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Purpose. Fast kV-switching (FKS) and dual-layer flat-panel detector (DL-FPD) technologies have been actively studied as promising dual-energy spectral imaging solutions for FPD-based cone-beam computed tomography (CT). However, cone-beam CT (CBCT) spectral imaging is known to face challenges in obtaining accurate and robust material discrimination performance. That is because the energy separation by either FKS or DL-FPD, alone, is still limited, along with apparently unpaired signal levels in the effective low- and high-energy projections in real applications, not to mention the x-ray scatter in cone-beam scan which will make the material decomposition almost impossible if no correction is applied. To further improve CBCT spectral imaging capability, this work aims to promote a source-detector joint multi-energy spectral imaging solution which takes advantages of both FKS and DL-FPD, and to conduct a feasibility study on the first tabletop CBCT system with the joint spectral imaging capability developed. Methods. For CBCT, development of multi-energy spectral imaging can be jointly realized by using an x-ray source with a generator whose kilo-voltages can alternate in tens of Hertz (i.e. FKS), and a DL-FPD whose top- and bottom-layer projections corresponds to different effective energy levels. Thanks to the complimentary characteristics inherent in FKS and DL-FPD, the overall energy separation will be significantly better when compared with FKS or DL-FPD alone, and the x-ray photon detection efficiency will be also improved when compared with FKS alone. In this work, a noise performance analysis using the Cramér–Rao lower bound (CRLB) method is conducted. The CRLB for basis material after a projection-domain material decomposition is derived, followed by a set of numerical calculations of CRLBs, for the FKS, the DL-FPD and the joint solution, respectively. To compensate for the slightly angular mismatch between low- and high- projections in FKS, a dual-domain projection completion scheme is implemented. Afterwards material decomposition from the complete projection data is carried out by using the maximum-likelihood method, followed by reconstruction of basis material and virtual monochromatic images (VMI). In this work, the first FKS and DL-FPD jointly enabled multi-energy tabletop CBCT system, to the best of our knowledge, has been developed in our laboratory. To evaluate its spectral imaging performance, a set of physics experiments are conducted, where the multi-energy and head phantoms are scanned using the 80/105/130 kVp switching pairs and projection data are collected using a prototype DL-FPD, whose both top and bottom layer of panels are composed of 550 μ m of cesium iodine (CsI) scintillators with no intermediate metal filter in-between. Results. The numerical simulations show that the joint spectral imaging solution can lead to a significant improvement in energy separation and lower noise levels in most of material decomposition cases. The physics experiments confirmed the feasibility and superiority of the joint spectral imaging, whose CNRs in the selected regions of interest of the multi-energy phantom were boosted by an average improvement of 21.9%, 20.4% for water basis images and 32.8%, 62.8% for iodine images when compared with that of the FKS and DL-FPD, respectively. For the head phantom case, the joint spectral imaging can effectively reduce the streaking artifacts as well, and the standard deviation in the selected regions of interest are reduced by an average decrement of 19.5% and 8.1% for VMI when compared with that of the FKS and DL-FPD, respectively. Conclusions. A feasibility study of the joint spectral imaging solution for CBCT by utilizing both the FKS and DL-FPD was conducted, with the first tabletop CBCT system having such a capability being developed, which exhibits improved CNR and is more effective in avoiding streaking artifacts as expected. [ABSTRACT FROM AUTHOR]

The detection of inelastically scattered soft x-rays with high energy resolution usually requires large grating spectrometers. Recently, photoelectron spectrometry for analysis of x-rays (PAX) has been rediscovered for modern spectroscopy experiments at synchrotron light sources. By converting scattered photons to electrons and using an electron energy analyser, the energy resolution for resonant inelastic x-ray scattering (RIXS) becomes decoupled from the x-ray spot size and instrument length. In this work, we develop PAX towards high energy resolution using a modern photoemission spectroscopy setup studying Ba2Cu3O4Cl2 at the Cu L 3-edge. We measure a momentum transfer range of 24% of the first Brillouin zone simultaneously. Our results hint at the observation of a magnon excitation below 100 meV energy transfer and show intensity variations related to the dispersion of dd -excitations. With dedicated setups, PAX can complement the best and largest RIXS instruments, while at the same time opening new opportunities to acquire RIXS at a range of momentum transfers simultaneously and combine it with angle-resolved photoemission spectroscopy in a single instrument. [ABSTRACT FROM AUTHOR]

Recent developments in x-ray image based pulmonary nodule detection have achieved remarkable results. However, existing methods are focused on transferring off-the-shelf coarse-grained classification models and fine-grained detection models rather than developing a dedicated framework optimized for nodule detection. In this paper, we propose PN-DetX, which as we know is the first dedicated pulmonary nodule detection framework. PN-DetX incorporates feature fusion and self-attention into x-ray based pulmonary nodule detection tasks, achieving improved detection performance. Specifically, PN-DetX adopts CSPDarknet backbone to extract features, and utilizes feature augmentation module to fuse features from different levels followed by context aggregation module to aggregate semantic information. To evaluate the efficacy of our method, we collect a LA rge-scale P ulmonary NO dule D etection dataset, LAPNOD, comprising 2954 x-ray images along with expert-annotated ground truths. As we know, this is the first large-scale chest x-ray pulmonary nodule detection dataset. Experiments demonstrates that our method outperforms baseline by 3.8% mAP and 5.1% AP 0.5. The generality of our approach is also evaluated on the publicly available dataset NODE21. We aspire for our method to serve as an inspiration for future research in the field of pulmonary nodule detection. The dataset and codes will be made in public. [ABSTRACT FROM AUTHOR]

Aim. Flat panel detectors with small pixel sizes general can potentially improve imaging performance in radiography applications requiring fine detail resolution. This study evaluated the imaging performance of seven detectors, covering a wide range of pixel sizes, in the frame of orthopaedic applications. Material and methods. Pixel sizes ranged from 175 (detector A175) to 76 μ m (detector G76). Modulation transfer function (MTF) and detective quantum efficiency (DQE) were measured using International Electrotechnical Commission (IEC) RQA3 beam quality. Threshold contrast (C T) and a detectability index (d ′) were measured at three air kerma/image levels. Rabbit shoulder images acquired at 60 kV, over five air kerma levels, were evaluated in a visual grading study for anatomical sharpness, image noise and overall diagnostic image quality by four radiologists. The detectors were compared to detector E124. Results. The 10% point of the MTF ranged from 3.21 to 4.80 mm−1, in going from detector A175 to detector G76. DQE(0.5 mm−1) measured at 2.38 μ Gy/image was 0.50 ± 0.05 for six detectors, but was higher for F100 at 0.62. High frequency DQE was superior for the smaller pixel detectors, however C T for 0.25 mm discs correlated best with DQE(0.5 mm−1). Correlation between C T and the detectability model was good (R 2 = 0.964). C T for 0.25 mm diameter discs was significantly higher for D150 and F100 compared to E124. The visual grading data revealed higher image quality ratings for detectors D125 and F100 compared to E124. An increase in air kerma was associated with improved perceived sharpness and overall quality score, independent of detector. Detectors B150, D125, F100 and G76, performed well in specific tests, however only F100 consistently outperformed the reference detector. Conclusion. Pixel size alone was not a reliable predictor of small detail detectability or even perceived sharpness in a visual grading analysis study. [ABSTRACT FROM AUTHOR]

Using the observations of the high-energy detector of the Hard X-ray Modulation Telescope (Insight-HXMT) for Scorpius X-1 from 2017 to 2020, we search for hard X-ray tails in the X-ray spectra in ∼30–200 keV. The hard X-ray tails are found throughout the Z -track on the hardness–intensity diagram, and the detected hard X-ray tails become hard and weak from the horizontal branch (HB), through the normal branch (NB), to the flaring branch (FB). Comparing the hard X-ray spectra of Insight-HXMT between Cyg X-1 and Sco X-1, it is concluded that the hard X-ray spectrum of Cyg X-1 shows a high-energy cutoff, implying a hot corona in it, but the high-energy cutoff is not seen in the hard X-ray spectrum of Sco X-1. From fitting the broadband spectrum of Sco X-1 in ∼2–200 keV, it is proposed that the hard X-ray tails in the HB and NB can be explained by the overall Comptonization COMPTB model, suggesting that the hard X-ray tails could have resulted from the Comptonization of the photons from the neutron star (NS) surface by the thermal electrons in the region between the NS and the disk and the energetic electrons in the freefall toward the NS in the converging flow onto the NS. However, this model cannot be responsible for the hard X-ray tails in the FB. Further study on the FB hard X-ray tails is needed. [ABSTRACT FROM AUTHOR]

Fast X-ray Transients (FXTs) are X-ray flares with durations ranging from a few hundred seconds to a few hours. Possible origins include the tidal disruption of a white dwarf by an intermediate-mass black hole, a supernova shock breakout, or a binary neutron star merger. We present the X-ray light curve and spectrum as well as deep optical imaging of the FXT XRT 210423, which has been suggested to be powered by a magnetar produced in a binary neutron star merger. Our Very Large Telescope and Gran Telescopio Canarias (GTC) observations began on 2021 May 6, thirteen days after the onset of the flare. No transient optical counterpart is found in the 1.″ (3 σ) X-ray uncertainty region of the source to a depth g s = 27.0 AB mag. (We use the word "counterpart" for any transient light in a wave band other than the original X-ray detection wave band, whereas the word "host" refers to the host galaxy.) A candidate host lies within the 1.″ X-ray uncertainty region with a magnitude of 25.9 ± 0.1 in the GTC/HiPERCAM g s filter. Due to its faintness, it was not detected in other bands, precluding a photometric redshift determination. We detect two additional candidate host galaxies: one with z spec = 1.5082 ± 0.0001 and an offset of 4.″2 ± 1.″ (37 ± 9 kpc) from the FXT, and another one with z phot = 1.04 − 0.14 + 0.22 and an offset of 3.″6 ± 1.″ (30 ± 8 kpc). Based on the properties of all the prospective hosts, we favor a binary neutron star merger, as previously suggested in the literature, as the explanation for XRT 210423. [ABSTRACT FROM AUTHOR]

We present 18 yr of OGLE photometry together with spectra obtained over 12 yr revealing that the early Oe star AzV 493 shows strong photometric (Δ I < 1.2 mag) and spectroscopic variability with a dominant, 14.6 yr pattern and ∼40 day oscillations. We estimate the stellar parameters T eff = 42,000 K, log L / L ⊙ = 5.83 ± 0.15 , M / M ⊙ = 50 ± 9, and v sin i = 370 ± 40 km s−1. Direct spectroscopic evidence shows episodes of both gas ejection and infall. There is no X-ray detection, and it is likely a runaway star. The star AzV 493 may have an unseen companion on a highly eccentric (e > 0.93) orbit. We propose that close interaction at periastron excites ejection of the decretion disk, whose variable emission-line spectrum suggests separate inner and outer components, with an optically thick outer component obscuring both the stellar photosphere and the emission-line spectrum of the inner disk at early phases in the photometric cycle. It is plausible that AzV 493's mass and rotation have been enhanced by binary interaction followed by the core-collapse supernova explosion of the companion, which now could be either a black hole or a neutron star. This system in the Small Magellanic Cloud can potentially shed light on OBe decretion disk formation and evolution, massive binary evolution, and compact binary progenitors. [ABSTRACT FROM AUTHOR]

The rapid increase in serendipitous X-ray source detections requires the development of novel approaches to efficiently explore the nature of X-ray sources. If even a fraction of these sources could be reliably classified, it would enable population studies for various astrophysical source types on a much larger scale than currently possible. Classification of large numbers of sources from multiple classes characterized by multiple properties (features) must be done automatically and supervised machine learning (ML) seems to provide the only feasible approach. We perform classification of Chandra Source Catalog version 2.0 (CSCv2) sources to explore the potential of the ML approach and identify various biases, limitations, and bottlenecks that present themselves in these kinds of studies. We establish the framework and present a flexible and expandable Python pipeline, which can be used and improved by others. We also release the training data set of 2941 X-ray sources with confidently established classes. In addition to providing probabilistic classifications of 66,369 CSCv2 sources (21% of the entire CSCv2 catalog), we perform several narrower-focused case studies (high-mass X-ray binary candidates and X-ray sources within the extent of the H.E.S.S. TeV sources) to demonstrate some possible applications of our ML approach. We also discuss future possible modifications of the presented pipeline, which are expected to lead to substantial improvements in classification confidences. [ABSTRACT FROM AUTHOR]

We make the first observation-based calculation of the energy that goes into cosmic ray protons versus cosmic ray electrons in shock acceleration during structure formation. We find a ratio of energy in cosmic ray protons to energy in cosmic ray electrons of 0.86. This value, calculated from the nonthermal X-ray component reported here from RTXE and the Fermi LAT upper limit for gamma-ray emission, is significantly lower than theoretical estimates that place most of the nonthermal energy in protons. Our estimate is based on the detection of nonthermal X-ray emission using the 3â€"20 keV RXTE spectrum, which shows residual emission not well modeled by a single thermal component. The statistical significance of adding a nonthermal, power-law component is 96%. The significance of adding a second thermal component is 90%. The addition of a component consisting of full cosmic X-ray background fluctuation to an isothermal model is significant with 92% confidence. The cumulative probability for the two-thermal-component model is 81% and 90% for the thermal plus power law. Thus the model with nonthermal emission is the preferred description of the data. Evidence of shock heating between the clusters in the spectro-imaging data of XMM, Chandra, and Suzaku indicates that a cosmic ray component should also be present and supports a nonthermal interpretation for the additional component. The bolometric nonthermal X-ray luminosity is 1.6 Ă— 1044 ergs sâˆ'1, 36% of the total X-ray emission in the 0.1â€"100 keV band. [ABSTRACT FROM AUTHOR]

We present observations of ASASSN-20hx, a nearby ambiguous nuclear transient (ANT) discovered in NGC 6297 by the All-Sky Automated Survey for Supernovae (ASAS-SN). We observed ASASSN-20hx from âˆ'30 to 275 days relative to the peak UV/optical emission using high-cadence, multiwavelength spectroscopy and photometry. From Transiting Exoplanet Survey Satellite data, we determine that the ANT began to brighten on 2020 June 22.8 with a linear rise in flux for at least the first week. ASASSN-20hx peaked in the UV/optical 30 days later on 2020 July 22.8 (MJD = 59052.8) at a bolometric luminosity of L = (3.15 ± 0.04) Ă— 1043 erg sâˆ'1. The subsequent decline is slower than any TDE observed to date and consistent with many other ANTs. Compared to an archival X-ray detection, the X-ray luminosity of ASASSN-20hx increased by an order of magnitude to L x ∼ 1.5 Ă— 1042 erg sâˆ'1 and then slowly declined over time. The X-ray emission is well fit by a power law with a photon index of Î" ∼ 2.3â€"2.6. Both the optical and near-infrared spectra of ASASSN-20hx lack emission lines, unusual for any known class of nuclear transient. While ASASSN-20hx has some characteristics seen in both tidal disruption events and active galactic nuclei, it cannot be definitively classified with current data. [ABSTRACT FROM AUTHOR]

Progenitors of core-collapse supernovae (SNe) can shed significant mass to circumstellar material (CSM) in the months to years preceding core collapse. The ensuing SN explosion launches ejecta that may subsequently collide with this CSM, producing shocks that can power emissions across the electromagnetic spectrum. In this work we explore the thermal signatures of dense CSM interaction when the CSM density profile is truncated at some outer radius. CSM with optical depth > c/v (where v is the shock velocity) will produce primarily ∼blackbody optical/UV emission, whereas lower optical depth CSM will power bremsstrahlung X-ray emission. Focusing on the latter, we derive light curves and spectra of the resulting X-ray transients that include a detailed treatment of Comptonization. Due to strong photoelectric absorption, the X-ray light curve is dominated by the postinteraction phase that occurs after the shock reaches the CSM truncation radius. We treat this regime here for the first time. Using these results, we present the phase space of optical, UV, and X-ray transients as a function of CSM properties, and discuss detectability prospects. We find that ROSAT would not have been sensitive to CSM X-ray transients but that eROSITA is expected to detect many such events. Future wide-field UV missions such as the Ultraviolet Transient Astronomy Satellite will dramatically enhance sensitivity to large optical depth CSM configurations. Finally, we present a framework within which CSM properties may be directly inferred from observable features of X-ray transients. This can serve as an important tool for studying stellar mass loss using SN X-ray detections. [ABSTRACT FROM AUTHOR]

Intermediate-mass black holes (IMBHs) by definition have masses of MIMBH ∼ 102−5M⊙, a range with few observational constraints. Finding IMBHs in globular star clusters (GCs) would validate a formation channel for massive black-hole seeds in the early universe. Here, we simulate a 60 hr observation with the next-generation Very Large Array (ngVLA) of 728 GC candidates in the Virgo Cluster galaxy NGC 4472. Interpreting the radio detection thresholds as signatures of accretion onto IMBHs, we benchmark IMBH mass thresholds in three scenarios and find the following: (1) radio analogs of ESO 243-49 HLX-1, a strong IMBH candidate with in a star cluster, are easy to access in all 728 GC candidates. (2) For the 30 GC candidates with extant X-ray detections, the empirical fundamental-plane relation involving black-hole mass plus X-ray and radio luminosities suggests access to , with an uncertainty of 0.44 dex. (3) A fiducial Bondi accretion model was applied to all 728 GC candidates and to radio stacks of the GC candidates. This model suggests access to IMBH masses, with a statistical uncertainty of 0.39 dex, of for individual GC candidates, and for radio stacks of about 100–200 GC candidates. The fiducial Bondi model offers initial guidance, but is subject to additional systematic uncertainties and should be superseded by hydrodynamical simulations of gas flows in GCs. [ABSTRACT FROM AUTHOR]

Previous detections of an X-ray emission line near 3.5 keV in galaxy clusters and other dark-matter-dominated objects have been interpreted as observational evidence for the decay of sterile neutrino dark matter. Motivated by this, we report on a search for a 3.5 keV emission line from the Milky Way's galactic dark matter halo with HaloSat. As a single pixel, collimated instrument, HaloSat observations are impervious to potential systematic effects due to grazing incidence reflection and CCD pixelization, and thus may offer a check on possible instrumental systematic errors in previous analyses. We report nondetections of a ∼3.5 keV emission line in four HaloSat observations near the Galactic center. In the context of the sterile neutrino decay interpretation of the putative line feature, we provide 90% confidence level upper limits on the 3.5 keV line flux for a field centered 18.6 degrees from the Galactic center and the corresponding 7.1 keV sterile neutrino mixing angle: F ≤ 0.077 ph cm−2 s−1 sr−1 and. The HaloSat mixing angle upper limit was calculated using a modern parameterization of the Milky Way's dark matter distribution, and in order to compare with previous limits, we also report the limit calculated using a common historical model. The HaloSat mixing angle upper limit places constraints on a number of previous mixing angle estimates derived from observations of the Milky Way's dark matter halo and galaxy clusters, and excludes several previous detections of the line. The upper limits cannot, however, entirely rule out the sterile neutrino decay interpretation of the 3.5 keV line feature. [ABSTRACT FROM AUTHOR]

The translucent GGAG:Ce/glass composites are prepared successfully by ball-milling, tableting, and pressureless sintering. The thickness of composites is about 400 μm. The x-ray diffraction (XRD), differential scanning calorimetry (DSC), density of composite materials are measured and discussed systematically. The scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS) elemental mapping are employed to analyze the particle size, the shape of powders, and the distribution of GGAG:Ce particles in the glass matrix, respectively. The decay time, ultraviolet, (UV), x-ray excitation luminescence spectra, and temperature spectra are studied. The results show that the composite materials have high light output, good thermostability, and short decay time. The method adopted in this work is an effective method to reduce the preparation time and cost of the sample. The ultralow afterglow indicates that the composite materials have an opportunity to be used for x-ray detection and imaging. [ABSTRACT FROM AUTHOR]

Spectral computed tomography has great potential for multi-energy imaging and anti-artifacts. The complete absorption-based energy resolving scheme of x-rays has been used for the integrity of detected information. However, this scheme is limited by the fact that the detector pixel thickness is high and fixed. Here, an energy resolving scheme is proposed using the crosstalk correction method for the incomplete absorption detection of x-rays. A fully connected neural network (FCNN)-based method was used to correct the difference caused by internal x-ray crosstalk of the edge-on detector. The energy and spatial features of the data which is collected in layers were combined to establish the mapping between the ideal data and the data with crosstalk at the pre-processing stage. Thereafter, to reconstruct the stable and highly accurate energy-resolving equations, the layers with low relative energy difference were selected and grouped together to reduce the accumulation difference. The experiment results demonstrate the feasibility of this energy resolving scheme. The differences caused by crosstalk can be suppressed through the proposed FCNN-based method. The resolving accuracy can be further improved by grouping more layers at forward positions in the pixel. Moreover, this improvement can be observed in the reconstructed images with reduced artifacts and improved quality. [ABSTRACT FROM AUTHOR]