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1
Godleski, John J., Rebecca C. Stearns i Emil J. Millet. "Electron spectroscopic imaging and analysis of electron energy loss spectra with an energy filtering Electron Microscope". Proceedings, annual meeting, Electron Microscopy Society of America 47 (6.08.1989): 404–5. http://dx.doi.org/10.1017/s0424820100153993.
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The Zeiss CEM902, energy filtering electron microscope, can be used to image the structure of unstained 30 nm sections of biologic materials, to image the distribution of selected elements in such sections, and to determine electron energy loss spectra (EELS) of elements in areas as small as 10 nm. Although the integrated computer in the latest version of the CEM902 can collect and display signals from the scintillation detector for recording EELS, our instrument did not have this capability. Therefore, we have added a Leading Edge Model D personal computer with a 20 Mbyte hard disk, Hercules compatible graphics display adapter, and a programmable gain analog to digital converter board (Metrabyte DAS16-G1) to collect and analyze voltage signals corresponding to changes in accelerating voltage and changes in the signal from the photomultiplier tube (PMT) of the scintillation detector. With this board, the gain on the PMT channel is dynamically adjusted for optimal resolution. Software is designed to monitor and display voltages, store data on the hard disk, display spectra with adjustable axes, as well as subtract spectra and determine areas beneath regions of interest.Canine alveolar macrophages with ingested cobalt oxide particles were fixed with 2.5% glutaraldehyde in 0.164M phosphate buffer, post-fixed in 1% OsO4 in 0.lM Na cacodylate buffer, dehydrated through alcohols, embedded in araldite, and sectioned at 30nm. Sections were assessed with our CEM902 as described above. The spectral range of 500 to 900 electron volts while focused on acobalt oxide particle at 20,000x is illustrated in Figure 1 .
2
Wadiasingh, Zorawar, Matthew G. Baring, Peter L. Gonthier i Alice K. Harding. "Hard Spectral Tails in Magnetars". Proceedings of the International Astronomical Union 13, S337 (wrzesień 2017): 108–11. http://dx.doi.org/10.1017/s1743921317009073.
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AbstractPulsed non-thermal quiescent emission between 10 keV and around 150 keV has been observed in ~10 magnetars. For inner magnetospheric models of such hard X-ray signals, resonant Compton upscattering of soft thermal photons from the neutron star surface is the most efficient radiative process. We present angle-dependent hard X-ray upscattering model spectra for uncooled monoenergetic relativistic electrons. The spectral cut-off energies are critically dependent on the observer viewing angles and electron Lorentz factor. We find that electrons with energies less than around 15 MeV will emit most of their radiation below 250 keV, consistent with the observed turnovers in magnetar hard X-ray tails. Moreover, electrons of higher energy still emit most of the radiation below around 1 MeV, except for quasi-equatorial emission locales for select pulses phases. Our spectral computations use new state-of-the-art, spin-dependent formalism for the QED Compton scattering cross section in strong magnetic fields.
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Khangulyan, Dmitry, Andrew M. Taylor i Felix Aharonian. "The Formation of Hard Very High Energy Spectra from Gamma-ray Burst Afterglows via Two-zone Synchrotron Self-Compton Emission". Astrophysical Journal 947, nr 2 (1.04.2023): 87. http://dx.doi.org/10.3847/1538-4357/acc24e.
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Abstract Electron Compton scattering of target photons into the gamma-ray energy band (inverse Compton scattering; IC) is commonly expected to dominate the very high energy (VHE) spectra in gamma-ray bursts (GRBs) especially during the afterglow phase. For sufficiently large center-of-mass energies in these collisions, the effect of the electron recoil starts reducing the scattering cross-section (the Klein–Nishina regime). The IC spectra generated in the Klein–Nishina regime is softer and has a smaller flux level compared to the synchrotron spectra produced by the same electrons. The detection of afterglow emission from nearby GRB190829A in the VHE domain with H.E.S.S. has revealed an unexpected feature: the slope of the VHE spectrum matches well the slope of the X-ray spectra, despite expectations that, for the IC production process, the impact of the Klein–Nishina effect should be strong. The multi-wavelength spectral energy distribution appears to be inconsistent with predictions of one-zone synchrotron–self-Compton models. We study the possible impact of two-zone configuration on the properties of IC emission when the magnetic field strength differs considerably between the two zones. Synchrotron photons from the strong magnetic field zone provide the dominant target for cooling of the electrons in the weak magnetic field zone, which results in a formation of hard electron distribution and consequently of a hard IC emission. We show that the two-zone model can provide a good description of the Swift's X-ray Telescope and VHE H.E.S.S. data.
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Breuhaus, Mischa, Joachim Hahn, Carlo Romoli, Brian Reville, Gwenael Giacinti, James Anthony Hinton i Richard Tuffs. "Ultra-high energy inverse Compton emission from Galactic electron accelerators". EPJ Web of Conferences 280 (2023): 02001. http://dx.doi.org/10.1051/epjconf/202328002001.
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It is generally held that >100 TeV emission from astrophysical objects unambiguously demonstrates the presence of PeV protons or nuclei, due to the unavoidable Klein–Nishina suppression of inverse Compton emission from electrons. However, in the presence of inverse Compton dominated cooling, hard high-energy electron spectra are possible. We show that the environmental requirements for such spectra can naturally be met in spiral arms, and in particular in regions of enhanced star formation activity, the natural locations for the most promising electron accelerators: powerful young pulsars. Leptonic scenarios are applied to gamma-ray sources recently detected by the High-Altitude Water Cherenkov Observatory (HAWC) and the Large High Altitude Air Shower Observatory (LHAASO). We show that these sources can indeed be explained by inverse Compton emission.
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Rudawy, P., M. Siarkowski i R. Falewicz. "Plasma heating in the initial phase of solar flares". Proceedings of the International Astronomical Union 5, S264 (sierpień 2009): 282–84. http://dx.doi.org/10.1017/s1743921309992791.
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AbstractIn this paper we analyze soft and hard X-ray emission of the 2002 September 20 M1.8 GOES class solar flare observed by RHESSI and GOES satellites, where soft X-ray emission precedes the onset of the main bulk hard X-ray emission by ~5 min. This suggests that an additional heating mechanism may be at work at the early beginning of the flare. However RHESSI spectra indicate presence of the non-thermal electrons also before impulsive phase. So, we assumed that a dominant energy transport mechanism during rise phase of solar flares is electron beam-driven evaporation. We used non-thermal electron beams derived from RHESSI spectra as the heating source in a hydrodynamic model of the analyzed flare. We showed that energy delivered by non-thermal electron beams is sufficient to heat the flare loop to temperatures in which it emits soft X-ray closely following the GOES 1–8 Å light-curve.
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Kundu, M. R., S. M. White, N. Gopalswamy i J. Lim. "Millimeter, Microwave, Hard X-Ray, and Soft X-Ray Observations of Energetic Electron Populations in Solar Flares". International Astronomical Union Colloquium 142 (1994): 599–610. http://dx.doi.org/10.1017/s0252921100077873.
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AbstractWe present comparisons of multiwavelength data for a number of solar flares observed during the major campaign of 1991 June. The different wavelengths are diagnostics of energetic electrons in different energy ranges: soft X-rays are produced by electrons with energies typically below 10 keV, hard X-rays by electrons with energies in the range 10-200 keV, microwaves by electrons in the range 100 keV-1 MeV, and millimeter-wavelength emission by electrons with energies of 0.5 MeV and above. The flares in the 1991 June active period were remarkable in two ways: all have very high turnover frequencies in their microwave spectra, and very soft hard X-ray spectra. The sensitivity of the microwave and millimeter data permit us to study the more energetic (>0.3 MeV) electrons even in small flares, where their high-energy bremsstrahlung is too weak for present detectors. The millimeter data show delays in the onset of emission with respect to the emissions associated with lower energy electrons and differences in time profiles, energy spectral indices incompatible with those implied by the hard X-ray data, and a range of variability of the peak flux in the impulsive phase when compared with the peak hard X-ray flux which is two orders of magnitude larger than the corresponding variability in the peak microwave flux. All these results suggest that the hard X-ray-emitting electrons and those at higher energies which produce millimeter emission must be regarded as separate populations. This has implications for the well-known “number problem” found previously when comparing the numbers of nonthermal electrons required to produce the hard X-ray and radio emissions.Subject headings: Sun: flares — Sun: radio radiation — Sun: X-rays, gamma rays
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Bespalov, P. A., V. V. Zaitsev i A. V. Stepanov. "Energetic Particles in a Flare Loop: Spectra and Radiation Signatures". Symposium - International Astronomical Union 142 (1990): 421–27. http://dx.doi.org/10.1017/s0074180900088343.
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It has been shown that high energy particle spectra, particle dynamics, and radiation in a flare loop are determined by wave-particle interactions. The electron-whistler interaction occurs under conditions of strong pitch angle diffusion that makes the particle distribution function isotropic. The flare loop electrons retain information about the particle source spectrum. The interaction of energetic ions with Alfven waves is characterized by strong, moderate, and weak diffusion. The time delays in hard X-ray and gamma-ray emission during one-step acceleration processes might be understood in terms of a trap-plus-turbulent propagation model. The density of precipitating particles is less than or equal to the trapping one. Radiation signatures of flare loop electrons are discussed.
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Hu, Wen, Da-Hai Yan i Qiang-Lin Hu. "Two-injection Scenario for the Hard X-Ray Excess Observed in Mrk 421". Astrophysical Journal 948, nr 2 (1.05.2023): 82. http://dx.doi.org/10.3847/1538-4357/accc2e.
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Abstract An interesting result that was recently reported for Mrk 421 is the detection of a significant excess at hard X-ray energies, which could provide useful information to investigate particle acceleration and emission mechanisms in the relativistic jet. Considering a two-injection scenario, we develop a self-consistent one-zone leptonic model to understand the origin of the hard X-ray excess in Mrk 421 during the period of extremely low X-ray and very high-energy flux in 2013 January. In the model, two populations of mono-energetic ultra-relativistic electrons are injected into the emission region, which is a magnetized plasmoid propagating along the blazar jet. We numerically calculate the emitting electron energy distribution by solving a kinetic equation that incorporates both shock acceleration and stochastic acceleration processes. Moreover, we infer analytic expressions relating the electrons’ acceleration, cooling, escape, and injection to the observed spectra and variability. In particular, for the injection luminosity, we derive a new approximate analytical expression for the case of continual injection with a mono-energetic distribution. Based on a comparison between the theoretical predictions and the observed SED, we conclude that the hard X-ray excess that was observed in Mrk 421 may be due to the synchrotron radiation emitted by an additional electron population, which is co-spatial with an electron population producing simultaneous optical/UV, soft X-ray, and γ-ray emissions. Therefore, stochastic acceleration may play a major role in producing the observed X-ray spectrum.
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Zhang, S. N. "High Energy Continuum Spectra from X-Ray Binaries". International Astronomical Union Colloquium 163 (1997): 41–52. http://dx.doi.org/10.1017/s0252921100042482.
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AbstractA variety of high energy (>1 keV) spectra have been observed in recent years from Black Hole (BH) and Neutron Star (NS) X-ray Binaries (XB). Some common physical components exist between BHXBs and NSXBs, resulting in some high energy spectral features. A common component between a BHXB and a weakly magnetized NSXB is the inner accretion disk region extending very close to the surface (for a NS) or the horizon (for a BH). The inner disk radiation can be described by a multi-color blackbody (MCB) spectral model. The surface radiation of the NS can be approximated by a Single Color Blackbody (SCB) spectrum. For a strongly magnetized NSXB, the high energy emission is from its magnetosphere, characterised by a thermal bremsstrahlung (TB) spectrum. In both BHXBs and weakly magnetized NSXBs, a hot electron cloud may exist, producing the hard X-ray power law (photon index −1.5 to −2.0) with thermal cutoff (50–200 keV). It has been recently proposed that a converging flow may be formed near the horizon of a BH, producing a softer power law (photon index about −2.5) without cutoff up to several hundred keV. Based on these concepts we also discuss possible ways to distinguish between BH and NS XBs. Finally we discuss briefly spectral state transitions in both BH and NS XBs.
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Ham, Seunggi, Jonghyeon Ryu, Hakmin Lee, Sungbin Park, Y. C. Ghim, Y. S. Hwang i Kyoung-Jae Chung. "Estimation of plasma parameters of X-pinch with time-resolved x-ray spectroscopy". Matter and Radiation at Extremes 8, nr 3 (1.05.2023): 036901. http://dx.doi.org/10.1063/5.0131369.
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We estimate the parameters of a Cu plasma generated by an X-pinch by comparing experimentally measured x-rays with synthetic data. A filtered absolute extreme ultraviolet diode array is used to measure time-resolved x-ray spectra with a spectral resolution of ∼1 keV in the energy range of 1–10 keV. The synthetic spectra of Cu plasmas with different electron temperatures, electron densities, and fast electron fractions are calculated using the FLYCHK code. For quantitative comparison with the measured spectrum, two x-ray power ratios with three different spectral ranges are calculated. We observe three x-ray bursts in X-pinch experiments with two Cu wires conducted on the SNU X-pinch at a current rise rate of ∼0.2 kA/ns. Analysis of the spectra reveals that the first burst comprises x-rays emitted by hot spots and electron beams, with characteristics similar to those observed in other X-pinches. The second and third bursts are both generated by long-lived electron beams formed after the neck structure has been completely depleted. In the second burst, the formation of the electron beam is accompanied by an increase in the electron density of the background plasma. Therefore, the long-lived electron beams generate the additional strong x-ray bursts while maintaining a plasma channel in the central region of the X-pinch. Moreover, they emit many hard x-rays (HXRs), enabling the SNU X-pinch to be used as an HXR source. This study confirms that the generation of long-lived electron beams is crucial to the dynamics of X-pinches and the generation of strong HXRs.
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Sato, K., K. Hirata, S. Singh, K. Kuga, F. Ogawa, M. Matsunami i T. Takeuchi. "Electronic structure of silver chalcogenides investigated by hard x-ray photoemission spectroscopy and density functional theory calculations". Journal of Applied Physics 132, nr 4 (28.07.2022): 045104. http://dx.doi.org/10.1063/5.0095987.
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We have investigated the electronic structure of silver chalcogenides Ag2 X ( X = S, Se, Te) and their solid solutions using hard x-ray photoemission spectroscopy in combination with density functional theory calculations using generalized gradient approximation (GGA). By including the corrections for on-site Coulomb interactions (GGA + U), we successfully reproduced the valence band photoemission spectra, which consist mainly of the Ag 4 d band, by calculation. The estimated values for U = 4–6 eV are slightly high for Ag 4 d electrons but are consistent with those used in previously reported structural studies. On the other hand, the magnitude of the energy gap is virtually independent of U. These results suggest the strong correlation between Ag 4 d electrons in Ag2 X compounds to have surprisingly little impact on their electron transport properties.
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Rodi, James, E. Jourdain i J. P. Roques. "MAXI J1535–571 2017 Outburst Seen by INTEGRAL/SPI and Investigating the Origin of Its Hard Tail". Astrophysical Journal 935, nr 1 (1.08.2022): 25. http://dx.doi.org/10.3847/1538-4357/ac7fff.
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Abstract On 2017 September 2 MAXI J1535–571 went into outburst and peaked at ∼5 Crab in the 2–20 keV energy range. Early in the flare, the INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL) performed target of opportunity pointings and monitored the source as it transitioned from the hard state to the soft state. Using quasi-simultaneous observations from MAXI/GSC and INTEGRAL/SPI, we studied the temporal and spectral evolution of MAXI J1535–571 in the 2–500 keV range. Early spectra show a Comptonized spectrum and a high-energy component dominant above ∼150 keV. CompTT fits to the SPectrometer on INTEGRAL (SPI) data found electron temperatures (kT e ) evolve from ∼31 keV to 18 keV with a tied optical depth (τ ∼ 0.85) or τ evolving from ∼1.2–0.65 with a tied kT e (∼24 keV). To investigate the nature of the high-energy component, we performed a spectral decomposition of the 100–400 keV energy band. The CompTT flux varies significantly during the hard state while the high-energy component flux is consistent with a constant flux. This result suggests that the two components originate from different locations, which favors a jet origin interpretation for the high-energy component over a hybrid corona interpretation. Lastly, two short rebrightenings during the hard-to-soft transition are compared to similar events reported in MAXI J1820+070.
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Sahakyan, N. "Investigation of the γ-ray spectrum of CTA 102 during the exceptional flaring state in 2016–2017". Astronomy & Astrophysics 635 (marzec 2020): A25. http://dx.doi.org/10.1051/0004-6361/201936715.
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The flat spectrum radio quasar CTA 102 entered an extended period of activity from 2016 to 2017 during which several strong γ-ray flares were observed. By using Fermi large area telescope data, a detailed investigation of γ-ray spectra of CTA 102 during the flaring period was performed. In several periods, the γ-ray spectrum is not consistent with a simple power-law, having a hard photon index with an index of ∼(1.8−2.0) that shows a spectral cut-off around an observed photon energy of ∼(9−16) GeV. The internal γ-ray absorption via photon-photon pair production on the broad-line-region-reflected photons cannot account for the observed cut-off and break even if the emitting region is very close to the central source. This cut-off and break are likely due to a similar intrinsic break in the energy distribution of emitting particles. The origin of the spectral break is investigated through the multiwavelength modeling of the spectral energy distribution in considering a different location for the emitting region. The observed X-ray and γ-ray data is modeled as inverse Compton scattering of synchrotron and/or external photons on the electron population that produces the radio-to-optical emission, which allowed to constrain the power-law index and cut-off energy in the electron energy distribution. The obtained results are discussed in the context of a diffusive acceleration of electrons in the CTA 102 jet.
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Bassi, T., J. Malzac, M. Del Santo, E. Jourdain, J.-P. Roques, A. D’Aì, J. C. A. Miller-Jones i in. "On the nature of the soft γ-ray emission in the hard state of the black hole transient GRS 1716−249". Monthly Notices of the Royal Astronomical Society 494, nr 1 (18.03.2020): 571–83. http://dx.doi.org/10.1093/mnras/staa739.
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ABSTRACT The black hole transient GRS 1716−249 was monitored from the radio to the γ-ray band during its 2016–2017 outburst. This paper focuses on the spectral energy distribution (SED) obtained in 2017 February–March, when GRS 1716−249 was in a bright hard spectral state. The soft γ-ray data collected with the INTEGRAL/SPI telescope show the presence of a spectral component that is in excess of the thermal Comptonization emission. This component is usually interpreted as inverse Compton emission from a tiny fraction of non-thermal electrons in the X-ray corona. We find that hybrid thermal/non-thermal Comptonization models provide a good fit to the X-/γ-ray spectrum of GRS 1716−249. The best-fitting parameters are typical of the bright hard state spectra observed in other black hole X-ray binaries. Moreover, the magnetized hybrid Comptonization model belm provides an upper limit on the intensity of the coronal magnetic field of about 106 G. Alternatively, this soft γ-ray emission could originate from synchrotron emission in the radio jet. In order to test this hypothesis, we fit the SED with the irradiated disc plus Comptonization model combined with the jet internal shock emission model ishem. We found that a jet with an electron distribution of p ≃ 2.1 can reproduce the soft γ-ray emission of GRS 1716−249. However, if we introduce the expected cooling break around 10 keV, the jet model can no longer explain the observed soft γ-ray emission, unless the index of the electron energy distribution is significantly harder (p < 2).
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Bhatta, Gopal, Maksym Mohorian i Illya Bilinsky. "Hard X-ray properties of NuSTAR blazars". Astronomy & Astrophysics 619 (listopad 2018): A93. http://dx.doi.org/10.1051/0004-6361/201833628.
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Context. Investigation of the hard X-ray emission properties of blazars is key to the understanding of the central engine of the sources and associated jet process. In particular, simultaneous spectral and timing analyses of the intraday hard X-ray observations provide us a means to peer into the compact innermost blazar regions that are not accessible to our current instruments. Aims. The primary objective of the work is to associate the observed hard X-ray variability properties in blazars with their flux and spectral states, thereby, based on the correlation among these states, extract the details about the emission regions and processes occurring near the central engine. Methods. We carried out timing, spectral, and cross-correlation analysis of 31 NuSTAR observations of 13 blazars. We investigated the spectral shapes of the sources using single power-law, broken power-law, and log-parabola models. We also studied the co-relation between the soft and hard emission using z-transformed discrete correlation function. In addition, we attempted to constrain the smallest emission regions using minimum variability timescales derived from the light curves. Results. We found that, for most of the sources, the hard X-ray emission can be well represented by the log-parabola model and that the spectral slopes for different blazar subclasses are consistent with the so-called blazar sequence. We also report the steepest spectra (Γ ∼ 3) in the BL Lacertae PKS 2155–304 and the hardest spectra (Γ ∼ 1.4) in the flat-spectrum radio quasar PKS 2149–306. In addition, we noted a close connection between the flux and spectral slope within the source subclass in the sense that high flux and/or flux states tend to be harder in spectra. In BL Lacertae objects, assuming particle acceleration by diffusive shocks and synchrotron cooling as the dominant processes governing the observed flux variability, we constrain the magnetic field of the emission region to be a few Gauss; whereas in flat-spectrum radio quasars, using external Compton models, we estimate the energy of the lower end of the injected electrons to be a few Lorentz factors.
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AGUI, AKANE, YUJI SAITOH, AKITAKA YOSHIGOE, TAKESHI NAKATANI, TOMOHIRO MATSUSHITA i MASAICHIRO MIZUMAKI. "HIGH ENERGY RESOLUTION MAGNETIC CIRCULAR DICHROISM MEASUREMENT OF THE FERRITE FAMILY". Surface Review and Letters 09, nr 02 (kwiecień 2002): 843–48. http://dx.doi.org/10.1142/s0218625x02003032.
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Magnetic circular dichroism (MCD) spectra of spinel ferrites MFe 2 O 4 (M = Co, Mn, Fe, Co and Ni) have been measured by using a photon-helicity-switching method. The method achieves high energy resolution and a low noise-to-signal ratio. The Fe L2,3 absorption spectra of MFe 2 O 4 show a similar spectral profile; on the other hand, the MCD spectra show the characteristic fine structures. These differences are attributed to the variety of 3d electron configuration of Fe ions ( Fe 2+ or Fe 3+) and the local symmetry (tetrahedral or octahedral). The origin of the positive peak of MFe 2 O 4 (M = Fe, Co and Ni) MCD spectra at the L3 edge is attributed to the tetrahedral Fe 3+ (3d5) state.
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Kalita, Nibedita, Alok C. Gupta i Minfeng Gu. "Temporal and Spectral Variability of OJ 287 before the April–June 2020 Outburst". Galaxies 8, nr 3 (6.08.2020): 58. http://dx.doi.org/10.3390/galaxies8030058.
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We present the results of a temporal and spectral study of the BL Lacertae object OJ 287 in optical, UV, and X-ray bands with observations performed by Swift satellite during September 2019–March 2020. In this period, the source showed moderate variability characterized by variability amplitude of ∼22–31% in all the wavelengths on a short timescale, except the hard X-ray band which was variable by only ∼8%. We observed that the X-ray flux of the source was significantly dominated by the soft photons below 2 keV. Soft lags of ∼45 days were detected between the optical/UV and soft X-ray emissions, while there is no correlation between the hard X-rays and the lower energy bands indicating the presence of two emission components or electron populations. Although two components contribute to the X-ray emission, most of the 0.3–10 keV spectra were well fitted with an absorbed power-law model which outlines the dominance of synchrotron over inverse Compton (IC) mechanism. The X-ray spectra follow a weak “softer when brighter” trend.
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Salvat-Pujol, Francesc, Roser Valentí i Wolfgang S. Werner. "Surface excitations in the modelling of electron transport for electron-beam-induced deposition experiments". Beilstein Journal of Nanotechnology 6 (3.06.2015): 1260–67. http://dx.doi.org/10.3762/bjnano.6.129.
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The aim of the present overview article is to raise awareness of an essential aspect that is usually not accounted for in the modelling of electron transport for focused-electron-beam-induced deposition (FEBID) of nanostructures: Surface excitations are on the one hand responsible for a sizeable fraction of the intensity in reflection-electron-energy-loss spectra for primary electron energies of up to a few kiloelectronvolts and, on the other hand, they play a key role in the emission of secondary electrons from solids, regardless of the primary energy. In this overview work we present a general perspective of recent works on the subject of surface excitations and on low-energy electron transport, highlighting the most relevant aspects for the modelling of electron transport in FEBID simulations.
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Kajava, J. J. E., S. E. Motta, C. Sánchez-Fernández i E. Kuulkers. "The December 2015 re-brightening of V404 Cygni". Astronomy & Astrophysics 616 (sierpień 2018): A129. http://dx.doi.org/10.1051/0004-6361/201731768.
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In December 2015 the black hole binary V404 Cyg underwent a secondary outburst after the main June 2015 event. We monitored this re-brightening with the INTEGRAL and Swift satellites, and in this paper we report the results of the time-resolved spectral analysis of these data. The December outburst shared several characteristics with the June event. The well-sampled INTEGRAL light curve shows up to ten Crab flares, which are separated by relatively weak non-flaring emission phases when compared to the June outburst. The spectra are nicely described by absorbed Comptonization models, with hard photon indices, Γ ≲ 2, and significant detections of a high-energy cut-off only during the bright flares. This is in contrast to the June outburst, where the Comptonization models gave electron temperatures mostly in the 30–50 keV range, while some spectra were soft (Γ ~ 2.5) without signs of any spectral cut-off. Similarly to the June outburst, we see clear signs of a variable local absorber in the soft energy band covered by Swift/XRT and INTEGRAL/JEM-X, which causes rapid spectral variations observed during the flares. During one flare, both Swift and INTEGRAL captured V404 Cyg in a state where the absorber was nearly Compton thick, N H ≈ 1024 cm−2, and the broad-band spectrum was similar to obscured AGN spectra, as seen during the X-ray plateaus in the June outburst. We conclude that the spectral behaviour of V404 Cyg during the December outburst was analogous with the first few days of the June outburst, both having hard X-ray flares that were intermittently influenced by obscuration due to nearly Compton-thick outflows launched from the accretion disc.
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Sapienza, Vincenzo, Marco Miceli, Aya Bamba, Satoru Katsuda, Tsutomu Nagayoshi, Yukikatsu Terada, Fabrizio Bocchino, Salvatore Orlando i Giovanni Peres. "A Spatially Resolved Study of Hard X-Ray Emission in Kepler’s Supernova Remnant: Indications of Different Regimes of Particle Acceleration". Astrophysical Journal 935, nr 2 (1.08.2022): 152. http://dx.doi.org/10.3847/1538-4357/ac8160.
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Abstract Synchrotron X-ray emission in young supernova remnants (SNRs) is a powerful diagnostic tool to study the population of high-energy electrons accelerated at the shock front and the acceleration process. We performed a spatially resolved spectral analysis of NuSTAR and XMM-Newton observations of the young Kepler’s SNR, aiming to study in detail its nonthermal emission in hard X-rays. We selected a set of regions all around the rim of the shell and extracted the corresponding spectra. The spectra were analyzed by adopting a model of synchrotron radiation in the loss-limited regime, to constrain the dependence of the cutoff energy of the synchrotron radiation on the shock velocity. We identify two different regimes of particle acceleration, characterized by different Bohm factors. In the north, where the shock interacts with a dense circumstellar medium (CSM), we found a more efficient acceleration than in the south, where the shock velocity is higher and there are no signs of shock interaction with the dense CSM. Our results suggest an enhanced efficiency of the acceleration process in regions where the shock–CSM interaction generates an amplified and turbulent magnetic field. By combining hard X-ray spectra with radio and γ-ray observations of Kepler’s SNR, we modeled the spectral energy distribution. In the light of our results we propose that the observed γ-ray emission is mainly hadronic and originates in the northern part of the shell.
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Liu, J., P. A. Crozier, G. G. Hembree, F. C. H. Luo, J. M. Cowley i J. A. Venables. "Variations in Secondary Electron Emission from MgO Characterized by Secondary Electron Spectroscopy". Proceedings, annual meeting, Electron Microscopy Society of America 48, nr 1 (12.08.1990): 336–37. http://dx.doi.org/10.1017/s0424820100180434.
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The recent developments of the in-lens field emission scanning electron microscopes make it possible to image specimen surfaces with subnanometer resolution by collecting high resolution type I secondary electron (SE) signals. SE images with a resolutiori better than 1 nm have also been obtained in scanning transmission electron microscope (STEM) instruments. A problem related to the correct interpretation of these high resolution images is the lack of knowledge on the energies of the collected electrons contributing to the images. On the other hand secondary electron spectroscopy (SES) on clean surfaces has been developed for several years and biased SE imaging of several deposits on metallic and semiconductor crystal surfaces has been demonstrated. The combination of ultra-high resolution SE imaging with SES and Auger electron spectroscopy (AES) can be realized in pur UHV STEM instrument (MIDAS). The description of the performance of the MIDAS is reported elsewhere. We report here some recent results on SE imaging of MgO smoke crystals, in the MIDAS, with energy analysis of the collected secondary electrons.Strong variations of SE signals from different MgO crystals have been observed and the intensity of the collected secondary electrons from some MgO cubes increases under electron beam irradiation. Figure 1 shows a SE image of several MgO cubes, revealing that some of the crystals (indicated by A) have much higher intensity than others (indicated by B) and bright diffuse patches on the dark crystal can be seen (indicated by D). We have used SES to study the variations in SE emission under electron irradiation. The fact that the velocity distribution of the emitted secondary electrons may depend strongly on the surface morphology of the samples studied makes the interpretation of these SE spectra complicated. In order to avoid this problem and other possible complications arising from the detector geometry we acquired SE spectra from a fixed flat area of a single crystal MgO shown in figure 2. The sample was biased at -30 V and the resolution of the SE spectrum is about 1 eV. Figure 3a shows the SE spectra, taken from the exit surface of the crystal. Spectrum 1 was obtained from a poorly emitting MgO cube as that shown in figure 2 (all the spectra were obtained from the circled area). Spectra 2, 3 and 4 were obtained after about 10, 20 and 40 minutes electron irradiation respectively. In order to study spectral shape variations the spectra were normalized so that they all had the same peak intensity. The normalized data were shown in figure 3b.
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Melrose, D. B. "The Nature of Flat Spectrum Sources". Symposium - International Astronomical Union 175 (1996): 423–26. http://dx.doi.org/10.1017/s0074180900081328.
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Nonthermal radio sources near the Galactic Center with flat or weakly inverted spectra (S((ω) ∝ ωα with α ≳ 0) are attributed to optically thin synchrotron emission from a hard electron energy spectrum, N(ε) ∝ ε–α with a = 1 – 2α ≲ 1, produced by Fermi acceleration or diffusive shock acceleration at multiple shocks combined with a synchrotron pile up. This basic mechanism is also plausible for flat-spectrum AGN.
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Banerjee, Srimanta, Marat Gilfanov, Sudip Bhattacharyya i Rashid Sunyaev. "Observing imprints of black hole event horizon on X-ray spectra". Monthly Notices of the Royal Astronomical Society 498, nr 4 (25.09.2020): 5353–60. http://dx.doi.org/10.1093/mnras/staa2788.
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ABSTRACT A fundamental difference between a neutron star (NS) and a black hole (BH) is the absence of a physical surface in the latter. For this reason, any remaining kinetic energy of the matter accreting on to a BH is advected inside its event horizon. In the case of an NS, on the contrary, accreting material is decelerated on the NS surface, and its kinetic energy is eventually radiated away. Copious soft photons produced by the NS surface will affect the properties of the Comptonized component dominating spectra of X-ray binaries in the hard state. Thus, parameters of the Comptonized spectra – the electron temperature kTe and the Compton y-parameter, could serve as an important tool for distinguishing BHs from NSs. In this paper, we systematically analyse heretofore the largest sample of spectra from the BH and NS X-ray binaries in the hard state for this purpose, using archival RXTE/PCA and RXTE/HEXTE observations. We find that the BHs and NSs occupy distinctly different regions in the y − kTe plane with NSs being characterized by systematically lower values of y-parameter and electron temperature. Due to the shape of the boundary between BHs and NSs on the y − kTe plane, their 1D y and kTe distributions have some overlap. A cleaner one parameter diagnostic of the nature of the compact object in X-ray binaries is provided by the Compton amplification factor A, with the boundary between BHs and NSs lying at A ≈ 3.5–4. This is by far the most significant detection of the imprint of the event horizon on the X-ray spectra for stable stellar-mass BHs.
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Ding, G. Q., J. L. Qu, L. M. Song, Y. Huang, S. Zhang, Q. C. Bu, M. Y. Ge i in. "Insight-HXMT Detections of Hard X-Ray Tails in Scorpius X-1". Astrophysical Journal 950, nr 1 (1.06.2023): 69. http://dx.doi.org/10.3847/1538-4357/accf91.
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Abstract 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.
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Kong, Xiangliang, Bin Chen, Fan Guo, Chengcai Shen, Xiaocan Li, Jing Ye, Lulu Zhao i in. "Numerical Modeling of Energetic Electron Acceleration, Transport, and Emission in Solar Flares: Connecting Loop-top and Footpoint Hard X-Ray Sources". Astrophysical Journal Letters 941, nr 2 (1.12.2022): L22. http://dx.doi.org/10.3847/2041-8213/aca65c.
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Abstract The acceleration and transport of energetic electrons during solar flares is one of the outstanding topics in solar physics. Recent X-ray and radio imaging and spectroscopy observations have provided diagnostics of the distribution of nonthermal electrons and suggested that, in certain flare events, electrons are primarily accelerated in the loop top and likely experience trapping and/or scattering effects. By combining the focused particle transport equation with magnetohydrodynamic (MHD) simulations of solar flares, we present a macroscopic particle model that naturally incorporates electron acceleration and transport. Our simulation results indicate that physical processes such as turbulent pitch-angle scattering can have important impacts on both electron acceleration in the loop top and transport in the flare loop, and their influences are highly energy-dependent. A spatial-dependent turbulent scattering with enhancement in the loop top can enable both efficient electron acceleration to high energies and transport of abundant electrons to the footpoints. We further generate spatially resolved synthetic hard X-ray (HXR) emission images and spectra, revealing both the loop-top and footpoint HXR sources. Similar to the observations, we show that the footpoint HXR sources are brighter and harder than the loop-top HXR source. We suggest that the macroscopic particle model provides new insights into understanding the connection between the observed loop-top and footpoint nonthermal emission sources by combining the particle model with dynamically evolving MHD simulations of solar flares.
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Done, C., i A. C. Fabian. "Pair Production in AGN". Symposium - International Astronomical Union 134 (1989): 194–96. http://dx.doi.org/10.1017/s007418090014080x.
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The X-ray luminosity and variability of many AGN are sufficiently extreme that any hard γ-rays produced in the source will collide with the X-rays and create electron-positron pairs, rather than escape. A small region where vast amounts of energy are produced, such as an AGN, is an ideal place to accelerate particles to relativistic energies and so produce γ-rays by Compton scattering. The observed X-ray spectra of AGN are hard and indicate that most of the luminosity is at the highest energies so that absorption of the γ-rays represents a large fraction of the energy flux, which can then be re-radiated at lower energies. Pairs can thus effectively reprocess much of the radiant power in an AGN.
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Kong, Xiangliang, Jing Ye, Bin Chen, Fan Guo, Chengcai Shen, Xiaocan Li, Sijie Yu, Yao Chen i Joe Giacalone. "A Model of Double Coronal Hard X-Ray Sources in Solar Flares". Astrophysical Journal 933, nr 1 (1.07.2022): 93. http://dx.doi.org/10.3847/1538-4357/ac731b.
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Abstract A number of double coronal X-ray sources have been observed during solar flares by RHESSI, where the two sources reside at different sides of the inferred reconnection site. However, where and how these X-ray-emitting electrons are accelerated remains unclear. Here we present the first model of the double coronal hard X-ray (HXR) sources, where electrons are accelerated by a pair of termination shocks driven by bidirectional fast reconnection outflows. We model the acceleration and transport of electrons in the flare region by numerically solving the Parker transport equation using velocity and magnetic fields from the macroscopic magnetohydrodynamic simulation of a flux rope eruption. We show that electrons can be efficiently accelerated by the termination shocks and high-energy electrons mainly concentrate around the two shocks. The synthetic HXR emission images display two distinct sources extending to >100 keV below and above the reconnection region, with the upper source much fainter than the lower one. The HXR energy spectra of the two coronal sources show similar spectral slopes, consistent with the observations. Our simulation results suggest that the flare termination shock can be a promising particle acceleration mechanism in explaining the double-source nonthermal emissions in solar flares.
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Lützenkirchen-Hecht, D., R. Wagner, S. Szillat, A. K. Hüsecken, K. Istomin, U. Pietsch i Ronald Frahm. "The multi-purpose hard X-ray beamline BL10 at the DELTA storage ring". Journal of Synchrotron Radiation 21, nr 4 (13.05.2014): 819–26. http://dx.doi.org/10.1107/s1600577514006705.
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The layout and the characteristics of the hard X-ray beamline BL10 at the superconducting asymmetric wiggler at the 1.5 GeV Dortmund Electron Accelerator DELTA are described. This beamline is equipped with a Si(111) channel-cut monochromator and is dedicated to X-ray studies in the spectral range from ∼4 keV to ∼16 keV photon energy. There are two different endstations available. While X-ray absorption studies in different detection modes (transmission, fluorescence, reflectivity) can be performed on a designated table, a six-axis kappa diffractometer is installed for X-ray scattering and reflectivity experiments. Different detector set-ups are integrated into the beamline control software,i.e.gas-filled ionization chambers, different photodiodes, as well as a Pilatus 2D-detector are permanently available. The performance of the beamline is illustrated by high-quality X-ray absorption spectra from several reference compounds. First applications include temperature-dependent EXAFS experiments from liquid-nitrogen temperature in a bath cryostat up to ∼660 K by using a dedicated furnace. Besides transmission measurements, fluorescence detection for dilute sample systems as well as surface-sensitive reflection-mode experiments are presented.
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Cheng, Shikui, Jie Zhang, Yipo Zhang, Li He, Hongbing Xu, Yuxuan Zhu, Xuwen Zhan, Zhongbing Shi i Wulv Zhong. "Development of hard X-ray spectrometer with full digital data acquisition for runaway electron studies at HL-2M". Journal of Instrumentation 18, nr 02 (1.02.2023): T02006. http://dx.doi.org/10.1088/1748-0221/18/02/t02006.
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Abstract The development of hard X-ray (HXR) spectrometers with full digital data acquisition for runaway electron studies on the HL-2M tokamak is presented. Consisting of large-sized NaI:Tl detectors and high-performance multichannel analyzers, this system can realize the measurement of HXR with energies ranging from 0.5 to 10 MeV, and spectrum temporal resolution of 1 ms. An average energy resolution of 56 keV at 662 keV has been achieved at counts rates of about 100 kcps. The spectra data is acquired by a digital-based data acquisition system with fast digitization and software signal processing technology. The energy calibrations are performed by using several radioisotope gamma-ray sources, and the detection efficiencies are simulated by MCNP code. First experimental results from HL-2M Ohmic discharges are presented in this paper.
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Samoylova, Liubov, Ulrike Boesenberg, Aleksandr Chumakov, Vladimir Kaganer, Ilia Petrov, Thomas Roth, Rudolf Rüffer, Harald Sinn, Sergey Terentyev i Anders Madsen. "Diffraction properties of a strongly bent diamond crystal used as a dispersive spectrometer for XFEL pulses". Journal of Synchrotron Radiation 26, nr 4 (6.06.2019): 1069–72. http://dx.doi.org/10.1107/s1600577519004880.
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Self-amplified spontaneous emission (SASE) enables X-ray free-electron lasers (XFELs) to generate hard X-ray pulses of sub-100 fs duration. However, due to the stochastic nature of SASE, the energy spectrum fluctuates from pulse to pulse. Many experiments that employ XFEL radiation require the resolution of the spectrum of each pulse. The work presented here investigates the capacity of a thin strongly bent diamond crystal to resolve the energy spectra of hard X-ray SASE pulses by studying its diffraction properties. Rocking curves of the symmetric C*(440) reflection have been measured for different bending radii. The experimental data match the theoretical modelling based on the Takagi–Taupin equations of dynamical diffraction. A uniform strain gradient has proven to be a valid model of strain deformations in the crystal.
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Varga, L., i D. Venkatesan. "Detection of very soft X-ray spectra by balloon-borne detectors". Canadian Journal of Physics 69, nr 8-9 (1.08.1991): 999–1006. http://dx.doi.org/10.1139/p91-158.
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A balloon payload launched from Cold Lake, Alta., Canada, on October 14, 1982, measured the spectrum of X rays (E = 20–160 keV) with a hard and a very soft component. The latter contributes significantly only to the 20–40 keV channel; thus a "flapping motion" at the lower energy end of the composite spectrum is observed. We have simulated, using the Monte-Carlo technique, the propagation of X rays through the atmosphere and determined the e-folding energy of the very soft component, which we estimate to be 5 keV, at a particular time (10:45 UT). The electron spectrum producing this soft X-ray source agrees well with in situ satellite and rocket-borne measurements of electron spectra during active auroras. Simulataneous auroral optical emissions (5577 Å (1 Å = 10−10 m)) by a ground-based all-sky charge-coupled device camera are also available for comparison. We also determine the count rate ratio between 20–40 and 60–80 keV channels as a parameter of the variability of the intensity of the very soft component. The time-changes of this ratio and that of the auroral optical emission intensity near the vicinity of the balloon are correlated. The lack of correlation at some other times is ascribed to differences in the behavior of the low- and high-energy ends of the elecron spectrum.
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Ahnen, M. L., S. Ansoldi, L. A. Antonelli, C. Arcaro, A. Babić, B. Banerjee, P. Bangale i in. "Extreme HBL behavior of Markarian 501 during 2012". Astronomy & Astrophysics 620 (grudzień 2018): A181. http://dx.doi.org/10.1051/0004-6361/201833704.
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Aims. We aim to characterize the multiwavelength emission from Markarian 501 (Mrk 501), quantify the energy-dependent variability, study the potential multiband correlations, and describe the temporal evolution of the broadband emission within leptonic theoretical scenarios. Methods. We organized a multiwavelength campaign to take place between March and July of 2012. Excellent temporal coverage was obtained with more than 25 instruments, including the MAGIC, FACT and VERITAS Cherenkov telescopes, the instruments on board the Swift and Fermi spacecraft, and the telescopes operated by the GASP-WEBT collaboration. Results. Mrk 501 showed a very high energy (VHE) gamma-ray flux above 0.2 TeV of ∼0.5 times the Crab Nebula flux (CU) for most of the campaign. The highest activity occurred on 2012 June 9, when the VHE flux was ∼3 CU, and the peak of the high-energy spectral component was found to be at ∼2 TeV. Both the X-ray and VHE gamma-ray spectral slopes were measured to be extremely hard, with spectral indices < 2 during most of the observing campaign, regardless of the X-ray and VHE flux. This study reports the hardest Mrk 501 VHE spectra measured to date. The fractional variability was found to increase with energy, with the highest variability occurring at VHE. Using the complete data set, we found correlation between the X-ray and VHE bands; however, if the June 9 flare is excluded, the correlation disappears (significance < 3σ) despite the existence of substantial variability in the X-ray and VHE bands throughout the campaign. Conclusions. The unprecedentedly hard X-ray and VHE spectra measured imply that their low- and high-energy components peaked above 5 keV and 0.5 TeV, respectively, during a large fraction of the observing campaign, and hence that Mrk 501 behaved like an extreme high-frequency-peaked blazar (EHBL) throughout the 2012 observing season. This suggests that being an EHBL may not be a permanent characteristic of a blazar, but rather a state which may change over time. The data set acquired shows that the broadband spectral energy distribution (SED) of Mrk 501, and its transient evolution, is very complex, requiring, within the framework of synchrotron self-Compton (SSC) models, various emission regions for a satisfactory description. Nevertheless the one-zone SSC scenario can successfully describe the segments of the SED where most energy is emitted, with a significant correlation between the electron energy density and the VHE gamma-ray activity, suggesting that most of the variability may be explained by the injection of high-energy electrons. The one-zone SSC scenario used reproduces the behavior seen between the measured X-ray and VHE gamma-ray fluxes, and predicts that the correlation becomes stronger with increasing energy of the X-rays.
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Ageeva, E. V., i B. N. Sabel’nikov. "X-RAY SPECTRAL MICROANALYSIS OF ELECTROEROSIVE POWDER MATERIAL OBTAINED IN AN ETHYL ALCOHOL MEDIUM FROM WASTE OF A NON-TUNGSTEN HARD ALLOY OF THE KNT16 BRAND". IZVESTIA VOLGOGRAD STATE TECHNICAL UNIVERSITY, nr 7(242) (29.07.2020): 33–36. http://dx.doi.org/10.35211/1990-5297-2020-7-242-33-36.
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The first appearance of tungsten-free hard alloys (TFHA) was noted in the early 30s of the last century, but they did not receive due attention and, accordingly, spread due to insufficient strength and were replaced by tungsten-containing alloys of such groups as VK, TC and TTK. However, the rapidly developing shortage of expensive tungsten pushed in the late 50s to return to the search for hard alloys, the composition of which does not include tungsten. Due to the growing demand for tungsten-free hard alloys, the problem of recycling their waste with the possibility of reuse is acute in the industry. The purpose of this work was to conduct x-ray spectral microanalysis (RSMA) of powder material (PM) obtained by electroerosive dispersion (EED) in ethyl alcohol from waste of a non-tungsten hard alloy of the KNT16 brand. The resulting powder material was examined using an energy-dispersion x-ray analyzer from EDAX, built into a scanning electron microscope "QUANTA 600 FEG". In the course of scientific research, the spectra of characteristic x-ray radiation on the surface of the experimentally obtained sample were obtained. The results obtained in the course of scientific research can be used to create environmentally friendly resource-saving processes for processing waste of tungsten-free hard alloys into powder materials.
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Rich, David, Diling Zhu, James Turner, Dehong Zhang, Bruce Hill i Yiping Feng. "The LCLS variable-energy hard X-ray single-shot spectrometer". Journal of Synchrotron Radiation 23, nr 1 (1.01.2016): 3–9. http://dx.doi.org/10.1107/s1600577515022559.
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The engineering design, implementation, operation and performance of the new variable-energy hard X-ray single-shot spectrometer (HXSSS) for the LCLS free-electron laser (FEL) are reported. The HXSSS system is based on a cylindrically bent Si thin crystal for dispersing the incident polychromatic FEL beam. A spatially resolved detector system consisting of a Ce:YAG X-ray scintillator screen, an optical imaging system and a low-noise pixelated optical camera is used to record the spectrograph. The HXSSS provides single-shot spectrum measurements for users whose experiments depend critically on the knowledge of the self-amplified spontaneous emission FEL spectrum. It also helps accelerator physicists for the continuing studies and optimization of self-seeding, various improved mechanisms for lasing mechanisms, and FEL performance improvements. The designed operating energy range of the HXSSS is from 4 to 20 keV, with the spectral range of order larger than 2% and a spectral resolution of 2 × 10−5or better. Those performance goals have all been achieved during the commissioning of the HXSSS.
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Zdziarski, A. A. "Radiative Processes and Geometry of Spectral States of Black-hole Binaries". Symposium - International Astronomical Union 195 (2000): 153–70. http://dx.doi.org/10.1017/s0074180900162898.
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I review radiative processes responsible for X-ray emission in the hard (low) and soft (high) spectral states of black-hole binaries. The main process in the hard state appears to be thermal Comptonization (in a hot plasma) of blackbody photons emitted by a cold disk. This is supported by correlations between the spectral index, the strength of Compton reflection, and the peak frequencies in the power-density spectrum, as well as by the frequency-dependence of Fourier-resolved spectra. Spectral variability may then be driven by the variable truncation radius of the disk. The soft state appears to correspond to the smallest truncation radii. However, the lack of high-energy cutoffs observed in the soft state implies that its main radiative process is Compton scattering of disk photons by nonthermal electrons. The bulk-motion Comptonization model for the soft state is shown to be ruled out by the data.
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Laksman, Joakim, Florian Dietrich, Jia Liu, Theophilos Maltezopoulos, Marc Planas, Wolfgang Freund, Randeer Gautam, Naresh Kujala, Sonia Francoual i Jan Grünert. "Development of a photoelectron spectrometer for hard x-ray photon diagnostics". Review of Scientific Instruments 93, nr 11 (1.11.2022): 115111. http://dx.doi.org/10.1063/5.0097525.
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The development and characterization of an angle-resolved photoelectron spectrometer, based on the electron time-of-flight concept, for hard x-ray photon diagnostics at the European Free-Electron Laser, are described. The instrument is meant to provide users and operators with pulse-resolved, non-invasive spectral distribution diagnostics, which in the hard x-ray regime is a challenge due to the poor cross-section and high kinetic energy of photoelectrons for the available target gases. We report on the performances of this instrument as obtained using hard x-rays at the PETRA III synchrotron at DESY in multibunch mode. Results are compared with electron trajectory simulations. We demonstrate a resolving power of 10 eV at incident photon energies up to at least 20 keV.
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David, Christian, Gediminas Seniutinas, Mikako Makita, Benedikt Rösner, Jens Rehanek, Petri Karvinen, Florian Löhl, Rafael Abela, Luc Patthey i Pavle Juranić. "Spectral monitoring at SwissFEL using a high-resolution on-line hard X-ray single-shot spectrometer". Journal of Synchrotron Radiation 28, nr 6 (21.10.2021): 1978–84. http://dx.doi.org/10.1107/s1600577521009619.
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The performance and parameters of the online photon single-shot spectrometer (PSSS) at the Aramis beamline of the SwissFEL free-electron laser are presented. The device operates between the photon energies 4 and 13 keV and uses diamond transmission gratings and bent Si crystals for spectral measurements on the first diffraction order of the beam. The device has an energy window of 0.7% of the median photon energy of the free-electron laser pulses and a spectral resolution (full width at half-maximum) ΔE/E on the order of 10−5. The device was characterized by comparing its performance with reference data from synchrotron sources, and a parametric study investigated other effects that could affect the reliability of the spectral information.
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Rieger, E. "Gamma-Ray Precursors of Solar Flares". International Astronomical Union Colloquium 142 (1994): 645–48. http://dx.doi.org/10.1017/s0252921100077927.
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AbstractBursts have been observed by the gamma-ray spectrometer on SMM at medium- and high-energy gamma-rays that precede the flare maximum. The negligible contribution of nuclear lines in the spectra of these events and their impulsive appearance suggests that they are hard-electron-dominated events superposed on the flares. Spatial resolution at gamma-ray energies will be necessary to decide whether this kind of bursts is cospatial with the flares or whether they occur in the flares’ vicinity.Subject headings: Sun: flares — Sun: X-rays, gamma rays
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Sobacchi, Emanuele, Lorenzo Sironi i Andrei M. Beloborodov. "Synchrotron self-Compton radiation from magnetically dominated turbulent plasmas in relativistic jets". Monthly Notices of the Royal Astronomical Society 506, nr 1 (14.06.2021): 38–51. http://dx.doi.org/10.1093/mnras/stab1702.
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ABSTRACT Relativistic jets launched by rotating black holes are powerful emitters of non-thermal radiation. Extraction of the rotational energy via electromagnetic stresses produces magnetically dominated jets, which may become turbulent. Studies of magnetically dominated plasma turbulence from first principles show that most of the accelerated particles have small pitch angles, i.e. the particle velocity is nearly aligned with the local magnetic field. We examine synchrotron self-Compton radiation from anisotropic particles in the fast cooling regime. The small pitch angles reduce the synchrotron cooling rate and promote the role of inverse Compton (IC) cooling, which can occur in two different regimes. In the Thomson regime, both synchrotron and IC components have soft spectra, νFν ∝ ν1/2. In the Klein–Nishina regime, synchrotron radiation has a hard spectrum, typically νFν ∝ ν, over a broad range of frequencies. Our results have implications for the modelling of BL Lacertae objects (BL Lacs) and gamma-ray bursts (GRBs). BL Lacs produce soft synchrotron and IC spectra, as expected when Klein–Nishina effects are minor. The observed synchrotron and IC luminosities are typically comparable, which indicates a moderate anisotropy with pitch angles θ ≳ 0.1. Rare orphan gamma-ray flares may be produced when θ ≪ 0.1. The hard spectra of GRBs may be consistent with synchrotron radiation when the emitting particles are IC cooling in the Klein–Nishina regime, as expected for pitch angles θ ∼ 0.1. Blazar and GRB spectra can be explained by turbulent jets with a similar electron plasma magnetization parameter, σe ∼ 104, which for electron–proton plasmas corresponds to an overall magnetization σ = (me/mp)σe ∼ 10.
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Petrillo, Vittoria, Illya Drebot, Geoffrey Krafft, Cesare Maroli, Andrea R. Rossi, Marcello Rossetti Rossetti Conti, Marcel Ruijter i Balša Terzić. "A Laser Frequency Transverse Modulation Might Compensate for the Spectral Broadening Due to Large Electron Energy Spread in Thomson Sources". Photonics 9, nr 2 (25.01.2022): 62. http://dx.doi.org/10.3390/photonics9020062.
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Compact laser plasma accelerators generate high-energy electron beams with increasing quality. When used in inverse Compton backscattering, however, the relatively large electron energy spread jeopardizes potential applications requiring small bandwidths. We present here a novel interaction scheme that allows us to compensate for the negative effects of the electron energy spread on the spectrum, by introducing a transverse spatial frequency modulation in the laser pulse. Such a laser chirp, together with a properly dispersed electron beam, can substantially reduce the broadening of the Compton bandwidth due to the electron energy spread. We show theoretical analysis and numerical simulations for hard X-ray Thomson sources based on laser plasma accelerators.
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Numazawa, Masaki, Yuichiro Ezoe, Takaya Ohashi, Kumi Ishikawa, Yoshizumi Miyoshi, Daikou Shiota, Yasunobu Uchiyama, Tomoki Kimura i Graziella Branduardi-Raymont. "Suzaku observations of Jovian diffuse hard X-ray emission". Publications of the Astronomical Society of Japan 73, nr 4 (9.06.2021): 894–911. http://dx.doi.org/10.1093/pasj/psab053.
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Abstract We report on results of systematic analyses of the entire three X-ray data sets of Jupiter taken by Suzaku in 2006, 2012, and 2014. Jovian diffuse hard X-ray emission was discovered by Suzaku in 2006 when the solar activity went toward its minimum. The diffuse emission was spatially consistent with the Jovian inner magnetosphere and was spectrally fitted with a flat power-law function suggesting non-thermal emission. Thus, a scenario in which ultra-relativistic (tens of MeV) electrons in the Jovian inner magnetosphere inverse-Comptonize solar visible photons into X-ray bands has been hypothetically proposed. We focused on the dependence of the Jovian diffuse hard X-ray emission on the solar activity to verify this scenario. The solar activity in 2012 and 2014 was around the maximum of the 24th solar cycle. By combining the imaging and spectral analyses for the three data sets, we successfully separated the contribution of the diffuse emission from the emission of Jupiter’s body (i.e., the aurora and disk emission). The 1–5 keV luminosity of the diffuse emission has been stable and did not vary significantly, and did not simply depend on the solar activity, which is also known to affect the high-energy electron distribution in the Jovian inner magnetosphere scarcely. The luminosity of the body emission both in 0.2–1 and 1–5 keV, in contrast, probably depended on the solar activity and varied by a factor of 2–5. These results strongly supported the inverse-Compton scattering scenario by the ultra-relativistic electrons. In this paper, we estimate spatial and spectral distributions of the inverse-Compton scattering X-rays by Jovian magnetospheric high-energy electrons with reference to the Divine–Garrett model and found a possible agreement in an inner region (≲10 RJ) for the X-ray observations.
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Lei, Maichang, Yuan Zheng, Jianfu Zhang i Jiancheng Wang. "Explaining the Multiwavelength Emission of Hard-TeV BL Lac Objects Using a Truncated Conical Jet Model". Research in Astronomy and Astrophysics 22, nr 4 (17.03.2022): 045005. http://dx.doi.org/10.1088/1674-4527/ac501e.
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Abstract Hard-TeV BL Lac objects are newly identified populations of active galactic nuclei with the emitted γ-ray photons well above TeV energies. In this paper, we explain the multiwavelength emission of six Hard-TeV BL Lac objects by using a truncated conical emission region of the jet, where the electron distribution is obtained by numerically solving the evolution equation along the jet self-consistently. For comparison, we also apply the model to Mrk 421 and Mrk 501, which are the potential candidates for the hard TeV emissions. We demonstrate that the model can satisfactorily reproduce the spectral energy distributions of eight sources, particularly of six Hard-TeV sources, where no extreme minimum Lorentz factor of the electron population is required. In contrast with Mrk 421 and Mrk 501, six Hard-TeV sources have rather low magnetization in emitting regions and high cutoff energies of the electron distributions.
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Van Oss, R. F., G. H. J. Van Den Oord i M. Kuperus. "Accretion Disk Flares in Energetic Radiation Fields". Symposium - International Astronomical Union 157 (1993): 217–18. http://dx.doi.org/10.1017/s0074180900174157.
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We consider the physics of magnetic flares in the energetic radiation field of an accretion disk corona (ADC). The X-ray emission from these flares is thought to be responsable for the observed hard powerlaw component in the X-ray spectra of galactic black hole candidates in their ‘high’ spectral state. During the flare event (inverse Compton) scattering of soft photons from the underlying disk into hard photons occurs on accelerated electrons in current sheets. The electrons are decelerated by the radiation drag force that results from the up-scattering. This friction-like effect of the intense background radiation field on the motion of the electrons in the sheet can be considered as a form of resistivity in the magnetohydrodynamical picture of the current sheet: Compton resistivity. A spectrum is derived for the up-scattered radiation from current sheets in the ADC and it is found that this spectrum mimics a powerlaw above a critical photon energy.
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Panontin, E., A. Dal Molin, M. Nocente, G. Croci, J. Eriksson, L. Giacomelli, G. Gorini i in. "Comparison of unfolding methods for the inference of runaway electron energy distribution from γ-ray spectroscopic measurements". Journal of Instrumentation 16, nr 12 (1.12.2021): C12005. http://dx.doi.org/10.1088/1748-0221/16/12/c12005.
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Abstract Unfolding techniques are employed to reconstruct the 1D energy distribution of runaway electrons from Bremsstrahlung hard X-ray spectrum emitted during plasma disruptions in tokamaks. Here we compare four inversion methods: truncated singular value decomposition, which is a linear algebra technique, maximum likelihood expectation maximization, which is an iterative method, and Tikhonov regularization applied to χ 2 and Poisson statistics, which are two minimization approaches. The reconstruction fidelity and the capability of estimating cumulative statistics, such as the mean and maximum energy, have been assessed on both synthetic and experimental spectra. The effect of measurements limitations, such as the low energy cut and few number of counts, on the final reconstruction has also been studied. We find that the iterative method performs best as it better describes the statistics of the experimental data and is more robust to noise in the recorded spectrum.
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Poutanen, Juri, Alexandra Veledina i Andrzej A. Zdziarski. "Doughnut strikes sandwich: the geometry of hot medium in accreting black hole X-ray binaries". Astronomy & Astrophysics 614 (czerwiec 2018): A79. http://dx.doi.org/10.1051/0004-6361/201732345.
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We study the effects of the mutual interaction of hot plasma and cold medium in black hole binaries in their hard spectral state. We consider a number of different geometries. In contrast to previous theoretical studies, we use a modern energy-conserving code for reflection and reprocessing from cold media. We show that a static corona above an accretion disc extending to the innermost stable circular orbit produces spectra not compatible with those observed. They are either too soft or require a much higher disc ionization than that observed. This conclusion confirms a number of previous findings, but disproves a recent study claiming an agreement of that model with observations. We show that the cold disc has to be truncated in order to agree with the observed spectral hardness. However, a cold disc truncated at a large radius and replaced by a hot flow produces spectra which are too hard if the only source of seed photons for Comptonization is the accretion disc. Our favourable geometry is a truncated disc coexisting with a hot plasma either overlapping with the disc or containing some cold matter within it, also including seed photons arising from cyclo-synchrotron emission of hybrid electrons, i.e. containing both thermal and non-thermal parts.
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Huotari, Simo. "X-ray Raman scattering spectroscopy". Acta Crystallographica Section A Foundations and Advances 70, a1 (5.08.2014): C219. http://dx.doi.org/10.1107/s2053273314097800.
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For elements with low atomic number, or shallow absorption edges falling in the energy range below ~1 keV, x-ray absorption studies are often limited by surface sensitivity and the necessity of a vacuum environment, making bulk-sensitive measurements and for example studies of liquids difficult. An exciting alternative is provided by X-ray Raman scattering (XRS) spectroscopy. It is used to measure a photon-in-photon-out process, where a hard x-ray photon loses only part of its energy creating an excitation of an inner core electron. As such, it is the x-ray analogue of electron energy loss spectroscopy. The advantage of XRS is that the incident photon energy can be chosen freely and thus low-energy absorption edges can be studied with high-energy X-rays. Thus XRS is becoming increasingly popular since it allows for bulk-sensitive measurements of inner core spectra where the corresponding x-ray absorption threshold falls into the soft x-ray regime. This lifts all constraints on the sample environment inherent to soft x-ray studies, and offers access to bulk-sensitive information on solids, liquids and gases as well as systems in enclosed sample environments such as high-pressure cells. For example the microscopic structure of water within the supercritical regime has been recently studied using the oxygen K-edge excitation spectra measured by XRS, yielding new information on the hydrogen-bond network of water in extreme conditions [1]. Another important feature of XRS is that it allows for other than dipole transitions to be studied, thanks to an practically unlimited range of momentum transfer offered by hard x-rays. These higher order multipole excitations can yield novel information on the electronic structure, not accessible by many other spectroscopies [2]. The availability of XRS instruments at third-generation synchrotron radiation sources has made highly accurate XRS measurements possible. XRS can be even used as a contrast mechanism in three-dimensional X-ray imaging [3]. In this contribution, the capabilities of XRS and recent examples of novel studies allowed by it will be reviewed.
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Sarkar, Shilpa, Indranil Chattopadhyay i Philippe Laurent. "Two-temperature solutions and emergent spectra from relativistic accretion discs around black holes". Astronomy & Astrophysics 642 (październik 2020): A209. http://dx.doi.org/10.1051/0004-6361/202037520.
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Aims. We investigate a two-temperature advective transonic accretion disc around a black hole and analyse its spectrum in the presence of radiative processes such as bremsstrahlung, synchrotron, and inverse-Comptonisation. The aim is to link the emergent spectra with constants of motion of the accretion disc fluid, however, the number of unknowns in two-temperature theory exceeds the number of equations for a given set of constants of motion. We intend to remove the degeneracy using a general methodology and obtain a unique solution, along with its spectrum. Methods. We used hydrodynamic equations (continuity, momentum, and energy conservation equation) to obtain sonic points and solutions. To solve these equations of motion we used the 4th order Runge-Kutta method. For the spectral analysis, general and special relativistic effects were taken into consideration. The system is, nonetheless, degenerate and we remove the degeneracy by choosing the solution with maximum entropy, as dictated by the second law of thermodynamics. Results. We obtained a unique transonic solution for a given set of constants of motion. The entropy expression is a tool used to make a selection between the degenerate solutions. We found that Coulomb coupling is a weak energy exchange term, which allows protons and electrons to settle down into two different temperatures, justifying, hence, our study of two-temperature flows. The information of the electron flow allows us to model the spectra. We show that the spectra of accretion solutions depend on the associated constants of motion. At low accretion rates, bremsstrahlung is important. A fraction of the bremsstrahlung photons may be of higher energy than the neighbouring electrons, energising them through the process of Compton scattering. Synchrotron emission, on the other hand, provides soft photons, which can be inverse-Comptonised to produce a hard power law part in the spectrum. Luminosity increases with the increase in the accretion rate of the system, as well as with the increase in BH mass. However, the radiative efficiency of the flow has almost no dependence on the BH mass, but it sharply rises with the increase in the accretion rate. The spectral index, however, hardens with the increase in the accretion rate, while it does not change much with the variation in BH mass. In addition to the constants of motion, the value of the plasma beta parameter and magnitude of magnetic dissipation in the system also helps in shaping the spectrum. A shocked solution exists in two-temperature accretion flows in a limited region of the parameter space. We find that a shocked solution is always brighter than a solution without a shock. Conclusions. An accreting system in two-temperature regime admits multiple solutions for the same set of constants of motion, producing widely different spectra. Comparing the observed spectrum with that derived from a randomly chosen accretion solution would give us a wrong estimation of the accretion parameters of the system. The form of entropy measurement we obtained helped us to remove the degeneracy of the solutions and allowed us to understand the physics of the system, shorn of arbitrary assumptions. In this work, we show how the spectra and luminosities of an accreting system depend on the constants of motion, producing solutions ranging from radiatively inefficient flows to luminous flows. An increase in BH mass quantitatively changes the system, making the system more luminous, while the spectral bandwidth also increases. A higher BH mass system spans the range from radio to gamma-rays. However, increasing the accretion rate around a BH of certain mass has little influence on the frequency range of the spectra.
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Min, Chang-Ki, Inhyuk Nam, Haeryong Yang, Gyujin Kim, Chi Hyun Shim, Jun Ho Ko, Myung-Hoon Cho i in. "Hard X-ray self-seeding commissioning at PAL-XFEL". Journal of Synchrotron Radiation 26, nr 4 (18.06.2019): 1101–9. http://dx.doi.org/10.1107/s1600577519005460.
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A wake monochromator based on a large-area diamond single crystal for hard X-ray self-seeding has been successfully installed and commissioned in the hard X-ray free-electron laser (FEL) at the Pohang Accelerator Laboratory with international collaboration. For this commissioning, the self-seeding was demonstrated with a low bunch charge (40 pC) and the nominal bunch charge (180 pC) of self-amplified spontaneous emission (SASE) operation. The FEL pulse lengths were estimated as 7 fs and 29.5 fs, respectively. In both cases, the average spectral brightness increased by more than three times compared with the SASE mode. The self-seeding experiment was demonstrated for the first time using a crystal with a thickness of 30 µm, and a narrow bandwidth of 0.22 eV (full width at half-maximum) was obtained at 8.3 keV, which confirmed the functionality of a crystal with such a small thickness. In the nominal bunch-charge self-seeding experiment, the histogram of the intensity integrated over a 1 eV bandwidth showed a well defined Gaussian profile, which is evidence of the saturated FEL and a minimal electron-energy jitter (∼1.2 × 10−4) effect. The corresponding low photon-energy jitter (∼2.4 × 10−4) of the SASE FEL pulse, which is two times lower than the Pierce parameter, enabled the seeding power to be maximized by maintaining the spectral overlap between SASE FEL gain and the monochromator.
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Suleimanov, V. F., J. Poutanen i K. Werner. "Accretion heated atmospheres of X-ray bursting neutron stars". Astronomy & Astrophysics 619 (listopad 2018): A114. http://dx.doi.org/10.1051/0004-6361/201833581.
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Some thermonuclear (type I) X-ray bursts at the neutron star surfaces in low-mass X-ray binaries take place during hard persistent states of the systems. Spectral evolution of these bursts is well described by the atmosphere model of a passively cooling neutron star when the burst luminosity is high enough. The observed spectral evolution deviates from the model predictions when the burst luminosity drops below a critical value of 20–70% of the maximum luminosity. The amplitude of the deviations and the critical luminosity correlate with the persistent luminosity, which leads us to suggest that these deviations are induced by the additional heating of the accreted particles. We present a method for computation of the neutron star atmosphere models heated by accreted particles assuming that their energy is released via Coulomb interactions with electrons. We computed the temperature structures and the emergent spectra of the atmospheres of various chemical compositions and investigate the dependence of the results on the velocity of accreted particles, their temperature and the penetration angle. We show that the heated atmosphere develops two different regions. The upper one is the hot (20–100 keV) corona-like surface layer cooled by Compton scattering, and the deeper, almost isothermal optically thick region with a temperature of a few keV. The emergent spectra correspondingly have two components: a blackbody with the temperature close to that of the isothermal region and a hard Comptonized component (a power law with an exponential decay). Their relative contribution depends on the ratio of the energy dissipation rate of the accreted particles to the intrinsic flux from the neutron star surface. These spectra deviate strongly from those of undisturbed, passively cooling neutron star atmospheres, with the main differences being the presence of a high-energy tail and a strong excess in the low-energy part of the spectrum. They also lack the iron absorption edge, which is visible in the spectra of undisturbed low-luminosity atmospheres with solar chemical composition. Using the computed spectra, we obtained the dependences of the dilution and color-correction factors as functions of relative luminosities for pure helium and solar abundance atmospheres. We show that the helium model atmosphere heated by accretion corresponding to 5% of the Eddington luminosity describes well the late stages of the X-ray bursts in 4U 1820−30.
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Sorokin, Andrey A., Yilmaz Bican, Susanne Bonfigt, Maciej Brachmanski, Markus Braune, Ulf Fini Jastrow, Alexander Gottwald, Hendrik Kaser, Mathias Richter i Kai Tiedtke. "An X-ray gas monitor for free-electron lasers". Journal of Synchrotron Radiation 26, nr 4 (12.06.2019): 1092–100. http://dx.doi.org/10.1107/s1600577519005174.
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A novel X-ray gas monitor (XGM) has been developed which allows the measurement of absolute photon pulse energy and photon beam position at all existing and upcoming free-electron lasers (FELs) over a broad spectral range covering vacuum ultraviolet (VUV), extreme ultraviolet (EUV) and soft and hard X-rays. The XGM covers a wide dynamic range from spontaneous undulator radiation to FEL radiation and provides a temporal resolution of better than 200 ns. The XGM consists of two X-ray gas-monitor detectors (XGMDs) and two huge-aperture open electron multipliers (HAMPs). The HAMP enhances the detection efficiency of the XGM for low-intensity radiation down to 105 photons per pulse and for FEL radiation in the hard X-ray spectral range, while the XGMD operates in higher-intensity regimes. The relative standard uncertainty for measurements of the absolute photon pulse energy is well below 10%, and down to 1% for measurements of relative pulse-to-pulse intensity on pulses with more than 1010 photons per pulse. The accuracy of beam-position monitoring in the vertical and horizontal directions is of the order of 10 µm.