Characteristics Of X-ray Emission Research Articles

Temperature-dependent x-ray fluorescent response from thermographic phosphors under x-ray excitation

Phosphor thermometry has been successfully applied within several challenging environments. Typically, the thermographic phosphors are excited by an ultraviolet light source, and the temperature-dependent spectral or temporal response is measured. However, this is challenging or impossible in optically thick environments. In addition, emission from other sources (e.g., a flame) may interfere with the optical phosphor emission. A temperature dependent x-ray excitation/emission could alleviate these issues as x-rays could penetrate obscurants with no interference from flame luminosity. In addition, x-ray emission could allow for thermometry within solids while simultaneously x-ray imaging the structural evolution. In this study, select thermographic phosphors were excited via x-ray radiation, and their x-ray emission characteristics were measured at various temperatures. Several of the phosphors showed varying levels of temperature dependence with the strongest sensitivity occurring for YAG:Dy and ZnGa2O4:Mn. This approach opens a path for less intrusive temperature measurements, particularly in optically opaque multiphase and solid phase combustion environments.

Persistent Emission Properties of SGR J1935+2154 during Its 2020 Active Episode

Abstract We present detailed spectral and temporal characteristics of the persistent X-ray emission of SGR J1935+2154 based on our XMM-Newton and Chandra observations taken in the aftermath of its 2020 April burst storm, during which hundreds of energetic X-ray bursts were emitted, including one associated with an extraordinary fast radio burst. We clearly detect the pulsed X-ray emission in the XMM-Newton data. An average spin-down rate of 1.6 × 10−11 s s−1 is obtained using our spin period measurement combined with three earlier values reported from the same active episode. Our investigations of the XMM-Newton and Chandra spectra with a variety of phenomenological and physically motivated models concluded that the magnetic field topology of SGR J1935+2154 is most likely highly nondipolar. The spectral models indicate that surface field strengths in somewhat localized regions substantially exceed the polar value of 4.4 × 1014 G inferred from a spin-down torque associated with a rotating magnetic dipole.

X-ray emission characteristics in magnetically driven plasma jet experiments on PTS facility

Jets are commonly observed astrophysical phenomena. To study the x-ray emission characteristics of jets, a series of radial foil Z-pinch experiments are carried out on the Primary Test Stand at the Institute of Fluid Physics, China Academy of Engineering Physics. In these experiments, x-ray emission ranging from the soft region (0.1–10 keV) to the hard region (10 keV–500 keV) is observed when the magnetic cavity breaks. The radiation flux of soft x-rays is measured by an x-ray diode and the dose rate of the hard x-rays by an Si-PIN detector. The experimental results indicate that the energy of the soft x-rays is several tens of kilojoules and that of the hard x-rays is ∼200 J. The radiation mechanism of the x-ray emission is briefly analyzed. This analysis indicates that the x-ray energy and the plasma kinetic energy come from the magnetic energy when the magnetic cavity breaks. The soft x-rays are thought to be produced by bremsstrahlung of thermal electrons (∼100 eV), and the hard x-rays by bremsstrahlung of super-hot electrons (∼mega-electron-volt). These results may be helpful to explain the x-ray emission by the jets from young stellar objects.

Characteristics of X-ray Emission from a Micropinch Discharge at Different Polarities of the Discharge Electrodes

The measurement technique and results are presented from studies of the X-ray spectra and X-ray yield from micropinch discharge plasma in a low-inductive vacuum spark device at different polarities of the discharge electrodes. The measurements were performed using the specially designed diagnostic system based on thermoluminescent and scintillation detectors. This made it possible to perform measurements in the photon energy range of 1–300 keV.

Study of temporal and spectral characteristics of the X-ray emission from solar flares

Temporal and spectral characteristics of X-ray emission from 60 flares of intensity ≥C class observed by the Solar X-ray Spectrometer (SOXS) during 2003–2011 are presented. We analyze the X-ray emission observed in four and three energy bands by the Si and Cadmium-Zinc-Telluride (CZT) detectors, respectively. The number of peaks in the intensity profile of the flares varies between 1 and 3. We find moderate correlation (R ≃ 0.2) between the rise time and the peak flux of the first peak of the flare irrespective of energy band, which is indicative of its energy-independent nature. Moreover, the magnetic field complexity of the flaring region is found to be highly anti-correlated (R = 0.61) with the rise time of the flares while positively correlated (R = 0.28) with the peak flux of the flare. The time delay between the peak of the X-ray emission in a given energy band and that in 25–30 keV decreases with increasing energy, suggesting conduction cooling is dominant in the lower energies. Analysis of 340 spectra from 14 flares reveals that the peak of differential emission measure (DEM) evolution is delayed by 60–360 s relative to that of the temperature, and this time delay is inversely proportional to the peak flux of the flare. We conclude that temporal and intensity characteristics of flares are dependent on energy as well as the magnetic field configuration of the active region.

X-pinch X-ray emission on a portable low-current, fast rise-time generator

We report on experiments exploring X-ray emission from an X-pinch driven by a small Marx-waterline generator supplying 50 kA with a risetime of 50 ns and a peak voltage of ∼250 kV. Both standard crossed wire loads and hybrid loads utilizing conical metal electrodes with a single short wire in between them were studied, and in both cases reliable modes of operation were obtained for X-ray radiography. Soft (few keV) and Hard (>5 keV) X-ray emission characteristics were observed. With standard X-pinches, soft radiation emanated from a small hot spot about 3 μm in size, along with hard radiation from a ∼200 μm region close to this hot spot. With hybrid X-pinches, the hot spot was <7 μm in size. There was a clear correlation between the soft and hard X-ray emission—pinches that produced intense soft X-ray emission from a small hot spot also produced the most intense, localized hard X-ray emission.

Characteristics of soft x-ray and extreme ultraviolet (XUV) emission from laser-produced highly charged rhodium ions

We have characterized the soft x-ray and extreme ultraviolet (XUV) emission of rhodium (Rh) plasmas produced using dual pulse irradiation by 150-ps or 6-ns pre-pulses, followed by a 150-ps main pulse. We have studied the emission enhancement dependence on the inter-pulse time separation and found it to be very significant for time separations less than 10 ns between the two laser pulses when using 6-ns pre-pulses. The behavior using a 150-ps pre-pulse was consistent with such plasmas displaying only weak self-absorption effects in the expanding plasma. The results demonstrate the advantage of using dual pulse irradiation to produce the brighter plasmas required for XUV applications.

Energy distribution of relativistic electrons in the kiloparsec scale jet of M 87 with Chandra

The X-ray emission from the jets in active galactic nuclei (AGN) carries important information on the distributions of relativistic electrons and magnetic fields on large scales. We reanalysed archival Chandra observations on the jet of M 87 from 2000 to 2016 with a total exposure of 1460 kiloseconds to explore the X-ray emission characteristics along the jet. We investigated the variability behaviours of the nucleus and the inner jet component HST-1, and confirm indications for day-scale X-ray variability in the nucleus contemporaneous to the 2010 high TeV γ-ray state. HST-1 shows a general decline in X-ray flux over the last few years consistent with its synchrotron interpretation. We extracted the X-ray spectra for the nucleus and all knots in the jet, showing that they are compatible with a single power law within the X-ray band. There are indications that the resultant X-ray photon index exhibit a trend, with slight but significant index variations ranging from ≃ 2.2 (e.g. in knot D) to ≃ 2.4−2.6 (in the outer knots F, A, and B). When viewed in a multiwavelength context, a more complex situation can be seen. Fitting the radio to X-ray spectral energy distributions (SEDs) assuming a synchrotron origin, we show that a broken power-law electron spectrum with break energy Eb around 1 (300 μG/B)1/2 TeV allows a satisfactory description of the multiband SEDs for most of the knots. However, in the case of knots B, C, and D we find indications that an additional high-energy component is needed to adequately reproduce the broad-band SEDs. We discuss the implications and suggest that a stratified jet model may account for the differences.

Measurement of the effective energy of pulsed X-rays emitted from a Mather-type plasma focus device

The current study examined the effective energy of pulsed x-rays emitted from a Mather-type plasma focus device with copper anodes at an energy range of 2–3kJ using x-ray transmission radiography. Aluminum filters of different thicknesses and dental x-ray film were used. When air gas was used at a constant voltage of 21kV at 0.3, 0.6, 0.9 and 1.2 mbar, the effective energy of pulsed the x-ray was 10.9, 10.7, 17.3 and 15.8keV, respectively. At 0.6 mbar of air, as the operating voltage increased to 19, 21 and 23kV, the effective energy of the x-ray radiation was 10.6, 10.7 and 12.4keV, respectively. Comprehensive investigation of the characteristics of x-ray emission from plasma focus devices makes it feasible to use this device as an intensive x-ray generator for medical and industrial purposes. The present study is a part of a program which is planned to realize these applications.

Influence of Xe and Kr impurities on x-ray yield from debris-free plasma x-ray sources with an Ar supersonic gas jet irradiated by femtosecond near-infrared-wavelength laser pulses.

Many aspects of physical phenomena occurring when an intense laser pulse with subpicosecond duration and an intensity of 10^{18}-10^{19}W/cm^{2} heats an underdense plasma in a supersonic clustered gas jet are studied to determine the relative contribution of thermal and nonthermal processes to soft- and hard-x-ray emission from debris-free plasmas. Experiments were performed at the University of Nevada, Reno (UNR) Leopard laser operated with a 15-J, 350-fs pulse and different pulse contrasts (10^{7} or 10^{5}). The supersonic linear (elongated) nozzle generated Xe cluster-monomer gas jets as well as jets with Kr-Ar or Xe-Kr-Ar mixtures with densities of 10^{18}-10^{19}cm^{-3}. Prior to laser heating experiments, all jets were probed with optical interferometry and Rayleigh scattering to measure jet density and cluster distribution parameters. The supersonic linear jet provides the capability to study the anisotropy of x-ray yield from laser plasma and also laser beam self-focusing in plasma, which leads to efficient x-ray generation. Plasma diagnostics included x-ray diodes, pinhole cameras, and spectrometers. Jet signatures of x-ray emission from pure Xe gas, as well as from a mixture with Ar and Kr, was found to be very different. The most intense x-ray emission in the 1-9 KeV spectral region was observed from gas mixtures rather than pure Xe. Also, this x-ray emission was strongly anisotropic with respect to the direction of laser beam polarization. Non-local thermodynamic equilibrium (Non-LTE) models have been implemented to analyze the x-ray spectra to determine the plasma temperature and election density. Evidence of electron beam generation in the supersonic jet plasma was found. The influence of the subpicosecond laser pulse contrast (a ratio between the laser peak intensity and pedestal pulse intensity) on the jets' x-ray emission characteristics is discussed. Surprisingly, it was found that the x-ray yield was not sensitive to the prepulse contrast ratio.

Recent X-ray observations of the symbiotic star AG Peg: do they signify colliding stellar winds?

We present an analysis of recent X-ray observations of the symbiotic star AG Peg. The X-ray emission of AG Peg as observed with Swift in 2015 shows considerable variability on time scale of days as variability on shorter time scales might be present as well. Analysis of the X-ray spectra obtained in 2013 and 2015 confirms that AG Peg is an X-ray source of class $\beta$ of the X-ray sources amongst the symbiotic stars. The X-ray emission of AG Peg as observed with ROSAT (1993 June) might well originate from colliding stellar winds (CSW) in binary system. On the other hand, the characteristics of the X-ray emission of AG Peg in 2013 and 2015 (Swift) are hard to accommodate in the framework of the CSW picture. Analysis of the light curves in 2015 shows that the power spectrum of the X-ray variability in AG Peg resembles that of the flicker noise (or flickering) being typical for accretion processes in astronomical objects. This is a sign that CSWs did not play a key role for the X-ray emission from AG Peg in 2013-2015 and a different mechanism (probably accretion) is also getting into play.

Characteristics of the soft X-ray emission from laser-produced highly charged platinum plasmas

We characterized the spectral structure of the soft X-ray emission and determined the plasma parameters in laser-produced highly charged platinum plasmas. The spectral structure observed originated from Pt21+ to Pt34+ ions, emissions from which overlapped to produce a high output flux in the carbon-window soft X-ray spectral region. Using dual laser pulse irradiation, we observed the maximum output flux, which was 20% larger than that obtained under single-laser irradiation, and the evolution of a strongly absorbed spectral structure, which was attributed to the effects of both opacity and long-scale length of the expanding pre-plasma.

Emergence of hard X-rays at weak nonstationary processes in active regions

Using Suzaku and Reuven Ramaty High Energy Solar Spectroscopic Image (RHESSI) spacecraft data, we study the characteristics of X-ray emission of weak flares at energies when this emission is generated by fluxes of accelerated electrons. Of the 105 events recorded by a broadband monitor of the entire sky (WAM/Suzaku, with an effective area of ~800 cm2 in the energy range from 50 to 300 keV), we consider 64 B1to C3-class flares. The spectra of these events up to 30 keV are built from RHESSI data. We consider some examples of simultaneous recordings of weak flares occurring from 2005 to 2007. The radiation fluxes measured by WAM/Suzaku at 100 keV have been found to be consistent with those expected from the one-parameter approximation of spectra of the nonthermal radiation recorded by RHESSI at lower energies. The average spectral slope for all events under consideration is 4.30 ± 0.15; i.e., these rare events are significantly stricter than the majority of subflares. This can serve as proof of the fact that the particle acceleration in weak flares is more effective than was previously assumed. As in powerful events, these processes occur in the close vicinity of spots or in places where the neutral line separates hills with a large magnetic field strength.

X-RAY EMISSION FROM J1446–4701, J1311–3430, AND OTHER BLACK WIDOW PULSARS

We present the results of detailed X-ray analysis of two black-widow pulsars (BWPs), J1446–4701 and J1311–3430. PSR J1446–4701 is a BWP with orbital parameters near the median values of the sample of known BWPs. Its X-ray emission that was detected by XMM-Newton is well characterized by a soft power-law (PL) spectrum (photon index Γ ≈ 3), and it shows no significant orbital modulations. In view of a lack of radio eclipses and an optical non-detection, the system most likely has a low orbital inclination. PSR J1311–3430 is an extreme BWP with a very compact orbit and the lowest minimum mass companion. Our Chandra data confirm the hard Γ ≈ 1.3 emission seen in previous observations. Through phase-restricted spectral analysis, we found a hint (~2.6σ) of spectral hardening around pulsar inferior conjunction. We also provide a uniform analysis of the 12 BWPs observed with Chandra and compare their X-ray properties. Pulsars with soft, Γ > 2.5 emission seem to have lower than average X-ray and γ-ray luminosities. We do not, however, see any other prominent correlation between the pulsar's X-ray emission characteristics and any of its other properties. The contribution of the intra-binary shock to the total X-ray emission, if any, is not discernible in this sample of pulsars with shallow observations.

AN EXTRAORDINARY OUTBURST OF THE MAGNETAR SWIFT J1822.3–1606

The 2011 outburst of Swift J1822.3–1606 was extraordinary; periodic modulations at the spin period of the underlying neutron star were clearly visible, remarkably similar to what is observed during the decaying tail of magnetar giant flares. We investigated the temporal characteristics of X-ray emission during the early phases of the outburst. We performed a periodicity search with the spectral hardness ratio (HR) and found a coherent signal near the spin period of the neutron star, but with a lag of about 3 radians. Therefore, the HR is strongly anti-correlated with the X-ray intensity, which is also seen in the giant flares. We studied the time evolution of the pulse profile and found that it evolves from a complex morphology to a much simpler shape within about a month. Pulse profile simplification also takes place during the giant flares, but on a much shorter timescale of about a few minutes. We found that the amount of energy emitted during the first 25 days of the outburst is comparable to what was detected in minutes during the decaying tail of giant flares. Based on these similarities, we suggest that the triggering mechanisms of the giant flares and the magnetar outbursts are likely the same. We propose that the trapped fireball that develops in the magnetosphere at the onset of the outburst radiates away efficiently in minutes in magnetars exhibiting giant flares, while in other magnetars, such as Swift J1822.3–1606, the efficiency of radiation of the fireball is not as high and, therefore, lasts much longer.

Characteristics of x-ray emission from optically thin high-Z plasmas in the soft x-ray region

The characteristics of soft x-ray emission from optically thin high-Z plasmas of gold, lead and bismuth were investigated with the large helical device. Compared to optically thicker laser-produced plasmas, significantly different spectral structures were observed due to the difference in opacities and electron temperatures. Peak structures appearing in unresolved transition arrays were identified by calculations using atomic structure codes. The main contributors of discrete line emission in each case were Pd-, Ag-, and Rh-like ion stages. The present calculations point to the overestimation of contributions for 4p–4d transitions based on intensity estimates arising purely from gA distributions that predict strong emission from 4p–4d transitions. Understanding of such spectral emission is not only important for the completion of databases of high-Z highly ion charge states but also the development of promising high brightness sources for biological imaging applications.

Generation of hard X-ray emission by the electron beam in plasma focus facilities

The results of measurements of the temporal characteristics of hard X-ray emission generated at plasma focus (PF) facilities are presented. Mechanisms of electron beam generation in the PF pinch are analyzed. On the basis of the known mechanisms and experimental data on the measured temporal characteristics of hard X-ray pulses, a mechanism of fast electron generation that takes into account both the effect of the anomalous pinch resistance and the current redistribution in the near-pinch region is proposed. The processes occurring in the pinch plasma are simulated on the basis of the proposed mechanism by using the MicroCap code. It is shown that only a small fraction of the discharge current (1–10%) can be transformed into the electron beam current.

Optimization of neon soft X-rays emission from 200 J fast miniature dense plasma focus device: A potential source for soft X-ray lithography

Abstract The neon soft X-ray (SXR) emission characteristics of a Fast Miniature Plasma Focus (FMPF-3) device have been investigated. The FMPF-3 device used for our experiment is of sub-kilojoule energy capacity, which is an order of magnitude lesser than the other well established plasma focus devices. The influence of different geometrical parameters of the anode and the pressure of the filling gas on the SXR emission was investigated to optimize the neon SXR yield and thereby make it a potential source for X-ray lithography. The SXR signal, solely from the desired, characteristic spectral range (900–1600) eV was selectively extracted and acquired using appropriate X-ray absorption filters on diode X-ray spectrometer. It was found that the neon SXR emission from 17 mm long cylindrical anode, which produced best neutron yields, was rather poor, in a very narrow pressure range and that too at low operating pressure. With decrease in the length of cylindrical anode, the optimum operating pressure shifts to higher pressure side, the working pressure range widens and the SXR yield also increases until the anode length is reduced to 12 mm, after which, the SXR yield and working pressure range start to degrade. The highest neon SXR yield of 1.1 J/shot, corresponding to a wall plug efficiency of 0.57%, was obtained for 12 mm long cylindrical anode. The tapered anodes with different length were also designed and tested, but they did not show any significant improvement in neon SXR yield.

Theoretical study on angular distribution and polarization characteristics of X-ray emission following dielectronic recombination of lithium-like ions

Based on the multiconfiguration Dirac-Fock method and the theory of density matrix, we have calculated the magnetic sublevel captured cross section of intermediate doubly-excited state 1s2s22p3/2J = 1 formed by dielectronic recombination of lithium-like ions (26 Z 92). Then, we obtain the angular distribution and linear polarization of X-rays of electric-dipole radiation 1s2s22p3/2J = 11s22s2J = 0. In this study, emphasis is placed on the effects of the Breit interaction on the relevant physical quantities. We find that the influences of the Breit interaction on the alignment for the capture to the doubly-excited state 1s2s22p3/2J = 1 are dramatic, resulting in the remarkable change in the angular distribution and polarization properties of the X-ray emission.

A Survey of the Hard X-Ray Characteristics of Seismically Active and Quiet White-Light Flares

Various mechanisms have been proposed to explain how seismic waves can be generated during a solar flare, several of which include a major role for accelerated electrons. To address this question further, we have selected two samples of white-light flares (WLFs): one that has associated sunquakes, and one that does not. We focus particularly on the spatial characteristics of the hard X-ray (HXR) and WL emission, and the HXR spectral characteristics associated with the flares in both samples, including spectral hardness, HXR source size, and total injected electron power. Coupling the determined rate of energy deposition with the area over which the energy is being deposited suggests that in general the acoustically active flares are associated with a larger and more impulsive deposition of electron energy. However, this does not always correspond to a higher WL contrast.