scholarly journals Spectrum formation in X-ray pulsars at very low mass accretion rate: Monte Carlo approach

2021 ◽  
Vol 503 (4) ◽  
pp. 5193-5203
Author(s):  
Alexander A Mushtukov ◽  
Valery F Suleimanov ◽  
Sergey S Tsygankov ◽  
Simon Portegies Zwart
Keyword(s):  
Monte Carlo ◽  
Neutron Star ◽  
Spectral Characteristics ◽  
Electron Gas ◽  
High Energy ◽  
Spectral Shape ◽  
Absorption Feature ◽  
X Rays ◽  
Component Structure ◽  
X Ray

ABSTRACT Recently, it has been discovered that the transition of X-ray pulsars to the low luminosity state ($L\lesssim 10^{35}\, {\rm erg\ \rm s^{-1}}$) is accompanied by a dramatic spectral change. That is, the typical power-law-like spectrum with high-energy cut-off transforms into a two-component structure with a possible cyclotron absorption feature on top of it. It was proposed that these spectral characteristics can be explained qualitatively by the emission of cyclotron photons in the atmosphere of the neutron star caused by collisional excitation of electrons to upper Landau levels and further Comptonization of the photons by electron gas. The electron gas are expected to be overheated in a thin top layer of the atmosphere. In this paper, we perform Monte Carlo simulations of the radiative transfer in the atmosphere of an accreting neutron star while accounting for a resonant scattering of polarized X-ray photons by thermally distributed electrons. The spectral shape is shown to be strongly polarization-dependent in soft X-rays ($\lesssim 10\, {\rm keV}$) and near the cyclotron scattering feature. The results of our numerical simulations are tested against the observational data of the X-ray pulsar A 0535+262 in the low-luminosity state. We show that the spectral shape of the pulsar can be reproduced by the proposed theoretical model. We discuss applications of the discovery to the observational studies of accreting neutron stars.

scholarly journals Characterization of laser-driven electron and photon beams using the Monte Carlo code FLUKA

2014 ◽  
Vol 32 (2) ◽  
pp. 233-241 ◽  
Author(s):  
F. Fiorini ◽  
D. Neely ◽  
R.J. Clarke ◽  
S. Green
Keyword(s):  
Monte Carlo ◽  
Electron Temperature ◽  
Spectral Characteristics ◽  
Simulation Method ◽  
Target Thickness ◽  
Monte Carlo Code ◽  
X Rays ◽  
Photon Beams ◽  
X Ray ◽  
Plasma Effects

AbstractWe present a new simulation method to predict the maximum possible yield of X-rays produced by electron beams accelerated by petawatt lasers irradiating thick solid targets. The novelty of the method lies in the simulation of the electron refiluxing inside the target implemented with the Monte Carlo code Fluka. The mechanism uses initial theoretical electron spectra, cold targets and refiluxing electrons forced to re-enter the target iteratively. Collective beam plasma effects are not implemented in the simulation. Considering the maximum X-ray yield obtained for a given target thickness and material, the relationship between the irradiated target mass thickness and the initial electron temperature is determined, as well as the effect of the refiluxing on X-ray yield. The presented study helps to understand which electron temperature should be produced in order to generate a particular X-ray beam. Several applications, including medical and security imaging, could benefit from laser generated X-ray beams, so an understanding of the material and the thickness maximizing the yields or producing particular spectral characteristics is necessary. On the other more immediate hand, if this study is experimentally reproduced at the beginning of an experiment in which there is an interest in laser-driven electron and/or photon beams, it can be used to check that the electron temperature is as expected according to the laser parameters.

scholarly journals Thermal Or Non–Thermal X–Rays From AGNs?

1994 ◽  
Vol 159 ◽  
pp. 33-36
Author(s):  
Gabriele Ghisellini ◽  
Francesco Haardt
Keyword(s):  
High Energy ◽  
Spectral Shape ◽  
X Rays ◽  
Two Phase ◽  
X Ray ◽  
Galactic Black Hole ◽  
Phase Models ◽  
Hot Corona ◽  
High Energy Emission ◽  
Cold Matter

Recent data from OSSE on CGRO and SIGMA on GRANAT challenge the non-thermal interpretation of the origin of the high energy emission of AGNs, showing that the hard X-ray spectra of several Seyfert AGN are steep like those of Galactic black hole candidates. Thermal models are therefore favoured. Two–phase models, in which a hot corona is placed above a relatively cold accretion disk can account for the observed X–ray spectra and the correlated variability in the UV and X–ray bands. Cold matter, both in the vicinity of the nucleous, and located further away in the torus surrounding the nucleous, may modify substantially the spectrum with important consequences on the expected variability and spectral shape.

scholarly journals Discovery of X-ray pulsations in the Be/X-ray binary IGR J06074+2205

2018 ◽  
Vol 613 ◽  
pp. A52 ◽  
Author(s):  
P. Reig ◽  
A. Zezas
Keyword(s):  
Neutron Star ◽  
Model Fitting ◽  
High Energy ◽  
X Rays ◽  
Energy Bands ◽  
X Ray ◽  
Be Star ◽  
Best Fitting ◽  
Open Question ◽  
Star Surface

Context. IGR J06074+2205 is a poorly studied X-ray source with a Be star companion. It has been proposed to belong to the group of Be/X-ray binaries (BeXBs). In BeXBs, accretion onto the neutron star occurs via the transfer of material from the Be star’s circumstellar disk. Thus, in the absence of the disk, no X-ray should be detected. Aims. The main goal of this work is to study the quiescent X-ray emission of IGR J06074+2205 during a disk-loss episode. Methods. We obtained light curves at different energy bands and a spectrum covering the energy range 0.4–12 keV. We used Fourier analysis to study the aperiodic variability and epoch folding methods to study the periodic variability. Model fitting to the energy spectrum allowed us to identify the possible physical processes that generated the X-rays. Results. We show that at the time of the XMM-Newton observation, the decretion disk around the Be star had vanished. Still, accretion appears as the source of energy that powers the high-energy radiation in IGR J06074+2205. We report the discovery of X-ray pulsations with a pulse period of 373.2 s and a pulse fraction of ~50%. The 0.4–12 keV spectrum is well described by an absorbed power law and blackbody components with the best fitting parameters: NH = (6.2 ± 0.5) × 1021 cm−2, kTbb = 1.16 ± 0.03 keV, and Γ = 1.5 ± 0.1. The absorbed X-ray luminosity is LX = 1.4 × 1034 erg s−1 assuming a distance of 4.5 kpc. Conclusions. The detection of X-ray pulsations confirms the nature of IGR J06074+2205 as a BeXB. We discuss various scenarios to explain the quiescent X-ray emission of this pulsar. We rule out cooling of the neutron star surface and magnetospheric emission and conclude that accretion is the most likely scenario. The origin of the accreted material remains an open question.

scholarly journals Investigation of the Timing and Spectral Properties of an Ultraluminous X-Ray Pulsar NGC 7793 P13

2022 ◽  
Vol 924 (2) ◽  
pp. 65
Author(s):  
Lupin Chun-Che Lin ◽  
Chin-Ping Hu ◽  
Jumpei Takata ◽  
Kwan-Lok Li ◽  
C. Y. Hui ◽  
...  
Keyword(s):  
Resonant Scattering ◽  
Periodic Variation ◽  
Gaussian Mixture ◽  
High Energy ◽  
Absorption Feature ◽  
X Rays ◽  
Pulse Profile ◽  
X Ray ◽  
Test Taking ◽  
Orbital Phase

Abstract We perform both timing and spectral analyses using the archival X-ray data taken with Swift, XMM-Newton, NICER, and NuSTAR from 2016 to 2020 to study an ultraluminous pulsar, NGC 7793 P13, that showed a long period of super-Eddington accretion. We use the Rayleigh test to investigate the pulsation at different epochs, and confirm the variation of the pulse profile with finite Gaussian mixture modeling and a two-sample Kuiper test. Taking into account the periodic variation of the spin periods caused by the orbital Doppler effect, we further determine an orbital period of ∼65 days and show that no significant correlation can be detected between the orbital phase and the pulsed fraction. The pulsed spectrum of NGC 7793 P13 in the 0.5–20 keV range can be simply described using a power law with a high-energy exponential cutoff, while the broadband phase-averaged spectrum of the same energy range requires two additional components to account for the contribution of a thermal accretion disk and the Comptonization photons scattered into the hard X-rays. We find that NGC 7793 P13 stayed in the hard ultraluminous state and the pulsed spectrum was relatively soft when the source was faint at the end of 2019. Moreover, an absorption feature close to 1.3 keV is marginally detected from the pulsed spectra and it is possibly associated with a cyclotron resonant scattering feature.

scholarly journals Constraints of the compactness of the isolated neutron stars via X-ray phase-resolved spectroscopy

2012 ◽  
Vol 8 (S291) ◽  
pp. 393-395
Author(s):  
V. Hambaryan ◽  
V. Suleimanov ◽  
R. Neuhäuser ◽  
K. Werner
Keyword(s):  
Magnetic Field ◽  
Neutron Star ◽  
Physical Properties ◽  
Neutron Stars ◽  
Field Component ◽  
Spectral Shape ◽  
Absorption Feature ◽  
Broad Absorption ◽  
X Ray ◽  
Distribution Parameters

AbstractA model with a condensed iron surface and partially ionized hydrogen-thin atmosphere allows us to fit simultaneously the observed general spectral shape and the broad absorption feature (observed at 0.3 keV) in different spin phases of the isolated neutron star RBS 1223. We constrain some physical properties of the X-ray emitting areas, i.e. the temperatures (Tpole1 ~ 105 eV, Tpole2 ~ 99 eV), magnetic field strengths (Bpole1 ≈ Bpole2 ~ 8.6 × 1013 G) at the poles, and their distribution parameters (a1 ~ 0.61, a2 ~ 0.29, indicating an absence of strong toroidal magnetic field component). In addition, we are able to place some constraints on the geometry of the emerging X-ray emission and the gravitational redshift (z ~ 0.160.03−0.01) of the isolated neutron star RBS 1223.

The Basic Physical Principles of Ion, Electron, and X-Ray Detectors and Their Application to Microanalysis

1985 ◽  
Vol 43 ◽  
pp. 154-157
Author(s):  
A.J. Tousimis
Keyword(s):  
Ion Beam ◽  
Depth Resolution ◽  
Sample Surface ◽  
High Energy ◽  
X Rays ◽  
X Ray ◽  
Electrons And Ions ◽  
Spatial Depth ◽  
Minimum Surface Area ◽  
Physical Principles

An integral and of prime importance of any microtopography and microanalysis instrument system is its electron, x-ray and ion detector(s). The resolution and sensitivity of the electron microscope (TEM, SEM, STEM) and microanalyzers (SIMS and electron probe x-ray microanalyzers) are closely related to those of the sensing and recording devices incorporated with them.Table I lists characteristic sensitivities, minimum surface area and depth analyzed by various methods. Smaller ion, electron and x-ray beam diameters than those listed, are possible with currently available electromagnetic or electrostatic columns. Therefore, improvements in sensitivity and spatial/depth resolution of microanalysis will follow that of the detectors. In most of these methods, the sample surface is subjected to a stationary, line or raster scanning photon, electron or ion beam. The resultant radiation: photons (low energy) or high energy (x-rays), electrons and ions are detected and analyzed.

scholarly journals Monte Carlo Modeling and Design of Photon Energy Attenuation Layers for >10× Quantum Yield Enhancement in Si-Based Hard X-ray Detectors

Instruments ◽  
2021 ◽  
Vol 5 (2) ◽  
pp. 17
Author(s):  
Eldred Lee ◽  
Kaitlin M. Anagnost ◽  
Zhehui Wang ◽  
Michael R. James ◽  
Eric R. Fossum ◽  
...  
Keyword(s):  
Monte Carlo Simulation ◽  
Monte Carlo ◽  
Quantum Yield ◽  
Photon Energy ◽  
High Efficiency ◽  
High Energy ◽  
Yield Enhancement ◽  
X Ray ◽  
Simulation Results ◽  
Conversion Efficiencies

High-energy (>20 keV) X-ray photon detection at high quantum yield, high spatial resolution, and short response time has long been an important area of study in physics. Scintillation is a prevalent method but limited in various ways. Directly detecting high-energy X-ray photons has been a challenge to this day, mainly due to low photon-to-photoelectron conversion efficiencies. Commercially available state-of-the-art Si direct detection products such as the Si charge-coupled device (CCD) are inefficient for >10 keV photons. Here, we present Monte Carlo simulation results and analyses to introduce a highly effective yet simple high-energy X-ray detection concept with significantly enhanced photon-to-electron conversion efficiencies composed of two layers: a top high-Z photon energy attenuation layer (PAL) and a bottom Si detector. We use the principle of photon energy down conversion, where high-energy X-ray photon energies are attenuated down to ≤10 keV via inelastic scattering suitable for efficient photoelectric absorption by Si. Our Monte Carlo simulation results demonstrate that a 10–30× increase in quantum yield can be achieved using PbTe PAL on Si, potentially advancing high-resolution, high-efficiency X-ray detection using PAL-enhanced Si CMOS image sensors.

A multi-length-scale USAXS/SAXS facility: 10–50 keV small-angle X-ray scattering instrument

2013 ◽  
Vol 46 (5) ◽  
pp. 1508-1512 ◽  
Author(s):  
Byron Freelon ◽  
Kamlesh Suthar ◽  
Jan Ilavsky
Keyword(s):  
Small Angle ◽  
Soft Matter ◽  
High Energy ◽  
X Rays ◽  
X Ray ◽  
X Ray Scattering ◽  
Wide Range ◽  
And Performance ◽  
New Facility ◽  
Ray Scattering

Coupling small-angle X-ray scattering (SAXS) and ultra-small-angle X-ray scattering (USAXS) provides a powerful system of techniques for determining the structural organization of nanostructured materials that exhibit a wide range of characteristic length scales. A new facility that combines high-energy (HE) SAXS and USAXS has been developed at the Advanced Photon Source (APS). The application of X-rays across a range of energies, from 10 to 50 keV, offers opportunities to probe structural behavior at the nano- and microscale. An X-ray setup that can characterize both soft matter or hard matter and high-Zsamples in the solid or solution forms is described. Recent upgrades to the Sector 15ID beamline allow an extension of the X-ray energy range and improved beam intensity. The function and performance of the dedicated USAXS/HE-SAXS ChemMatCARS-APS facility is described.

A high-energy triple-axis X-ray diffractometer for the study of the structure of bulk crystals

2004 ◽  
Vol 37 (6) ◽  
pp. 901-910 ◽  
Author(s):  
C. Seitz ◽  
M. Weisser ◽  
M. Gomm ◽  
R. Hock ◽  
A. Magerl
Keyword(s):  
High Energy ◽  
X Rays ◽  
Bulk Crystals ◽  
X Ray Diffraction ◽  
X Ray ◽  
Peak Intensity ◽  
High Penetration ◽  
Massive Sample ◽  
Laue Geometry ◽  
The Ideal

A triple-axis diffractometer for high-energy X-ray diffraction is described. A 450 kV/4.5 kW stationary tungsten X-ray tube serves as the X-ray source. Normally, 220 reflections of thermally annealed Czochralski Si are employed for the monochromator and analyser. Their integrated reflectivity is about ten times higher than the ideal crystal value. With the same material as the sample, and working with the WKα line at 60 keV in symmetric Laue geometry for all axes, the full width at half-maximum (FWHM) values for the longitudinal and transversal resolution are 2.5 × 10−3and 1.1 × 10−4for ΔQ/Q, respectively, and the peak intensity for a non-dispersive setting is 3000 counts s−1. In particular, for a double-axis mode, an energy well above 100 keV from theBremsstrahlungspectrum can be used readily. High-energy X-rays are distinguished by a high penetration power and materials of several centimetre thickness can be analysed. The feasibility of performing experiments with massive sample environments is demonstrated.

scholarly journals A hydroxyapatite phantom material for the calibration of in vivo x-ray fluorescence systems of bone strontium and lead quantification

2021 ◽  
Author(s):  
Eric Da Silva
Keyword(s):  
Monte Carlo ◽  
Soft Tissue ◽  
Monte Carlo Simulations ◽  
Calibration Procedure ◽  
X Rays ◽  
X Ray ◽  
Total Phosphate Concentration ◽  
High Concentrations ◽  
Phantom Material

A hydroxyaptite [HAp; Ca5(PO4)3OH] phantom material was developed with the goal of improving the calibration protocol of the 125I-induced in vivo X-ray fluorescence (IVXRF) system of bone strontium quantification with further application to other IVXRF bone metal quantification systems, particulary those associated with bone lead quantification. It was found that calcium can be prepared pure of inherent contamination from strontium (and other elements) through a hydroxide precipitation producing pure Ca(OH)2, thereby, allowing for the production of a blank phantom which has not been available previously. The pure Ca(OH)2 can then be used for the preparation of pure CaHPO4 ⋅ 2H2O. A solid state pure HAp phantom can then be prepared by reaction of Ca(OH)2 and CaHPO4 ⋅ 2H2O mixed as to produce a Ca/P mole ratio of 1.67, that in HAp and the mineral phase of bone, in the presence of a setting solution prepared as to raise the total phosphate concentration of the solution by increasing the solubility CaHPO4 ⋅ 2H2O and thereby precipitating HAp. The procedure can only be used to prepare phantoms in which doping with the analyte does not disturb the Ca/P ratio substantially. In cases in which phantoms are to be prepared with high concentrations of strontium, the cement mixture can be modified as to introduce strontium in the form of Sr(OH)2 ⋅ 8H2O as to maintain a (Ca + Sr)/P ratio of 1.67. It was found by both X-ray diffraction spectrometry and Raman spectroscopy studies that strontium substitutes for calcium as in bone when preparing phantoms by this route. The necessity for the blank bone phantoms was assessed through the first blank bone phantom measurement and Monte Carlo simulations. It was found that for the 125I-induced IVXRF system of bone strontium quantification, the source, 125I brachytherapy seeds may be contributing coherently and incoherently scattered zirconium X-rays to the measured spectra, thereby requiring the use of the blank bone phantom as a means of improving the overall quantification methodology. Monte Carlo simulations were employed to evaluate any improvement by the introduction of HAp phantoms into the coherent normalization-based calibration procedure. It was found that HAp phantoms remove the need for a coherent conversion factor (CCF) thereby potentially increasing accuracy of the quantification. Further, it was found that in order for soft tissue attenuation corrections to be possible using spectroscopic information alone, HAp along with a suitable soft tissue surrogate material need to be employed. The HAp phantom material was used for the evaluations of portable X-ray analyzer systems for their potential for IVXRF quantification of lead and strontium with a focus on a comparison between tungsten, silver and rhodium target systems. Silver and rhodium target X-ray tube systems were found to be comparable for this quantification.

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