Showing papers on "Synchrotron radiation published in 2018"
TL;DR: In this paper, the authors present numerical simulations of energetic flows propagating through the debris cloud of a binary neutron star (BNS) merger, and compare two distinct models for the central engine, referred to as the narrow and wide engine scenario, which is associated with a successful structured jet and a quasi-isotropic explosion respectively.
Abstract: We present numerical simulations of energetic flows propagating through the debris cloud of a binary neutron star (BNS) merger. Starting from the scale of the central engine, we use a moving-mesh hydrodynamics code to simulate the complete dynamical evolution of the produced relativistic jets. We compute synchrotron emission directly from the simulations and present multi-band light curves of the early (sub-day) through late (weeks to years) afterglow stages. Our work systematically compares two distinct models for the central engine, referred to as the narrow and wide engine scenario, which is associated with a successful structured jet and a quasi-isotropic explosion respectively. Both engine models naturally evolve angular and radial structure through hydrodynamical interaction with the merger debris cloud. They both also result in a relativistic blast wave capable of producing the observed multi-band afterglow data. However, we find that the narrow and wide engine scenario might be differentiated by a new emission component that we refer to as a merger flash. This component is a consequence of applying the synchrotron radiation model to the shocked optically thin merger cloud. Such modeling is appropriate if injection of non-thermal electrons is sustained in the breakout relativistic shell, for example by internal shocks or magnetic reconnection. The rapidly declining signature may be detectable for future BNS mergers during the first minutes to day following the GW chirp. Furthermore, its non-detection for the GRB170817A event may disfavor the wide, quasi-isotropic explosion model.
115 citations
TL;DR: A laboratory-scale LPBF test bed designed to accommodate diffraction and imaging experiments at a synchrotron X-ray source during LPBF operation is described and experimental results using Ti-6Al-4V, a widely used aerospace alloy, as a model system are presented.
Abstract: In situ X-ray-based measurements of the laser powder bed fusion (LPBF) additive manufacturing process produce unique data for model validation and improved process understanding. Synchrotron X-ray imaging and diffraction provide high resolution, bulk sensitive information with sufficient sampling rates to probe melt pool dynamics as well as phase and microstructure evolution. Here, we describe a laboratory-scale LPBF test bed designed to accommodate diffraction and imaging experiments at a synchrotron X-ray source during LPBF operation. We also present experimental results using Ti-6Al-4V, a widely used aerospace alloy, as a model system. Both imaging and diffraction experiments were carried out at the Stanford Synchrotron Radiation Lightsource. Melt pool dynamics were imaged at frame rates up to 4 kHz with a ∼1.1 μm effective pixel size and revealed the formation of keyhole pores along the melt track due to vapor recoil forces. Diffraction experiments at sampling rates of 1 kHz captured phase evolution and lattice contraction during the rapid cooling present in LPBF within a ∼50 × 100 μm area. We also discuss the utility of these measurements for model validation and process improvement.
113 citations
TL;DR: In this paper, the authors performed time-resolved gamma-ray spectroscopy of single-peaked GRBs as measured with Fermi/GBM and demonstrated that idealized synchrotron emission, when properly incorporating time-dependent cooling of the electrons, is capable of fitting ~95% of all these GBM spectra.
Abstract: Gamma-ray bursts are the most energetic electromagnetic sources in the Universe. Their prompt gamma-ray radiation corresponds to an energy release of 1E42-1E47J. Fifty years after their discovery and several dedicated space-based instruments, the physical origin of this emission is still unknown. Synchrotron emission has been one of the early contenders but was criticized because spectral fits of empirical models (such as a smoothly-connected broken power law or a cut-off power law) suggest too hard a slope of the low-energy power law, violating the so-called synchrotron line-of-death. We perform time-resolved gamma-ray spectroscopy of single-peaked GRBs as measured with Fermi/GBM. We demonstrate that idealized synchrotron emission, when properly incorporating time-dependent cooling of the electrons, is capable of fitting ~95% of all these GBM spectra. The comparison with spectral fit results based on previous empirical models demonstrates that the past exclusion of synchrotron radiation as an emission mechanism derived via the line-of-death was misleading. Our analysis probes the physics of these ultra-relativistic outflows and the related microphysical processes, and for the first time provides estimates of magnetic field strength and Lorentz factors of the emitting region directly from spectral fits. Our modeling of the Fermi/GBM observations provides evidence that GRBs are produced by moderately magnetized jets in which relativistic mini-jets emit optically-thin synchrotron radiation at large emission radii.
82 citations
15 Feb 2018
TL;DR: In this paper, the authors compared malignant human cancer cells and tissues before and after irradiating of synchrotron radiation using Saturated Spectroscopy and Unsaturated Spectrograms, respectively.
Abstract: In the current study, we have experimentally and comparatively investigated and compared malignant human cancer cells and tissues before and after irradiating of synchrotron radiation using Saturated Spectroscopy and Unsaturated Spectroscopy, respectively.
71 citations
07 Feb 2018
TL;DR: In this paper, the authors have experimentally and comparatively investigated and compared malignant human cancer cells and tissues before and after irradiating of white and monochromatic synchrotron radiation using Vibrational Circular Dichroism Spectroscopy and video spectroscopy, respectively.
Abstract: In the current study, we have experimentally and comparatively investigated and compared malignant human cancer cells and tissues before and after irradiating of white and monochromatic synchrotron radiation using Vibrational Circular Dichroism Spectroscopy and Video Spectroscopy, respectively. It is clear that malignant human cancer cells and tissues have gradually transformed to benign human cancer cells and tissues under white and monochromatic synchrotron radiation with the passage of time (Figures 1-4) [1-108]. Clinical Image
71 citations
01 Jan 2018
TL;DR: In this paper, the authors experimentally and comparatively investigated and compared malignant human cancer cells and tissues before and after irradiating of synchrotron radiation using Nuclear Resonant Inelastic X-Ray Scattering Spectroscopy (NRIXSS) and Nuclear Resonance Vibrational Spectrograms (NRVS).
Abstract: In the current study, we have experimentally and comparatively investigated and compared malignant human cancer cells and tissues before and after irradiating of synchrotron radiation using Nuclear Resonant Inelastic X–Ray Scattering Spectroscopy (NRIXSS) and Nuclear Resonance Vibrational Spectroscopy (NRVS). It is clear that malignant human cancer cells and tissues have gradually transformed to benign human cancer cells and tissues under synchrotron radiation with the passing of time (Figures 1 and 2) [1-182].
69 citations
20 Apr 2018
TL;DR: In this article, the authors demonstrate that fiber-based supercontinuum sources in the mid-infrared enable fast spectral mapping of localized material properties with close to diffraction-limited resolution.
Abstract: Fourier-transform infrared (FTIR) spectromicroscopy combines the spatial resolution of optical microscopy with the spectral selectivity of vibrational spectroscopy. Synchrotron sources can provide diffraction-limited beams in the infrared, and therefore synchrotron-based FTIR spectromicroscopy is nowadays an indispensable tool for biology and materials science studies where high spatial resolution is required. However, the increasing need for accurate and highly spatially resolved characterization is calling for alternative laboratory-based sources to complement synchrotron radiation. To date, the low brightness of thermal emitters or high temporal coherence and narrow bandwidth or tunability of laser sources have hindered the progress of bench-top FTIR spectromicroscopy. Here, we demonstrate that fiber-based supercontinuum sources in the mid-infrared enable fast spectral mapping of localized material properties with close to diffraction-limited resolution (3 μm×3 μm) and pave the way to table-top, on-demand, fast, and highly spatially resolved studies. We illustrate these capabilities by imaging thin sections of human liver samples and compare the results and performance with those obtained using a synchrotron source.
66 citations
TL;DR: An end-station for resonant inelastic X-ray scattering and (resonant) X-rays emission spectroscopy at beamline ID20 of ESRF - The European Synchrotron is presented.
Abstract: An end-station for resonant inelastic X-ray scattering and (resonant) X-ray emission spectroscopy at beamline ID20 of ESRF - The European Synchrotron is presented. The spectrometer hosts five crystal analysers in Rowland geometry for large solid angle collection and is mounted on a rotatable arm for scattering in both the horizontal and vertical planes. The spectrometer is optimized for high-energy-resolution applications, including partial fluorescence yield or high-energy-resolution fluorescence detected X-ray absorption spectroscopy and the study of elementary electronic excitations in solids. In addition, it can be used for non-resonant inelastic X-ray scattering measurements of valence electron excitations.
66 citations
01 Mar 2018
TL;DR: In this article, the authors have experimentally and comparatively investigated and compared malignant human cancer cells and tissues before and after irradiating of synchrotron radiation using Small-Angle Neutron Scattering (SANS) and Wide Angle X-Ray Diffraction (WAXD).
Abstract: In the current study, we have experimentally and comparatively investigated and compared malignant human cancer cells and tissues before and after irradiating of synchrotron radiation using Small-Angle Neutron Scattering (SANS) and Wide-Angle X-Ray Diffraction (WAXD), It is clear that malignant human cancer cells and tissues have gradually transformed to benign human cancer cells and tissues under synchrotron radiation with the passing of time (Figures 1 and 2) [1-135].
65 citations
01 Jun 2018
64 citations
01 Jan 2018
TL;DR: In this paper, the authors have experimentally and comparatively investigated and compared malignant human cancer cells and tissues before and after irradiating of synchrotron radiation using fluctuation X-ray scattering (FXS) and Wide Angle X-Ray Scattering (WAXS).
Abstract: Received: August 02, 2018; Accepted: August 17, 2018; Published: August 20, 2018 In the current study, we have experimentally and comparatively investigated and compared malignant human cancer cells and tissues before and after irradiating of synchrotron radiation using Fluctuation X–Ray Scattering (FXS) and Wide–Angle X–Ray Scattering (WAXS). It is clear that malignant human cancer cells and tissues have gradually transformed to benign human cancer cells and tissues under synchrotron radiation with the passing of time (Figures 1 and 2) [1182].
TL;DR: In this paper, the beam longitudinal and transverse phase-space of the presently available LWFA beams are manipulated using variable strength quadrupoles, and the useful energy range passing through a slit in a magnetic chicane is selected.
Abstract: With gigaelectron-volts per centimetre energy gains and femtosecond electron beams, laser wakefield acceleration (LWFA) is a promising candidate for applications, such as ultrafast electron diffraction, multistaged colliders and radiation sources (betatron, compton, undulator, free electron laser). However, for some of these applications, the beam performance, for example, energy spread, divergence and shot-to-shot fluctuations, need a drastic improvement. Here, we show that, using a dedicated transport line, we can mitigate these initial weaknesses. We demonstrate that we can manipulate the beam longitudinal and transverse phase-space of the presently available LWFA beams. Indeed, we separately correct orbit mis-steerings and minimise dispersion thanks to specially designed variable strength quadrupoles, and select the useful energy range passing through a slit in a magnetic chicane. Therefore, this matched electron beam leads to the successful observation of undulator synchrotron radiation after an 8 m transport path. These results pave the way to applications demanding in terms of beam quality.
29 Jan 2018
TL;DR: It is clear that malignant human cancers’ cells, tissue and tumors have gradually transformed to benign human cancers' cells, tissues and tumors under synchrotron radiation with the passage of time.
Abstract: In the current study, we have experimentally and comparatively investigated and compared malignant human common cancers’ cells, tissues and tumors such as Bladder Cancer, Breast Cancer, Colon and Rectal Cancer, Endometrial Cancer, Kidney Cancer, Leukemia, Liver, Lung Cancer, Melanoma, Non–Hodgkin Lymphoma, Pancreatic Cancer, Prostate Cancer and Thyroid Cancer before and after irradiating of synchrotron radiation therapy process using some modern biospectroscopic techniques and methods. It is clear that malignant human cancers’ cells, tissues and tumors have gradually transformed to benign human cancers’ cells, tissues and tumors under synchrotron radiation with the passage of time (Figures 1-13) [1–123].
01 Jan 2018
TL;DR: In this article, the authors have experimentally and comparatively investigated and compared malignant human cancer cells and tissues before and after irradiating of synchrotron radiation using Small Angle X-Ray Scattering (SAXS) and USAXS.
Abstract: In the current study, we have experimentally and comparatively investigated and compared malignant human cancer cells and tissues before and after irradiating of synchrotron radiation using Small–Angle X–Ray Scattering (SAXS) and Ultra–Small Angle X–Ray Scattering (USAXS). It is clear that malignant human cancer cells and tissues have gradually transformed to benign human cancer cells and tissues under synchrotron radiation with the passing of time (Figures 1 and 2) [1182].
01 Jan 2018
TL;DR: In this paper, the authors show that synchrotron radiation causes progressive changes to the XANES spectra of hydrous glasses as a function of radiation dose (here defined as total photons delivered per square micrometer), water concentration and initial Fe3+/ΣFe ratio.
Abstract: Abstract Oxygen fugacity (fo2) exerts first-order control on the geochemical evolution of planetary interiors, and the Fe3+/ΣFe ratios of silicate glasses provide a useful proxy for fO2. Fe K-edge micro-X-ray absorption near-edge structure (XANES) spectroscopy allows researchers to micro-analytically determine the Fe3+/ΣFe ratios of silicate glasses with high precision. In this study we characterize hydrous and anhydrous basalt glass standards with Mössbauer and XANES spectroscopy and show that synchrotron radiation causes progressive changes to the XANES spectra of hydrous glasses as a function of radiation dose (here defined as total photons delivered per square micrometer), water concentration, and initial Fe3+/ΣFe ratio. We report experiments from eight different radiation dose conditions and show that Fe in hydrous silicate glasses can undergo rapid oxidation upon exposure to radiation. The rate and degree of oxidation correlates with radiation dose and the product of water concentration and ferrous/ferric iron oxide ratio on a molar basis (Φ = XHO0.5·XFeO/XFeO1.5). For example, a basalt glass with 4.9 wt% dissolved H2O and Fe3+/ΣFe = 0.19 from its Mössbauer spectrum may appear to have Fe3+/ΣFe ≥ 0.35 when analyzed over several minutes at a nominal flux density of ~2 × 109 photons/s/μm2. This radiation-induced increase in Fe3+/ΣFe ratio would lead to overestimation of fO2 by about two orders of magnitude, with dramatic consequences for the interpretation of geological processes. The sample area exposed to radiation shows measureable hydrogen loss, consistent with radiation-induced breaking of O–H bonds, associated H migration and loss, and oxidation of Fe2+. This mechanism is consistent with the observation that anhydrous glasses show no damage under any beam conditions. Cryogenic cooling does not mitigate, but rather accelerates, iron oxidation. The effects of beam damage appear to persist indefinitely. We detect beam damage at the lowest photon flux densities tested (3 × 106 photons/s/ μm2); however, at flux densities ≤6 × 107 photons/s/µm2, the hydrous glass calibration curve defined by the centroid (derived from XANES spectra) and Fe3+/SFe ratios (derived from Mössbauer spectra) is indistinguishable from the anhydrous calibration curve within the accuracy achievable with Mössbauer spectroscopy. Thus, published Fe3+/ΣFe ratios from hydrous glasses measured at low photon flux densities are likely to be accurate within measurement uncertainty with respect to what would have been measured by Mössbauer spectroscopy. These new results demonstrate that to obtain accurate Fe3+/ΣFe ratios from hydrous, mafic, silicate glasses, it is first necessary to carefully monitor changes in the XANES spectra as a function of incident dose (e.g., fixed-energy scan). Defocusing and attenuating the beam may prevent significant oxidation of Fe in mafic water-bearing glasses.
TL;DR: In this article, a relativistic radiative transfer calculation of the emitted synchrotron radiation was performed to obtain polarized images for a range of mass accretion rates and electron temperatures.
Abstract: We study model images and polarization maps of Sagittarius A* at 230 GHz. We post-process GRMHD simulations and perform a fully relativistic radiative transfer calculation of the emitted synchrotron radiation to obtain polarized images for a range of mass accretion rates and electron temperatures. At low accretion rates, the polarization map traces the underlying toroidal magnetic field geometry. At high accretion rates, we find that Faraday rotation internal to the emission region can depolarize and scramble the map. We measure the net linear polarization fraction and find that high accretion rate "jet-disc" models are heavily depolarized and are therefore disfavoured. We show how Event Horizon Telescope measurements of the polarized "correlation length" over the image provide a model-independent upper limit on the strength of these Faraday effects, and constrain plasma properties like the electron temperature and magnetic field strength.
TL;DR: The Heidelberg Compact EBIT (HC-EBIT) as discussed by the authors is a compact, room-temperature design for electron beam ion traps that can trap and extract highly charged ions.
Abstract: Electron beam ion traps (EBITs) are ideal tools for both production and study of highly charged ions (HCIs). In order to reduce their construction, maintenance, and operation costs, we have developed a novel, compact, room-temperature design, the Heidelberg Compact EBIT (HC-EBIT). Four already commissioned devices operate at the strongest fields (up to 0.86 T) reported for such EBITs using permanent magnets, run electron beam currents up to 80 mA, and energies up to 10 keV. They demonstrate HCI production, trapping, and extraction of pulsed Ar16+ bunches and continuous 100 pA ion beams of highly charged Xe up to charge state 29+, already with a 4 mA, 2 keV electron beam. Moreover, HC-EBITs offer large solid-angle ports and thus high photon count rates, e.g., in x-ray spectroscopy of dielectronic recombination in HCIs up to Fe24+, achieving an electron-energy resolving power of E/ΔE > 1500 at 5 keV. Besides traditional on-axis electron guns, we have also implemented a novel off-axis gun for laser, synchrotron, and free-electron laser applications, offering clear optical access along the trap axis. We report on its first operation at a synchrotron radiation facility demonstrating the resonant photoexcitation of highly charged oxygen.
TL;DR: In this article, a semi-analytical model of electron-positron cascades was developed to simulate pair cascades with an arbitrary number of microphysical processes and use it to explore cascade properties for a wide range of pulsar parameters.
Abstract: We study electron-positron pair production in polar caps of energetic pulsars to determine the maximum multiplicity of pair plasma a pulsar can produce under the most favorable conditions. This paper complements and updates our study of pair cascades presented in Timokhin & Harding (2015) with more accurate treatment of the effects of ultra strong B>3x10^{12}G magnetic fields and emission processes of primary and secondary particles. We include pairs produced by curvature and synchrotron radiation photons as well as resonant Compton scattered photons. We develop a semi-analytical model of electron-positrons cascades which can efficiently simulate pair cascades with an arbitrary number of microphysical processes and use it to explore cascade properties for a wide range of pulsar parameters. We argue that the maximum cascade multiplicity can not exceed ~ a few x 10^5 and the multiplicity has a rather weak dependence on pulsar period on pulsar period. The highest multiplicity is achieved in pulsars with magnetic field 4x10^{12} 10^6K. We also derive analytical expressions for several physical quantities relevant for electromagnetic cascade in pulsars which may be useful in future works on pulsar cascades, including the upper limit on cascade multiplicity and various approximations for the parameter \chi, the exponential factor in the expression for photon attenuation in strong magnetic field.
TL;DR: In this article, the authors demonstrate the advantages of in situ synchrotron radiation X-ray scattering, Xray nano-CT and infrared imaging in the study of deformation-induced multi-scale structural evolutions of polymers with time resolution up to sub-ms.
Abstract: Synchrotron radiation (SR) provides highly brilliant light with tunable wavelength from hard X-ray to far infrared, on which scattering, spectroscopy and imaging techniques with high time and spatial resolutions have been developed for in situ study on biological system and materials like polymer With examples on flow-induced crystallization of polymer, deformation of nanoparticle filler network in rubber composite and necking propagation in tensile stretch, current work attempts to demonstrate the advantages of in situ synchrotron radiation X-ray scattering, X-ray nano-CT and infrared imaging in the study of deformation-induced multi-scale structural evolutions of polymers With time resolution up to sub-ms, synchrotron radiation is expected to play a great role in understanding non-equilibrium polymer physics under processing and service conditions, while high-throughput characterization platform based on synchrotron radiation opens the possibility to establish polymer Materials Genome database in processing parameter space within reasonable time, which can serve as the roadmap for industrial polymer processing and accelerate material innovation
TL;DR: Combining a homemade film blowing machine and an in situ synchrotron radiation source with small and wide-angle X-ray scattering (SAXS and WAXS) capability, an investigation of film blowing of pol...
Abstract: Combining a homemade film blowing machine and an in situ synchrotron radiation source with small- and wide-angle X-ray scattering (SAXS and WAXS) capability, an investigation of film blowing of pol...
TL;DR: In this article, emission signatures of binary compact star gravitational wave sources consisting of strongly magnetized neutron stars and/or white dwarfs (WDs) in their late-time inspiral phase were investigated.
Abstract: We investigate emission signatures of binary compact star gravitational wave sources consisting of strongly magnetized neutron stars (NSs) and/or white dwarfs (WDs) in their late-time inspiral phase. Because of electromagnetic interactions between the magnetospheres of the two compact stars, a substantial amount of energy will be extracted, and the resultant power is expected to be $\sim 10^{38} - 10^{44}$ erg/s in the last few seconds before the two stars merge, when the binary system contains a NS with a surface magnetic field $10^{12}$ G. The induced electric field in the process can accelerate charged particles up to the EeV energy range. Synchrotron radiation is emitted from energetic electrons, with radiative energies reaching the GeV energy for binary NSs and the MeV energy for NS - WD or double WD binaries. In addition, a blackbody component is also presented and it peaks at several to hundreds keV for binary NSs and at several keV for NS - WD or double WD binaries. The strong angular dependence of the synchrotron radiation and the isotropic nature of the blackbody radiation lead to distinguishable modulation patterns between the two emission components. If coherent curvature radiation is presented, fast radio bursts could be produced. These components provide unique simultaneous electromagnetic signatures as precursors of gravitational wave events associated with magnetized compact star mergers and short gamma ray bursts (e.g., GRB 100717).
TL;DR: In this article, the authors use test particle simulations, tracing the propagation of charged particles (protons) through a random magnetic field, to study the cosmic ray distribution at scales comparable to the correlation scale of the turbulent flow in the interstellar medium.
Abstract: Synchrotron radiation from cosmic rays is a key observational probe of the galactic magnetic field. Interpreting synchrotron emission data requires knowledge of the cosmic ray number density, which is often assumed to be in energy equipartition (or otherwise tightly correlated) with the magnetic field energy. However, there is no compelling observational or theoretical reason to expect such tight correlation to hold across all scales. We use test particle simulations, tracing the propagation of charged particles (protons) through a random magnetic field, to study the cosmic ray distribution at scales comparable to the correlation scale of the turbulent flow in the interstellar medium ($\simeq 100\,{\rm pc}$ in spiral galaxies). In these simulations, we find that there is no spatial correlation between the cosmic ray number density and the magnetic field energy density. In fact, their distributions are approximately statistically independent. We find that low-energy cosmic rays can become trapped between magnetic mirrors, whose location depends more on the structure of the field lines than on the field strength.
TL;DR: In this article, the authors used the SOFT (Synchrotron-detecting Orbit Following Toolkit) to simulate synchrotor images and spectra using Fokker-Planck simulations for parameters from an Alcator C-Mod discharge.
Abstract: Improved understanding of the dynamics of runaway electrons can be obtained by measurement and interpretation of their synchrotron radiation emission. Models for synchrotron radiation emitted by relativistic electrons are well established, but the question of how various geometric effects -- such as magnetic field inhomogeneity and camera placement -- influence the synchrotron measurements and their interpretation remains open. In this paper we address this issue by simulating synchrotron images and spectra using the new synthetic synchrotron diagnostic tool SOFT (Synchrotron-detecting Orbit Following Toolkit). We identify the key parameters influencing the synchrotron radiation spot and present scans in those parameters. Using a runaway electron distribution function obtained by Fokker-Planck simulations for parameters from an Alcator C-Mod discharge, we demonstrate that the corresponding synchrotron image is well-reproduced by SOFT simulations, and we explain how it can be understood in terms of the parameter scans. Geometric effects are shown to significantly influence the synchrotron spectrum, and we show that inherent inconsistencies in a simple emission model (i.e. not modeling detection) can lead to incorrect interpretation of the images.
TL;DR: In this paper, emission signatures of binary compact star gravitational wave (GW) sources consisting of strongly magnetized neutron stars (NSs) and/or white dwarfs (WDs) in their late-time inspiral phase were investigated.
Abstract: We investigate emission signatures of binary compact star gravitational wave (GW) sources consisting of strongly magnetized neutron stars (NSs) and/or white dwarfs (WDs) in their late-time inspiral phase. Because of electromagnetic interactions between the magnetospheres of the two compact stars, a substantial amount of energy will be extracted, and the resultant power is expected to be ∼1038-1044 erg s-1 in the last few seconds before the two stars merge, when the binary system contains a NS with a surface magnetic field 1012 G. The induced electric field in the process can accelerate charged particles up to the EeV energy range. Synchrotron radiation is emitted from energetic electrons, with radiative energies reaching the GeV energy for binary NSs and the MeV energy for NS-WD or double WD binaries. In addition, a blackbody component is also presented, and it peaks at several to hundreds keV for binary NSs and at several keV for NS-WD or double WD binaries. The strong angular dependence of the synchrotron radiation and the isotropic nature of the blackbody radiation lead to distinguishable modulation patterns between the two emission components. If coherent curvature radiation is presented, fast radio bursts could be produced. These components provide unique simultaneous electromagnetic signatures as precursors of GW events associated with magnetized compact star mergers and short gamma-ray bursts (e.g., GRB 100717).
TL;DR: An ad hoc data pre-processing procedure has been developed for the PIXIRAD-8 CdTe single-photon-counting detector and the effectiveness of the pre- processing is demonstrated for phase-contrast CT images of a human breast specimen.
Abstract: Large-area CdTe single-photon-counting detectors are becoming more and more attractive in view of low-dose imaging applications due to their high efficiency, low intrinsic noise and absence of a scintillating screen which affects spatial resolution. At present, however, since the dimensions of a single sensor are small (typically a few cm2), multi-module architectures are needed to obtain a large field of view. This requires coping with inter-module gaps and with close-to-edge pixels, which generally show a non-optimal behavior. Moreover, high-Z detectors often show gain variations in time due to charge trapping: this effect is detrimental especially in computed tomography (CT) applications where a single tomographic image requires hundreds of projections continuously acquired in several seconds. This work has been carried out at the SYRMEP beamline of the Elettra synchrotron radiation facility (Trieste, Italy), in the framework of the SYRMA-3D project, which aims to perform the world's first breast-CT clinical study with synchrotron radiation. An ad hoc data pre-processing procedure has been developed for the PIXIRAD-8 CdTe single-photon-counting detector, comprising an array of eight 30.7 mm × 24.8 mm modules tiling a 246 mm × 25 mm sensitive area, which covers the full synchrotron radiation beam. The procedure consists of five building blocks, namely dynamic flat-fielding, gap seaming, dynamic ring removal, projection despeckling and around-gap equalization. Each block is discussed and compared, when existing, with conventional approaches. The effectiveness of the pre-processing is demonstrated for phase-contrast CT images of a human breast specimen. The dynamic nature of the proposed procedure, which provides corrections dependent upon the projection index, allows the effective removal of time-dependent artifacts, preserving the main image features including phase effects.
TL;DR: In this paper, the authors studied the evolution of a two-dimensional reconnecting current sheet in pair plasma and showed how the inflow of the secondary plasma, with multiplicities up to several hundred, reduces the effective magnetization of the current sheet, suppressing the acceleration and thus decreasing the high energy photon spectrum cutoff.
Abstract: High energy radiation from nonthermal particles accelerated in relativistic magnetic reconnection is thought to be important in many astrophysical systems, ranging from blazar jets and black hole accretion disk coronae to pulsars and magnetar flares. The presence of a substantial density of high energy photons ($>$MeV) in these systems can make two-photon pair production ($\gamma\gamma\to e^-e^+$) an additional source of plasma particles and can affect the radiative properties of these objects. We present the results of novel particle-in-cell simulations that track both the radiated synchrotron photons and the created pairs, with which we study the evolution of a two-dimensional reconnecting current sheet in pair plasma. Synchrotron radiation from accelerated particles in the current sheet produces hot secondary pairs in the upstream which are later advected into the current sheet where they are reaccelerated and produce more photons. In the optically thin regime, when most of the radiation is leaving the upstream unaffected, this process is self-regulating and depends only on the background magnetic field and the optical depth of photons to pair production. The extra plasma loading also affects the properties of reconnection. We study how the inflow of the secondary plasma, with multiplicities up to several hundred, reduces the effective magnetization of the plasma, suppressing the acceleration and thus decreasing the high energy photon spectrum cutoff. This offers an explanation for the weak dependence of the observed gamma-ray cutoff in pulsars on the magnetic field at the light cylinder.
TL;DR: In this paper, the nonthermal radiative properties of 18 pulsar wind nebulae (PWNe) were studied in the 1D leptonic model, and the dynamical and radiative evolution of a PWN in a nonradiative supernova remnant were self-consistently investigated in this model.
Abstract: Aims. The nonthermal radiative properties of 18 pulsar wind nebulae (PWNe) are studied in the 1D leptonic model.Methods. The dynamical and radiative evolution of a PWN in a nonradiative supernova remnant are self-consistently investigated in this model. The leptons (electrons/positrons) are injected with a broken power-law form, and nonthermal emission from a PWN is mainly produced by time-dependent relativistic leptons through synchrotron radiation and inverse Compton process. Results. Observed spectral energy distributions (SEDs) of all 18 PWNe are reproduced well, where the indexes of low-energy electron components lie in the range of 1.0–1.8 and those of high-energy electron components in the range of 2.1–3.1. Our results show that F X /F γ > 10 for young PWNe; 1 X /F γ ≤ 10 for evolved PWNe, except for G292.0+1.8; and F X /F γ ≤ 1 for mature/old PWNe, except for CTA 1. Moreover, most PWNe are particle-dominated. Statistical analysis for the sample of 14 PWNe further indicate that (1) not all pulsar parameters have correlations with electron injection parameters, but electron maximum energy and PWN magnetic field correlate with the magnetic field at the light cylinder, the potential difference at the polar cap, and the spin-down power; (2) the spin-down power positively correlates with radio, X-ray, bolometric, and synchrotron luminosities, but does not correlate with gamma-ray luminosity; (3) the spin-down power positively correlates with radio, X-ray, and γ -band surface brightness; and (4) the PWN radius and the PWN age negatively correlate with X-ray luminosity, the ratio of X-ray to gamma-ray luminosities, and the synchrotron luminosity.
TL;DR: In this paper, the authors used the Kinetic Orbit Runaway electron Code (KORC) to compute the full-orbit relativistic dynamics in prescribed electric and magnetic fields including radiation damping and collisions.
Abstract: Numerical simulations of runaway electrons (REs) with a particular emphasis on orbit dependent effects in 3-D magnetic fields are presented. The simulations were performed using the recently developed Kinetic Orbit Runaway electron Code (KORC) that computes the full-orbit relativistic dynamics in prescribed electric and magnetic fields including radiation damping and collisions. The two main problems of interest are synchrotron radiation and impurity-based RE dissipation. Synchrotron radiation is studied in axisymmetric fields and in 3-D magnetic configurations exhibiting magnetic islands and stochasticity. For passing particles in axisymmetric fields, neglecting orbit effects might underestimate or overestimate the total radiation power depending on the direction of the radial shift of the drift orbits. For trapped particles, the spatial distribution of synchrotron radiation exhibits localized “hot” spots at the tips of the banana orbits. In general, the radiation power per particle for trapped particles is higher than the power emitted by passing particles. The spatial distribution of synchrotron radiation in stochastic magnetic fields, obtained using the MHD code NIMROD, is strongly influenced by the presence of magnetic islands. 3-D magnetic fields also introduce a toroidal dependence on the synchrotron spectra, and neglecting orbit effects underestimates the total radiation power. In the presence of magnetic islands, the radiation damping of trapped particles is larger than the radiation damping of passing particles. Results modeling synchrotron emission by RE in DIII-D quiescent plasmas are also presented. The computation uses EFIT reconstructed magnetic fields and RE energy distributions fitted to the experimental measurements. Qualitative agreement is observed between the numerical simulations and the experiments for simplified RE pitch angle distributions. However, it is noted that to achieve quantitative agreement, it is necessary to use pitch angle distributions that depart from simplified 2-D Fokker-Planck equilibria. Finally, using the guiding center orbit model (KORC-GC), a preliminary study of pellet mitigated discharges in DIII-D is presented. The dependence of RE energy decay and current dissipation on initial energy and ionization levels of neon impurities is studied. The computed decay rates are within the range of experimental observations.
TL;DR: The studied sample, an extensively ball milled iron alloy powder, provides an ideal test case, as domain size broadening and strain broadening are of comparable size.
Abstract: Separation of size and strain effects on diffraction line profiles has been studied in a round robin involving laboratory instruments and synchrotron radiation beamlines operating with different radiation, optics, detectors and experimental configurations. The studied sample, an extensively ball milled iron alloy powder, provides an ideal test case, as domain size broadening and strain broadening are of comparable size. The high energy available at some synchrotron radiation beamlines provides the best conditions for an accurate analysis of the line profiles, as the size–strain separation clearly benefits from a large number of Bragg peaks in the pattern; high counts, reliable intensity values in low-absorption conditions, smooth background and data collection at different temperatures also support the possibility to include diffuse scattering in the analysis, for the most reliable assessment of the line broadening effect. However, results of the round robin show that good quality information on domain size distribution and microstrain can also be obtained using standard laboratory equipment, even when patterns include relatively few Bragg peaks, provided that the data are of good quality in terms of high counts and low and smooth background.