sensitivity under a smaller applied electric field, which was approximately 9 times higher than that of α-Se. This result indicated that the detection sensitivity could be greatly improved by using a high atomic number and high charge mobility-lifetime product. Based on the simulation results, the 2 mm thick MAPbBr3 crystal exhibited the highest detection sensitivity at 60 keV X-rays, which was in agreement with the experimental results.

The state of art of μ-RWELL technology

The μ-RWELL is a single-amplification stage resistive Micro-Pattern Gaseous Detector (MPGD). The detector amplification element is realized with a single copper-clad polyimide foil micro-patterned with a blind hole (well) matrix and embedded in the readout PCB through a thin Diamond-Like-Carbon (DLC) sputtered resistive film. The introduction of the resistive layer, suppressing the transition from streamer to spark, allows to achieve large gains (≥ 104) with a single amplification stage, while partially reducing the capability to stand high particle fluxes. The simplest resistive layout, designed for low-rate applications, is based on a single-resistive layer with edge grounding. At high particle fluxes this layout suffers of a non-uniform response. In order to get rid of such a limitation different current evacuation geometries have been designed. In this work we report the study of the performance of several high rate resistive layouts tested at the CERN H8-SpS and PSI πM1 beam test facilities and with a high intensity 5.9 keV X-ray tube. These layouts fulfill the requirements for the detectors upgrades at the HL-LHC and for the experiments at the next generation colliders FCC-ee/hh and CepC.The possibility to realise the detector on flexible elements opens the way to use the technology for non-planar geometry such as the instrumentation of the Inner Tracker at future Charm-Tau factories. In addition, it must be stressed that the μ-RWELL device can be manufactured with full sequential-build-up technology, thus allowing a straightforward technology transfer of the manufacturing process to the industry.

Anticipating the XRISM search for the decay of resonantly produced sterile neutrino dark matter

ABSTRACT The sterile neutrino (N1) features in multiple extensions of the standard model and is a compelling dark matter candidate, especially as the decay of N1 with mass ms = 7.1 keV is a possible source for the unexplained 3.55 keV X-ray line reported in galaxy clusters. This particle will be accessible to the XRISM X-ray mission over the next 12 months. We revisit the physics behind N1 and the uncertainty in its parameters. We compare predictions for the ms = 7.1 keV N1 mixing angle, $\sin ^{2}(2\theta)\,$, and half-mode mass, Mhm, as described in the neutrino minimal standard model (νMSM) extension to existing X-ray observations and structure formation constraints. The strongest available constraints rule out N1 as a dark matter candidate, and a more optimistic reading of the data prefers $\sin ^{2}(2\theta)\,$ = 5 × 10−11 and Mhm = 3.5 × 108 ${\, \rm M_\odot }$. We highlight that the most promising upcoming opportunity for a detection is to find a line of velocity dispersion ∼500 $\, {\rm km}\, {\rm s}^{-1}$ in the Virgo cluster with XRISM, and then draw up a list of future objects of study to determine: (i) whether the line is from dark matter generally, and (ii) if from dark matter, whether that candidate is indeed N1.

Delayed appearance and evolution of coronal lines in the TDE AT2019qiz

ABSTRACT Tidal disruption events (TDEs) occur when a star gets torn apart by a supermassive black hole as it crosses its tidal radius. We present late-time optical and X-ray observations of the nuclear transient AT2019qiz, which showed the typical signs of an optical-UV transient class commonly believed to be TDEs. Optical spectra were obtained 428, 481, and 828 rest-frame days after optical light-curve peak, and a UV/X-ray observation coincided with the later spectrum. The optical spectra show strong coronal emission lines, including [Fe vii], [Fe x], [Fe xi], and [Fe xiv]. The Fe lines rise and then fall, except [Fe xiv] that appears late and rises. We observe increasing flux of narrow H α and H β and a decrease in broad H α flux. The coronal lines have full width at half-maximum ranging from ∼150−300 km s−1, suggesting they originate from a region between the broad- and narrow-line emitting gas. Between the optical flare and late-time observation, the X-ray spectrum softens dramatically. The 0.3–1 keV X-ray flux increases by a factor of ∼50, while the hard X-ray flux decreases by a factor of ∼6. Wide-field Infrared Survey Explorer fluxes also rose over the same period, indicating the presence of an infrared echo. With AT2017gge, AT2019qiz is one of two examples of a spectroscopically confirmed optical-UV TDE showing delayed coronal line emission, supporting speculations that Extreme Coronal Line Emitters in quiescent galaxies can be echos of unobserved past TDEs. We argue that the coronal lines, narrow lines, and infrared emission arise from the illumination of pre-existing material likely related to either a previous TDE or active galactic nucleus activity.

Correlated short time-scale hard-soft X-ray variability of the blazars Mrk 421 and 1ES 1959+650 using AstroSat

ABSTRACT We study simultaneous soft (0.7–7 keV) and hard (7–20 keV) X-ray light curves at a total of eight epochs during 2016–2019 of two TeV blazars Mrk 421 and 1ES 1959+650 observed by the SXT and LAXPC instruments on-board AstroSat. The light curves are 45–450 ks long and may be sampled with time bins as short as 600–800 s with high signal-to-noise ratio. The blazars show a harder when brighter trend at all epochs. Discrete cross-correlation functions indicate that the hard and soft X-ray variability are strongly correlated. The time lag is consistent with zero in some epochs, and indicates hard or soft lag of a few hours in the rest. In the leptonic model of blazar emission, soft lag may be due to slower radiative cooling of lower energy electrons while hard lag may be caused by gradual acceleration of the high energy electrons emitting at the hard X-ray band. Assuming the above scenario and the value of the Doppler factor (δ) to be 10–20, the hard and soft lags may be used to estimate the magnetic field to be ∼0.1 Gauss and the acceleration parameter to be ∼104 in the emission region. Due to the availability of the high time resolution (∼ minutes to hours) light curves from AstroSat, the value of the illusive acceleration parameter could be estimated, which provides a stringent constraint on the theories of particle acceleration in blazar jets.

ISAI: Investigating Solar Axion by Iron-57

The existence of the axion is a unique solution for the strong CP problem, and the axion is one of the most promising candidates of the dark matter. Investigating Solar Axion by Iron-57 (ISAI) is being prepared as a complemented table-top experiment to confirm the solar axion scenario. Probing an X-ray emission from the nuclear transitions associated with the axion-nucleon coupling is a leading approach. ISAI searches for the monochromatic 14.4 keV X-ray from the first excited state of ^{57}57Fe using a state-of-the-art pixelized silicon detector, dubbed XRPIX, under an extremely low-background environment. We highlight scientific objectives, experimental design and the latest status of ISAI.

3D track reconstruction of low-energy electrons in the MIGDAL low pressure optical time projection chamber

We demonstrate three-dimensional track reconstruction of electrons in a low pressure (50 Torr) optical TPC consisting of two glass GEMs with an ITO strip readout in CF4 and CF4/Ar mixtures. The reconstructed tracks show a variety of event topologies, including short tracks from photoelectrons induced by 55Fe 5.9 keV X-rays and long tracks from gamma ray interactions and beta decays. Algorithms for event identification and track ridge detection are discussed as well as multiple methods for integrating information from the camera image and ITO waveforms with the goal of full 3D reconstruction of the track.

The Large Deficit of HMXB Emission from Luminous Infrared Galaxies: The Case of the Circumnuclear Starburst Ring in NGC 7552

Luminous infrared galaxies (LIRGs), the most extreme star-forming galaxies in the nearby (D < 30 Mpc) universe, show a notable X-ray emission deficiency (up to a factor of ∼10) compared with predictions from scaling relations of galaxy-wide high-mass X-ray binary (HMXB) luminosity with star formation rate. In the nearby (≈20 Mpc) LIRG NGC 7552, the majority of the IR emission originates in a circumnuclear starburst ring, which has been resolved into several discrete knots of star formation. We present results from recent Chandra observations of NGC 7552, which reveal significant deficits in the 2–7 keV X-ray luminosities from two of the most powerful star-forming knots. We hypothesize that the expected luminous HMXB populations in these knots are either (1) obscured by very large column densities or (2) suppressed due to the knots having relatively high metallicity and/or very young ages (≲5 Myr). We distinguish between these possibilities using data from recent NuSTAR observations, whose sensitivity above 10 keV is capable of uncovering heavily obscured HMXB populations, since emission at these energies is more immune to absorption effects. We find no evidence of a heavily obscured HMXB population in the central region of NGC 7552, suggesting suppressed HMXB formation. We further show that metallicity-dependent scaling relations cannot fully account for the observed deficit from the most powerful star-forming knots or the central region as a whole. Thus, we suggest that recent bursts in local star formation activity likely drive the high L IR within these regions on timescales ≲5 Myr, shorter than the timescale required for the formation of HMXBs.

XCC: an X-ray FEL-based γγ Compton collider Higgs factory

This report describes the conceptual design of a γγ Higgs factory in which 62.8 GeV electron beams collide with 1 keV X-ray free electron laser (XFEL) beams to produce colliding beams of 62.5 GeV photons. The Higgs boson production rate is 80,000 Higgs bosons per 107 second year, roughly the same as the ILC Higgs rate at √s = 250 GeV. The electron accelerator is based on cold copper distributed coupling (C3) accelerator technology. Unlike the center-of-mass energy spectra of previous optical wavelength γγ collider designs, the sharply peaked γγ center-of-mass energy spectrum of XCC produces model independent Higgs coupling measurements with precision on par with e + e - colliders. For the triple Higgs coupling measurement, the XCC center-of-mass energy can be upgraded to 380 GeV, where the cross section for γγ → HH is twice that of e + e - → ZHH at √s = 500 GeV. Design challenges are discussed, along with the R&D to address them, including demonstrators.