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Gamma-ray bursts (GRBs) are the phenomena of rapid energy release of enormous power associated with the collapse or merging of stars. As a result of internal processes, populations of nonthermal accelerated particles radiating in a wide energy range are formed in them. A number of observations have shown that photons with energies up to tens of TeV are detected from some GRBs. However, due to the great energy losses of radiating particles, the explanation of this high-energy radiation in terms of standard radiation mechanisms runs into great difficulties. In this paper, based on the model of adiabatic expansion for the GRB afterglow phase, we investigate the influence of magnetic inhomogeneities on the spectra within the electron and proton synchrotron radiation mechanism by taking into account the Compton scattering of synchrotron photons. We show that the magnetic inhomogeneity effect can increase the maximum energies of the synchrotron radiation from electrons and protons several fold without affecting the maximum energies of the Compton photons being produced in the Klein–Nishina regime. [ABSTRACT FROM AUTHOR]

The features of estimating the energies of the magnetic field and relativistic electrons of synchrotron radio sources, the X-ray emission of which is produced by the invers Compton scattering of synchrotron photons (the synchrotron self-Compton process), are considered. Estimates of these physical parameters depend on the angular dimensions of the radiation sources. The effect of angular dimensions on the estimates of physical parameters is illustrated by an estimate of the magnetic induction of the hot spot A of the radio galaxy Cygnus A. We showed why it is impossible to use apparent angular dimensions of non-uniform radio sources for estimating their physical parameters. To obtain correct estimates of the energies of the field and particles, we need to use the angular size from the spherical model of the source under study, the spectrum of which coincides with the radio spectrum of the object under study. Taking such an angular size of the source, we obtain the same estimates of the physical parameters of this object, both from radio and X-ray observations. [ABSTRACT FROM AUTHOR]

Repeated Compton scattering of photons with thermal electrons is one of the fundamental processes at work in many astrophysical plasma. Solving the exact evolution equations is hard and one common simplification is based on Fokker–Planck (FP) approximations of the Compton collision term. Here we carry out a detailed numerical comparison of several FP approaches with the exact scattering kernel solution for a range of test problems assuming isotropic media and thermal electrons at various temperatures. The Kompaneets equation, being one of the most widely used FP approximations, fails to account for Klein–Nishina corrections and enhanced Doppler boosts and recoil at high energies. These can be accounted for with an alternative FP approach based on the exact first and second moments of the scattering kernel. As demonstrated here, the latter approach works very well in dilute media, but inherently fails to reproduce the correct equilibrium solution in the limit of many scattering. Conditions for the applicability of the FP approximations are clarified, overall showing that the Kompaneets equation provides the most robust approximation to the full problem, even if inaccurate in many cases. We close our numerical analysis by briefly illustrating the solutions for the spectral distortions of the cosmic microwave background (CMB) after photon injection at redshift z  ≲ 105, when double Compton and Bremsstrahlung emission can be omitted. We demonstrate that the exact treatment using the scattering kernel computed with cspack is often needed. This work should provide an important step towards accurate computations of the CMB spectral distortions from high-energy particle cascades. [ABSTRACT FROM AUTHOR]

A feasible implementation of a novel X‐ray detector for highly energetic X‐ray photons with a large solid angle coverage, optimal for the detection of Compton X‐ray scattered photons, is described. The device consists of a 20 cm‐thick sensitive volume filled with xenon at atmospheric pressure. When the Compton‐scattered photons interact with the xenon, the released photoelectrons create clouds of secondary ionization, which are imaged using the electroluminescence produced in a custom‐made multi‐hole acrylic structure. Photon‐by‐photon counting can be achieved by processing the resulting image, taken in a continuous readout mode. Based on Geant4 simulations, by considering a realistic detector design and response, it is shown that photon rates up to at least 1011 photons s−1 on‐sample (5 µm water‐equivalent cell) can be processed, limited by the spatial diffusion of the photoelectrons in the gas. Illustratively, if making use of the Rose criterion and assuming the dose partitioning theorem, it is shown how such a detector would allow obtaining 3D images of 5 µm‐size unstained cells in their native environment in about 24 h, with a resolution of 36 nm. [ABSTRACT FROM AUTHOR]

Almost 10 yr of γ-ray observations with the Fermi Large Area Telescope have revealed extreme γ-ray outbursts from flat spectrum radio quasars (FSRQs), temporarily making these objects the brightest γ-ray emitters in the sky. Yet, the location and mechanisms of the γ-ray emission remain elusive. We characterize long-term γ-ray variability and the brightest γ-ray flares of six FSRQs. Consecutively zooming in on the brightest flares, which we identify in an objective way through Bayesian blocks and a hill-climbing algorithm, we find variability on subhour timescales and as short as minutes for two sources in our sample (3C 279 and CTA 102) and weak evidence for variability at timescales less than the Fermi satellite's orbit of 95 minutes for PKS 1510–089 and 3C 454.3. This suggests extremely compact emission regions in the jet. We do not find any signs of γ-ray absorption in the broad-line region (BLR), which indicates that γ-rays are produced at distances greater than hundreds of gravitational radii from the central black hole. This is further supported by a cross-correlation analysis between γ-ray and radio/millimeter light curves, which is consistent with γ-ray production at the same location as the millimeter core for 3C 273, CTA 102, and 3C 454.3. The inferred locations of the γ-ray production zones are still consistent with the observed decay times of the brightest flares if the decay is caused by external Compton scattering with BLR photons. However, the minute-scale variability is challenging to explain in such scenarios. [ABSTRACT FROM AUTHOR]

This study suggests an improved X-ray inspection method to determine the effective atomic number to identify explosives during luggage inspection with high resolution of the effective atomic number (Z eff). To obtain high resolution in Z eff , the suggested inspection method uses the ratio of the total and Compton scattering attenuation coefficients between two different energies for decomposing the attenuation coefficients of the Rayleigh scattering and photoelectric absorption that are highly dependent on the atomic number. To acquire the total and Compton scattering coefficient ratio of two different energies, dual-energy X-ray beams and four detectors for the photons transmitted and scattered in three different angles were introduced. MCNP6 simulations were carried out for several materials with X-ray source spectra from a tungsten anode generator to show the effectiveness of the method. The estimated Z eff values with the line beam assumption showed good agreement with the reference values for explosive substances within a relative error of 3% while the additional simulation considering beam width showed increased errors that are acceptable for beam widths less than 1.5 mm. • An improved method for determining effective atomic numbers of explosives is suggested. • The separation of the photoelectric and Rayleigh components led to improved accuracy. • High accuracy of new method for explosives was shown from Monte Carlo simulations. [ABSTRACT FROM AUTHOR]

We present the momentum distributions of the nucleus and of the electrons from double ionization of the helium atom by Compton scattering of photons with hν=40 keV. We find that the doubly charged ion momentum distribution is very close to the Compton profile of the nucleus in the ground state of the helium atom, and the momentum distribution of the singly charged ion to give a precise image of the electron Compton profile. To reproduce these results, nonrelativistic calculations require the use of highly correlated initial- and final-state wave functions. [ABSTRACT FROM AUTHOR]