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We study dynamics of relativistic coronal mass ejections (CMEs), from launching by shearing of foot-points (either slowly – the 'Solar flare' paradigm, or suddenly – the 'star quake' paradigm), to propagation in the preceding magnetar wind. For slow shear, most of the energy injected into the CME is first spent on the work done on breaking through the overlaying magnetic field. At later stages, sufficiently powerful CMEs may lead to the 'detonation' of a CME and opening of the magnetosphere beyond some equipartition radius r eq, where the decreasing energy of the CME becomes larger than the decreasing external magnetospheric energy. Post-CME magnetosphere relaxes via the formation of a plasmoid-mediated current sheet, initially at ∼ r eq, and slowly reaching the light cylinder. Both the location of the foot-point shear and the global magnetospheric configuration affect the frequent/weak versus rare/powerful CME dichotomy – to produce powerful flares, the slow shear should be limited to field lines that close in near the star. After the creation of a topologically disconnected flux tube, the tube quickly (at ∼ the light cylinder) comes into force-balance with the preceding wind and is passively advected/frozen in the wind afterward. For fast shear (a local rotational glitch), the resulting large amplitude Alfvén waves lead to the opening of the magnetosphere (which later recovers similarly to the slow shear case). At distances much larger than the light cylinder, the resulting shear Alfvén waves propagate through the wind non-dissipatively. [ABSTRACT FROM AUTHOR]

Long-term periodicity in the rate of flares is observed for two repeating sources of fast radio bursts (FRBs). In this paper, we present a hydrodynamical modelling of a massive binary consisting of a magnetar and an early-type star. We model the interaction of the pulsar wind from the magnetar with an intense stellar wind. It is shown that only during a fraction of the orbital period, radio emission can escape the system. This explains the duty cycle of the two repeating FRB sources with periodic activity. The width of the transparency window depends on the eccentricity, stellar wind properties, and the viewing angle. To describe the properties of the known sources, it is necessary to assume large eccentricities ≳0.5. We apply the maser cyclotron mechanism of the radio emission generation to model spectral properties of the sources. The produced spectrum is not wide: Δν/ν ∼ 0.2 and the typical frequency depends on the radius of the shock where the emission is generated. The shock radius changes along the orbit. This, together with changing parameters of the medium, allows us to explain the frequency drift during the phase of visibility. Frequency dependence of the degree of polarization at few GHz can be a consequence of a small-scale turbulence in the shocked stellar wind. It is much more difficult to explain huge (∼105 rad/m2) and variable value of the rotation measure observed for FRB 121102. We suggest that this can be explained if the supernova explosion, which produced the magnetar happened near a dense interstellar cloud with n ∼ 100 cm−3. [ABSTRACT FROM AUTHOR]

Many explosive astrophysical events, like magnetars’ bursts and flares, are magnetically driven. We consider dynamics of such magnetic explosionsâ€"relativistic expansion of highly magnetized and highly magnetically overpressurized clouds. The corresponding dynamics are qualitatively different from fluid explosions due to the topological constraint of the conservation of the magnetic flux. Using analytical, relativistic MHD as well as force-free calculations, we find that the creation of a relativistically expanding, causally disconnected flow obeys a threshold condition: it requires sufficiently high initial overpressure and a sufficiently quick decrease of the pressure in the external medium (the preexplosion wind). In the subcritical case the magnetic cloud just “puffs up” and quietly expands with the preflare wind. We also find a compact analytical solution to Prendergast’s problemâ€"expansion of force-free plasma into a vacuum. [ABSTRACT FROM AUTHOR]

High-mass microquasar jets, produced in an accreting compact object in orbit around a massive star, must cross a region filled with stellar wind. The combined effects of the wind and orbital motion can strongly affect the jet properties on binary scales and beyond. The study of such effects can shed light on how high-mass microquasar jets propagate and terminate in the interstellar medium. We study for the first time, using relativistic hydrodynamical simulations, the combined impact of the stellar wind and orbital motion on the properties of high-mass microquasar jets on binary scales and beyond. We have performed 3-dimensional relativistic hydrodynamic simulations, using the PLUTO code, of a microquasar scenario in which a strong weakly relativistic wind from a star interacts with a relativistic jet under the effect of the binary orbital motion. The parameters of the orbit are chosen such that the results can provide insight on the jet-wind interaction in compact systems like for instance Cyg X-1 or Cyg X-3. The wind and jet momentum rates are set to values that may be realistic for these sources and lead to moderate jet bending, which together with the close orbit and jet instabilities could trigger significant jet precession and disruption. For high-mass microquasars with orbit size a ∼ 0.1 AU, and (relativistic) jet power |$L_j\sim 10^{37}(\dot{M}_w/10^{-6}\, {\rm M}_\odot \, {\rm yr}^{-1})$|  erg s−1, where |$\dot{M}_w$| is the stellar wind mass rate, the combined effects of the stellar wind and orbital motion can induce relativistic jet disruption on scales ∼1 AU. [ABSTRACT FROM AUTHOR]

We consider a magnetar flare model for fast radio bursts (FRBs). We show that millisecond bursts of sufficient power can be generated by synchrotron maser emission ignited at the reverse shock propagating through the weakly magnetized material that forms the magnetar flare. If the maser emission is generated in an anisotropic regime (due to the geometry of the production region or presence of an intense external source of stimulating photons), the duration of the maser flashes is similar to the magnetar flare duration even if the shock front radius is large. Our scenario allows for relaxing the requirements for several key parameters: the magnetic field strength at the production site, luminosity of the flare, and the production site bulk Lorentz factor. To check the feasibility of this model, we study the statistical relation between powerful magnetar flares and the rate of FRBs. The expected ratio is derived by convoluting the redshift-dependent magnetar density with its flare luminosity function above the energy limit determined by the FRB detection threshold. We obtain that only a small fraction, ∼10âˆ'5, of powerful magnetar flares trigger FRBs. This ratio agrees surprisingly well with our estimates: we obtained that 10% of magnetars should be in the evolutionary phase suitable for the production of FRBs, and only 10âˆ'4 of all flares are expected to be weakly magnetized, which is a necessary condition for the high-frequency maser emission. [ABSTRACT FROM AUTHOR]

We present a brief history and the current status of research on gamma-ray bursts (GRBs), including observations at various GRB phases: the prompt emission, afterglow, supernova/kilonova, and the host galaxy. An overview of the known phenomenological features and theoretical models for GRBs is given. Problems, the solution of which is necessary for a successful study of the phenomenon of GRB, are discussed. [ABSTRACT FROM AUTHOR]

We have developed a model of early X-ray afterglows of gamma-ray bursts originating from the reverse shock (RS) propagating through ultrarelativistic, highly magnetized pulsar-like winds produced by long-lasting central engines. We first performed fluid and magnetohydrodynamic numerical simulations of relativistic double explosions. We demonstrate that even for constant properties of the wind a variety of temporal behaviors can be produced, depending on the energy of the initial explosion and the wind power, the delay time for the switch-on of the wind, and the magnetization of the wind. X-ray emission of the highly magnetized RS occurs in the fast-cooling regime—this ensures high radiative efficiency and allows fast intensity variations. We demonstrate that (i) RS emission naturally produces light curves, showing power-law temporal evolution with various temporal indices; (ii) mild wind power, of the order of ∼1046 erg s−1 (equivalent isotropic), can reproduce the afterglows' plateau phase; (iii) termination of the wind can produce sudden steep decays; and (iv) short-duration afterglow flares are due to mild variations in the wind luminosity, with small total injected energy. [ABSTRACT FROM AUTHOR]

Pulsars moving through interstellar medium (ISM) produce bow shocks detected in hydrogen H α line emission. The morphology of the bow shock nebulae allows one to probe the properties of ISM on scales ∼0.01 pc and smaller. We performed 2D relativistic magnetohydrodynamic modelling of the pulsar bow shock and simulated the corresponding H α emission morphology. We find that even a mild spatial inhomogeneity of ISM density, δρ/ρ ∼ 1, leads to significant variations of the shape of the shock seen in H α line emission. We successfully reproduce the morphology of the Guitar Nebula. We infer quasi-periodic density variations in the warm component of ISM with characteristic length of ∼0.1 pc. Structures of this scale might be also responsible for the formation of the fine features seen at the forward shock of Tycho supernova remnant (SNR) in X-rays. Formation of such short periodic density structures in the warm component of ISM is puzzling, and bow-shock nebulae provide unique probes to study this phenomenon. [ABSTRACT FROM AUTHOR]

The relevance of the study and its scientific novelty lies in the development of the original idea that the methodological potential of social entrepreneurship, as a tool for studying processes and changes in the social sphere, should be in demand when substantiating the model of legal support for Russian environmental entrepreneurship, the development of which is recognized as the most important factor for sustainable development regions, contributing to the transition to a rational model of environmental management and increase its competitiveness. The purpose of the study is to assess the prospects for the implementation of the simulated theoretical design of the legal support of social and environmental entrepreneurship, as the final stage of the study. Research methods: empirical (comparative legal, description, interpretation); theoretical (formal and dialectical logic.) Research results: 1). The study showed that in world practice the development of legislation on environmental entrepreneurship occurs in unified connection with legislation on social entrepreneurship. However, the Russian socio-entrepreneurial legal model does not correspond to global trends, is not able to become an impetus and the basis for the development of environmental entrepreneurship and needs to be adjusted. 2). A fundamentally new conceptual solution to the conflict was substantiated by adopting a special federal law based on successful foreign experience containing state guarantees for the development of social and environmental entrepreneurship, not limited solely to state support. Given the relationship of social and environmental entrepreneurship, it is proposed to adjust the application of the term by proposing a more specific one - "socio-environmental entrepreneurship", and therefore the bill should be called "On state guarantees for the development of socioenvironmental entrepreneurship". 3). The key idea of the concept of the bill is that the goal of social and environmental business is not profit, but a positive social and environmental impact on society and the environment, where profit is considered as a means of realizing the mission of a social and environmental enterprise aimed at solving social and environmental issues. The practical significance lies in the fact that the constructed legal model will be most in demand in the development of competition in regional markets and the solution of major social problems: eradicating poverty and protecting the environment. [ABSTRACT FROM AUTHOR]

We suggest that narrow, long radio filaments near the Galactic Centre arise as kinetic jets – streams of high-energy particles escaping from ram pressure confined pulsar wind nebulae (PWNe). The reconnection between the PWN and interstellar magnetic field allows pulsar wind particles to escape, creating long narrow features. They are the low-frequency analogues of kinetic jets seen around some fast-moving pulsars, such as The Guitar and The Lighthouse PWNe. The radio filaments trace a population of pulsars also responsible for the Fermi GeV excess produced by the Inverse Compton scattering by the pulsar wind particles. The magnetic flux tubes are stretched radially by the large-scale Galactic winds. In addition to PWNe accelerated particles can be injected at supernovae remnants. The model predicts variations of the structure of the largest filaments on scales of ∼dozens of years – smaller variations can occur on shorter time-scales. We also encourage targeted observations of the brightest sections of the filaments and of the related unresolved point sources in search of the powering PWNe and pulsars. [ABSTRACT FROM AUTHOR]

Some fast-moving pulsars, such as the Guitar and the Lighthouse, exhibit asymmetric non-thermal emission features that extend well beyond their ram pressure confined pulsar wind nebulae (PWNe). Based on our 3D relativistic simulations, we analytically explain these features as kinetically streaming pulsar wind particles that escaped into the interstellar medium (ISM) due to reconnection between the PWN and ISM magnetic fields. The structure of the reconnecting magnetic fields at the incoming and outgoing regions produces highly asymmetric magnetic bottles therefore and result in asymmetric extended features. For the features to become visible, the ISM magnetic field should be sufficiently high, B ISM > 10  |$\mu$| G. We also discuss archival observations of PWNe displaying evidence of kinetic jets: the Dragonfly PWN (PSR J2021 + 3651), G327.1–1.1, and MSH 11–62, the latter two of which exhibit symmetric 'snail eyes' morphologies. We suggest that in those cases the pulsar is moving along the ambient magnetic field in a frisbee-type configuration. [ABSTRACT FROM AUTHOR]

Bow-shock pulsar wind nebulae (PWNe) show a variety of morphological shapes. We attribute this diversity to the geometrical factors: relative orientations of the pulsar rotation axis, proper velocity, and the line of sight (magnetic inclination angle may also have certain influence on the morphology). We identify three basic types of bow-shock nebulae: (i) a rifle bullet (pulsar spin axis and proper velocity are aligned), (ii) a 'Frisbee' (pulsar spin axis and proper velocity are orthogonal with the spin axis lying in the plane of the sky), and (iii) a 'Cart wheel' (such as frisbee but the spin axis is perpendicular to the plane of the sky). Using results of the 3D magnetohydrodynamics simulations, as well as analytical calculations, we reproduce the key morphological features of the bow-shock PWNe, as well as variations seen across different systems. Magnetic stresses within the shocked pulsar wind affect the overall structure strongly, producing 'whiskers', 'tails', 'filled-in', and 'mushroom' shapes, as well as non-symmetric morphologies. On the other hand, the interstellar medium inhomogeneities and the anisotropy of the energy flux in the pulsar wind have only a mild impact of the PWN morphology. In a few cases, when we clearly identify specific morphological structures, our results do not favour alignment of the pulsar spin axis and proper velocity. Our calculations of the underlying emission processes explain the low-synchrotron X-ray efficiency (in terms of the spin-down luminosity) and imply an energetically subdominant contribution of the inverse Compton process. [ABSTRACT FROM AUTHOR]

In the standard synchrotron afterglow model, a power law of electrons is responsible for all aspects of photon production and absorption. Recent numerical work has shown that the vast majority of particles in the downstream medium are actually 'thermal' particles, which were shock heated but did not enter the Fermi acceleration process (the name stands in contrast to the non-thermal high-energy tail, rather than connoting a Maxwellian distribution). There are substantial differences at optical and higher energies when these thermal electrons participate in the afterglow, but early work along these lines ignored the radio end of the electromagnetic spectrum. We report here on an extension of previous Monte Carlo simulations of gamma-ray burst afterglows. The model now includes the synchrotron self-absorption (SSA) process and so can simulate afterglows across the entire EM spectrum, and several orders of magnitude in time. In keeping with earlier work, inclusion of the thermal electrons increases the SSA frequency by a factor of 30, and the radio intensity by a factor of 100. Furthermore, these changes happen with no modification to the late optical or X-ray afterglow. Our results provide very strong evidence that thermal electrons must be considered in any multiwavelength model for afterglows. [ABSTRACT FROM AUTHOR]

HESS J0632+057 is an eccentric gamma-ray Be binary that produces non-thermal radio, Xrays, GeV and very high-energy gamma-rays. The non-thermal emission of HESS J0632+057 is modulated with the orbital period, with a dominant maximum before apastron passage. The nature of the compact object in HESS J0632+057 is not known, although it has been proposed to be a young pulsar as in PSR B1259–63, the only gamma-ray emitting high-mass binary known to host a non-accreting pulsar. In this letter, we present hydrodynamical simulations of HESS J0632+057 in the context of a pulsar and a stellar wind interacting in an eccentric binary, and propose a scenario for the non-thermal phenomenology of the source. In this scenario, the non-thermal activity before and around apastron is linked to the accumulation of non-thermal particles in the vicinity of the binary, and the sudden drop of the emission before apastron is produced by the disruption of the two-wind interaction structure, allowing these particles to escape efficiently. In addition to providing a framework to explain the nonthermal phenomenology of the source, this scenario predicts extended, moving X-ray emitting structures similar to those observed in PSR B1259-63. [ABSTRACT FROM AUTHOR]

The stability of current sheets in collisionless relativistic pair plasma was studied via twodimensional two-fluid relativistic magnetohydrodynamic simulations with vanishing internal friction between fluids. In particular, we investigated the linear growth of the tearing and drift-kink modes in the current sheets both with and without the guide field and obtained the growth rates which are very similar to what has been found in the corresponding particle in cell (PIC) simulations. This suggests that the two-fluid simulations can be useful in studying the large-scale dynamics of astrophysical relativistic plasmas in problems involving magnetic reconnection. [ABSTRACT FROM AUTHOR]

Context. The structure formed by the shocked winds of a massive star and a non-accreting pulsar in a binary system suffers periodic and random variations of orbital and non-linear dynamical origins. The characterization of the evolution of the wind interaction region is necessary for understanding the rich phenomenology of these sources. Aims. For the first time, we simulate in 3 dimensions the interaction of isotropic stellar and relativistic pulsar winds along one full orbit, on scales well beyond the binary size. We also investigate the impact of grid resolution and size, and of different state equations: a γ -constant ideal gas, and an ideal gas with γ dependent on temperature. Methods. We used the code PLUTO to carry out relativistic hydrodynamical simulations in 2 and 3 dimensions of the interaction between a slow dense wind and a mildly relativistic wind with Lorentz factor 2, along one full orbit in a region up to ∼100 times the binary size. The di erent 2-dimensional simulations were carried out with equal and larger grid resolution and size, and one was done with a more realistic equation of state than in 3 dimensions. Results. The simulations in 3 dimensions confirm previous results in 2 dimensions, showing: a strong shock induced by Coriolis forces that terminates the pulsar wind also in the opposite direction to the star; strong bending of the shocked-wind structure against the pulsar motion; and the generation of turbulence. The shocked flows are also subject to a faster development of instabilities in 3 dimensions, which enhances shocks, two-wind mixing, and large-scale disruption of the shocked structure. In 2 dimensions, higher resolution simulations confirm lower resolution results, simulations with larger grid sizes strengthen the case for the loss of the general coherence of the shocked structure, and simulations with two di erent equations of state yield very similar results. In addition to the Kelvin-Helmholtz instability, discussed in the past, we find that the Richtmyer-Meshkov and the Rayleigh-Taylor instabilities are very likely acting together in the shocked flow evolution. Conclusions. Simulations in 3 dimensions confirm that the interaction of stellar and pulsar winds yields structures that evolve nonlinearly and become strongly entangled. The evolution is accompanied by strong kinetic energy dissipation, rapid changes in flow orientation and speed, and turbulent motion. The results of this work strengthen the case for the loss of the coherence of the whole shocked structure on large scales, although simulations of more realistic pulsar wind speeds are needed. [ABSTRACT FROM AUTHOR]

Context. The Fermi bubbles are part of a complex region of the Milky Way. This region presents broadband extended non-thermal radiation, apparently coming from a physical structure rooted at the Galactic centre and with a partly ordered magnetic field threading it. Aims. We explore the possibility of an explosive origin for the Fermi bubble region to explain its morphology, in particular that of the large-scale magnetic fields, and provide context for the broadband non-thermal radiation. Methods. We performed 3D magnetohydrodynamical simulations of an explosion that occurred a few million years ago that pushed and sheared a surrounding magnetic loop, anchored in the molecular torus around the Galactic centre. Results. Our results can explain the formation of the large-scale magnetic structure in the Fermi bubble region. Consecutive explosive events may match the morphology of the region better. Faster velocities at the top of the shocks than at their sides may explain the hardening with distance from the Galactic plane found in the GeV emission. Conclusions. In the framework of our scenario, we estimate the lifetime of the Fermi bubbles as ≈2 × 106 yr, with a total energy injected in the explosion(s) of ≳1055 ergs. The broadband non-thermal radiation from the region may be explained by leptonic emission, which is more extended in radio and X-rays, and is confined to the Fermi bubbles in gamma rays. [ABSTRACT FROM AUTHOR]

We propose a model to explain the ultra-bright GeV gamma-ray flares observed from the blazar 3C454.3. The model is based on the concept of a relativistic jet interacting with compact gas condensations produced when a star (a red giant) crosses the jet close to the central black hole. The study includes an analytical treatment of the evolution of the envelope lost by the star within the jet, and calculations of the related high-energy radiation. The model readily explains the day-long that varies on timescales of hours, GeV gamma-ray flare from 3C454.3, observed during 2010 November on top of a plateau lasting weeks. In the proposed scenario, the plateau state is caused by a strong wind generated by the heating of the stellar atmosphere due to nonthermal particles accelerated at the jet-star interaction region. The flare itself could be produced by a few clouds of matter lost by the red giant after the initial impact of the jet. In the framework of the proposed scenario, the observations constrain the key model parameters of the source, including the mass of the central black hole: MBH 109M☉, the total jet power: Lj≃1048 erg s-1, and the Doppler factor of the gamma-ray emitting clouds: δ≃20. Whereas we do not specify the particle acceleration mechanisms, the potential gamma-ray production processes are discussed and compared in the context of the proposed model.We argue that synchrotron radiation of protons has certain advantages compared to other radiation channels of directlyaccelerated electrons. An injected proton distribution α E -1 or harder below the relevant energies would be favored to alleviate the tight energetic constraints and to avoid the violation of the observational low-energy constraints. [ABSTRACT FROM AUTHOR]

ABSTRACT Isolated black holes (IBHs) are not usually considered to be important astrophysical sources, since, even in the case of a high accretion rate, an accretion disc rarely can be formed due to the small angular momentum of the infalling matter. Thus, such systems are not expected to feature thermal disc emission which makes the dominant contribution to the radiative output of binary systems harbouring a BH. Moreover, due to their relatively modest accretion rates, these objects are not conventionally treated as feasible jet sources. However, the large number of IBHs in the Galaxy, estimated to be ∼108, implies a very high density of 10−4 pc−3 and an average distance between IBHs of ∼10 pc. Our study shows that the magnetic flux, accumulated on the horizon of an IBH because of accretion of interstellar matter, allows the Blandford-Znajeck mechanism to be activated. Thus, electron-positron jets can be launched. We have performed 2D numerical modelling which allowed the jet power to be estimated. Their inferred properties make such jets a feasible electron accelerator which, in molecular clouds (MCs), allows electron energy to be boosted up to ∼1 PeV. For the conditions expected in MCs, the radiative cooling time should be comparable to the escape time. Thus, these sources can contribute both to the population of unidentified point-like sources and to the local cosmic-ray (CR) electron spectrum. The impact of the generated electron CRs depends on the diffusion rate inside MCs. If the diffusion regime in a MC is similar to Galactic diffusion, the produced electrons should rapidly escape the cloud and contribute to the Galactic CR population at very high energies, >100 TeV. However, due to the modest jet luminosity (at the level of ∼1035 erg s−1) and low filling factor of MCs, these sources cannot make a significant contribution to the spectrum of CR electrons at lower energies. On the other hand, if the diffusion within MCs operates at a rate close to the Bohm limit, the CR electrons escaping from the source should be confined in the cloud, significantly contributing to the local density of CRs. The inverse Compton emission of these locally generated CRs may explain the variety of gamma-ray spectra detected from nearby MCs. [ABSTRACT FROM AUTHOR]

Context. The winds from a non-accreting pulsar and a massive star in a binary system collide forming a bow-shaped shock structure. The Coriolis force induced by orbital motion deflects the shocked flows, strongly affecting their dynamics. Aims. We study the evolution of the shocked stellar and pulsar winds on scales in which the orbital motion is important. Potential sites of non-thermal activity are investigated. Methods. Relativistic hydrodynamical simulations in two dimensions, performed with the code PLUTO and using the adaptive mesh refinement technique, are used to model interacting stellar and pulsar winds on scales ∼80 times the distance between the stars. The hydrodynamical results suggest the suitable locations of sites for particle acceleration and non-thermal emission. Results. In addition to the shock formed towards the star, the shocked and unshocked components of the pulsar wind flowing away from the star terminate by means of additional strong shocks produced by the orbital motion. Strong instabilities lead to the development of turbulence and an effective two-wind mixing in both the leading and trailing sides of the interaction structure, which starts to merge with itself after one orbit. The adopted moderate pulsar-wind Lorentz factor already provides a good qualitative description of the phenomena involved in high-mass binaries with pulsars, and can capture important physical effects that would not appear in non-relativistic treatments. Conclusions. Simulations show that shocks, instabilities, and mass-loading yield efficient mass, momentum, and energy exchanges between the pulsar and the stellar winds. This renders a rapid increase in the entropy of the shocked structure, which will likely be disrupted on scales beyond the simulated ones. Several sites of particle acceleration and low- and high-energy emission can be identified. Doppler boosting will have significant and complex effects on radiation. [ABSTRACT FROM AUTHOR]

We propose a new model for the description of ultra-short flares from TeV blazars by compact magnetized condensations (blobs), produced when red giant stars cross the jet close to the central black hole. Our study includes a simple dynamic model for the evolution of the envelope lost by the star in the jet and its high-energy nonthermal emission through different leptonic and hadronic radiation mechanisms. We show that the fragmented envelope of the star can be accelerated to Lorentz factors up to 100 and effectively radiate the available energy in gamma rays predominantly through proton synchrotron radiation or external inverse Compton scattering of electrons. The model can readily explain the minute-scale TeV flares on top of longer (typical timescales of days) gamma-ray variability as observed from the blazar PKS 2155-304. In the framework of the proposed scenario, the key parameters of the source are robustly constrained. In the case of proton synchrotron origin of the emission, a mass of the central black hole of MBH 108 M⊙, a total jet power of Lj ≈ 2 x 1047 erg s-1, and a Doppler factor of the gamma-ray emitting blobs of δ ≥ 40 are required. For the external inverse Compton model, parameters of MBH ≈ 108 M⊙, Lj ≈ 1046 erg s-1, and δ ≥ 150 are required. [ABSTRACT FROM AUTHOR]

ABSTRACT In this paper, we study the wind accretion on to a rotating black hole in a close binary system that harbours a young massive star. It is shown that the angular momentum of the accreted stellar wind material is not sufficient for the formation of an accretion disc. However, in the conditions considered, the Blanford-Znajek mechanism can be activated, and thus powerful jets can be launched in the direction of the rotation axis of the black hole. Importantly, no observational signatures of accretion, as are typically seen from the thermal X-ray emission of accretion discs, are expected in the suggested scenario. Here, the properties of the generated jet are studied numerically in the framework of a two-dimensional general relativity magnetohydrodynamical approach. Because of the accumulation of the magnetic flux at the black hole horizon, the jet power is expected to be modulated on a subsecond time-scale. Although the intervals between the jet active phases depend on the magnetic flux that escapes from the black hole horizon (which can be modelled self-consistently only using a three-dimensional code), a general estimate of the averaged jet power is obtained. It is shown that for the black hole rotation, expected in a stellar binary system (the dimensionless rotation parameter a= 0.5), approximately 5 per cent of the accreted rest energy can be channelled into the jets. In the case of the faster rotation of the black hole, the efficiency is expected to be significantly higher (e.g. for the dimensionless rotation parameter a= 0.95, the jet carries approximately 20 per cent of the accreted rest energy). In the specific case of the gamma-ray binary system LS 5039, the obtained jet luminosity can be responsible for the observed GeV radiation if Doppler boosting is invoked, which can enhance the apparent flux from the system. [ABSTRACT FROM AUTHOR]

ABSTRACT The existence of extended emission (EE) is an intriguing property of short-duration gamma-ray bursts, because the nature of the EE is still unclear. It might be a rising X-ray afterglow, or it could be a manifestation of the prolonged activity of a central engine. We consider short-duration gamma-ray bursts, emphasizing the common properties of both short bursts and short bursts with EE. Assuming that the EE with broad dynamic range is a common property of short bursts, we propose a two jet model which can describe both short main episode of hard spectra emission, specific for short bursts, and softer spectra EE by different off axis position of observer. The model involves a short-duration jet, which is powered by heating due to annihilation, and a long-lived Blandford-Znajek jet with a significantly narrow opening angle. Our proposed model is a plausible mechanism for short-duration burst energization. It can explain short bursts both with and without EE within a single class of progenitor. [ABSTRACT FROM AUTHOR]

BSTRACT [ABSTRACT FROM AUTHOR]

The prospects for using wastes from cellulose-containing feedstock for manufacturing a broad spectrum of motor fuel components (biodiesel, bioethanol, biogasoline) are examined. The possibility of biosynthesis of lipids similar in composition and properties to soy oil was demonstrated on the example of fungal strains Agrocybe aegerita and Lentinus edodes. These lipids can serve as an intermediate product for synthesis of biodiesel fuel due to the high content of higher fatty acid triglycerides. The results of catalytic processing of bioethanol from a wood substrate obtained after solid-phase cultivation of fungi in a mixture of aliphatic and aromatic hydrocarbons are reported. [ABSTRACT FROM AUTHOR]

The very first stars in the Universe can be very massive, up to . If born in large numbers, such massive stars can have a strong impact on the subsequent star formation, producing strong ionizing radiation and contaminating the primordial gas with heavy elements. They would leave behind massive black holes that could act as seeds for growing supermassive black holes of active galactic nuclei. Given the anticipated fast rotation, such stars would end their life as supermassive collapsars and drive powerful magnetically dominated jets. In this Letter, we investigate the possibility of observing the bursts of high-energy emission similar to the long gamma-ray bursts associated with normal collapsars. We show that during the collapse of supercollapsars, the Blandford–Znajek mechanism can produce jets as powerful as few erg s−1 and release up to 1054 erg of the black hole rotational energy. Due to the higher intrinsic time-scale and higher redshift, the initial bright phase of the burst can last for about 104 s, whereas the central engine would remain active for about 1 d. Due to the high redshift the burst spectrum is expected to be soft, with the spectral energy distribution peaking at around 20–30 keV. The peak total flux density is relatively low, , but not prohibitive. If one supercollapsar is produced per every minihalo of dark matter arising from the 3σ cosmological fluctuations, then the whole sky frequency of such bursts could reach several tens per year. [ABSTRACT FROM AUTHOR]

The strong dependence of the neutrino annihilation mechanism on the mass accretion rate makes it difficult to explain the long-duration gamma-ray bursts (LGRBs) with duration in excess of 100 s as well as the precursors separated from the main gamma-ray pulse by few hundreds of seconds. Even more difficult is to explain the Swift observations of the shallow decay phase and X-ray flares, if they indeed indicate activity of the central engine for as long as 104 s. These data suggest that some other, most likely magnetic mechanisms have to be considered. Since the efficiency of magnetic mechanisms does not depend that much on the mass accretion rate, the magnetic models do not require the development of accretion disc within the first few seconds of the stellar collapse and hence do not require very rapidly rotating stellar cores at the pre-supernova (SN) state. This widens the range of potential LGRB progenitors. In this paper, we re-examine the close binary scenario allowing for the possibility of late development of accretion discs in the collapsar model and investigate the available range of mass accretion rates, black hole (BH) masses and spins. We find that the BH mass can be much higher than , usually assumed in the collapsar model, and normally exceeds half of the pre-SN mass. The BH spin is rather moderate, , but still high enough for the Blandford–Znajek mechanism to remain efficient provided the magnetic field is sufficiently strong. Our numerical simulations confirm the possibility of magnetically driven stellar explosions, in agreement with previous studies, but point towards the required magnetic flux on the BH horizon in excess of . At present, we cannot answer with certainty whether such a strong magnetic field can be generated in the stellar interior. Perhaps, the SN explosions associated with LGRBs are still neutrino-driven and their gamma-ray signature is the precursors. The SN blast clears up escape channels for the magnetically driven gamma-ray burst (GRB) jets, which may produce the main pulse. In this scenario, the requirements on the magnetic field strength can be lowered. A particularly interesting version of the binary progenitor involves merger of a Wolf–Rayet star with an ultracompact companion, neutron star or BH. In this case, we expect the formation of very long-lived accretion discs, that may explain the phase of shallow decay and X-ray flares observed by Swift. Similarly long-lived magnetic central engines are expected in the current single star models of LGRB progenitors due to their assumed exceptionally fast rotation. [ABSTRACT FROM AUTHOR]

The collapse of massive stars may result in the formation of accreting black holes in their interiors. The accreting stellar matter may advect substantial magnetic flux on to the black hole and promote the release of its rotational energy via magnetic stresses (the Blandford–Znajek mechanism). In this paper we explore whether this process can explain the stellar explosions and relativistic jets associated with long gamma-ray bursts. In particular, we show that the Blandford–Znajek mechanism is activated when the rest mass–energy density of matter drops below the energy density of the magnetic field in the near vicinity of the black hole (within its ergosphere). We also discuss whether such a strong magnetic field is in conflict with the rapid rotation of the stellar core required in the collapsar model, and suggest that the conflict can be avoided if the progenitor star is a component of a close binary. In this case the stellar rotation can be sustained via spin-orbital interaction. In an alternative scenario the magnetic field is generated in the accretion disc, but in this case the magnetic flux through the black hole ergosphere is not expected to be sufficiently high to explain the energetics of hypernovae by the BZ mechanism alone. However, this energy deficit can be recovered via the additional power provided by the disc. [ABSTRACT FROM AUTHOR]

Using the self-consistent-charge density-functional tight-binding (SCC-DFTB) method, we studied the effect of axial stretching on the electrical conductivity and quantum capacitance of hybrid films formed by AB-stacked bilayer graphene and horizontally oriented single-walled carbon nanotubes (SWCNTs) with indices chirality (12, 6). The paper discusses several topological models of hybrid graphene/SWCNT (12, 6) films, which differ in the width of the graphene layer in the supercell and in the value of the shift between the graphene layers. It is shown that axial stretching has a different effect on the electrical conductivity and quantum capacity of the hybrid graphene/SWCNT (12, 6) film depending on the width of the graphene layer. For a topological model with a minimum width of the graphene layer (2 hexagons) under a 10% stretching strain, the transformation of bilayer graphene from planar to wave-like structures is characteristic. This transformation is accompanied by the appearance of the effect of anisotropy of electrical conductivity and a sharp decrease in the maximum of quantum capacitance. For a topological model with a graphene layer width of 4 hexagons, axial stretching, on the contrary, leads to a decrease in the effect of anisotropy of electrical conductivity and insignificant changes in the quantum capacitance. Based on the obtained results, the prospects for using hybrid graphene/SWCNT (12, 6) films as a material for creating flexible electrodes of supercapacitors are predicted. [ABSTRACT FROM AUTHOR]

We present numerical simulations of cold, axisymmetric, magnetically driven relativistic outflows. The outflows are initially sub-Alfvénic and Poynting-flux dominated, with total–to–rest-mass energy flux ratio up to μ ~ 620. To study the magnetic acceleration of jets we simulate flows confined within a funnel with a rigid wall of prescribed shape, which we take to be z ∝ ra (in cylindrical coordinates, with a ranging from 1 to 2). This allows us to eliminate the numerical dissipative effects induced by a free boundary with an ambient medium. We find that in all cases they converge to a steady state characterized by a spatially extended acceleration region. For the jet solutions the acceleration process is very efficient — on the outermost scale of the simulation more than half of the Poynting flux has been converted into kinetic energy flux, and the terminal Lorentz factor approached its maximum possible value (Γ∞ ≃ μ). The acceleration is accompanied by the collimation of magnetic field lines in excess of that dictated by the funnel shape. The numerical solutions are generally consistent with the semi-analytic self-similar jets solutions and the spatially extended acceleration observed in some astrophysical relativistic jets. In agreement with previous studies, we also find that the acceleration is significantly less effective for wind solutions suggesting that pulsar winds may remain Poynting dominated when they reach the termination shock. [ABSTRACT FROM AUTHOR]

One of the urgent problems of materials science is the search for the optimal combination of graphene modifications and carbon nanotubes (CNTs) for the formation of layered hybrid material with specified physical properties. High electrical conductivity and stability are one of the main optimality criteria for a graphene/CNT hybrid structure. This paper presents results of a theoretical and computational study of the peculiarities of the atomic structure and the regularities of current flow in hybrid films based on single-walled carbon nanotubes (SWCNTs) with a diameter of 1.2 nm and bilayer zigzag graphene nanoribbons, where the layers are shifted relative to the other. It is found that the maximum stresses on atoms of hybrid film do not exceed ~0.46 GPa for all considered topological models. It is shown that the electrical conductivity anisotropy takes place in graphene/SWCNT hybrid films at a graphene nanoribbon width of 4 hexagons. In the direction along the extended edge of the graphene nanoribbon, the electrical resistance of graphene/SWCNT hybrid film reaches ~125 kOhm; in the direction along the nanotube axis, the electrical resistance is about 16 kOhm. The prospects for the use of graphene/SWCNT hybrid films in electronics are predicted based on the obtained results. [ABSTRACT FROM AUTHOR]

In this Letter, we briefly describe the first results of our numerical study on the possibility of magnetic origin of relativistic jets of long-duration gamma-ray bursters within the collapsar scenario. We track the collapse of massive rotating stars on to a rotating central black hole using axisymmetric general relativistic magnetohydrodynamic code that utilizes a realistic equation of state of stellar matter, and takes into account the cooling associated with emission of neutrinos and the energy losses due to dissociation of nuclei. The neutrino heating is not included. We describe the solution for one particular model where the progenitor star has magnetic field . The solution exhibits strong explosion driven by the Poynting-dominated jets whose power exceeds . The jets originate mainly from the black hole, and they are powered via the Blandford–Znajek mechanism. [ABSTRACT FROM AUTHOR]

In this paper, we report on the early evolution of a core-collapse supernova explosion following the birth of a magnetar with the dipolar magnetic field of and the rotational period of 2 ms, which was studied by means of axisymmetric general relativistic magnetohydrodynamic simulations. In this study, we use realistic equation of state and take into account the cooling and heating associated with emission, absorption, annihilation, and scattering of neutrinos; the neutrino transport is treated in the optically-thin regime. The supernova explosion is initiated via introducing into the initial solution the ‘radiation bubble’, whose total thermal energy is comparable with the typical energy of supernova ejecta. The numerical models exhibit highly collimated magnetically driven jets very early on. The jets are super-Alfvénic but remain subfast until the end of the simulations . The power released in the jets is about which implies the spin-down time of ≃37 s. The total rotational energy of the magnetar, , is sufficient to drive a hypernova but it is not clear as to how large a fraction of this energy can be transferred to the stellar ejecta. Given the observed propagation speed of the jets, , they are expected to traverse the progenitor in few seconds and after this most of the released rotational energy would be simply carried away by these jets into the surrounding space. Three-dimensional effects such as the kink mode instability may reduce the jet propagation speed and increase the amount of energy transferred by the jets to the supernova ejecta. Our results provide the first more or less self-consistent numerical model of a central engine capable of producing, in the supernova setting and on a long-term basis, collimated jets with sufficient power to explain long-duration gamma-ray bursts (GRBs) and their afterglows. Although the flow speed of our jets is relatively low, only , the cooling of protoneutron star will eventually result in much higher magnetization of its magnetosphere and ultrarelativistic asymptotic speeds of the jets. Given the relatively long cooling time-scale, we still expect the jets to be only weakly relativistic by the time of break-out. This leads to a model of GRB jets with a systematic longitudinal variation in the Lorentz factor which may have specific observational signatures both in the prompt and in the afterglow emission. The simulations also reveal quasi-periodic ejection of plasma clouds into the jet on a time-scale of 20 ms related to the large-scale global oscillation of magnetar's magnetosphere caused by the opening–closing of the dead zone field lines. These kinds of central engine variability may be partly responsible for the internal shocks of GRB jets and the short-time variability of their gamma-ray emission. [ABSTRACT FROM AUTHOR]

We present numerical simulations of axisymmetric, magnetically driven relativistic jets. Our special-relativistic, ideal-magnetohydrodynamics numerical scheme is specifically designed to optimize accuracy and resolution and to minimize numerical dissipation. In addition, we implement a grid-extension method that reduces the computation time by up to three orders of magnitude and makes it possible to follow the flow up to six decades in spatial scale. To eliminate the dissipative effects induced by a free boundary with an ambient medium we assume that the flow is confined by a rigid wall of a prescribed shape, which we take to be z∝ r a (in cylindrical coordinates, with a ranging from 1 to 3). We also prescribe, through the rotation profile at the inlet boundary, the injected poloidal current distribution: we explore cases where the return current flows either within the volume of the jet or on the outer boundary. The outflows are initially cold, sub-Alfvénic and Poynting flux-dominated, with a total-to-rest-mass energy flux ratio μ∼ 15. We find that in all cases they converge to a steady state characterized by a spatially extended acceleration region. The acceleration process is very efficient: on the outermost scale of the simulation as much as of the Poynting flux has been converted into kinetic energy flux, and the terminal Lorentz factor approaches its maximum possible value (Γ∞≃μ). We also find a high collimation efficiency: all our simulated jets (including the limiting case of an unconfined flow) develop a cylindrical core. We argue that this could be the rule for current-carrying outflows that start with a low initial Lorentz factor (Γ0∼ 1). Our conclusions on the high acceleration and collimation efficiencies are not sensitive to the particular shape of the confining boundary or to the details of the injected current distribution, and they are qualitatively consistent with the semi-analytic self-similar solutions derived by Vlahakis and Königl. We apply our results to the interpretation of relativistic jets in active galactic nuclei: we argue that they naturally account for the spatially extended accelerations inferred in these sources (Γ∞≳ 10 attained on radial scales R≳ 1017 cm) and are consistent with the transition to the matter-dominated regime occurring already at R≳ 1016 cm. [ABSTRACT FROM AUTHOR]

Bolometric light curves for the afterglow resulting from the passage of a gamma-ray burst through a molecular cloud are computed. The profile and duration of the afterglow light curve depend strongly on the distribution of matter in the cloud, the degree of collimation of the gamma-ray radiation, and the observing conditions. The peak can be reached as soon as seven days (the gamma-ray burst is located at some distance from the center of a molecular cloud with small-scale density enhancements), or as long as one to three years (the gamma-ray burst is located at the center of a uniform molecular cloud) after the burst. The bolometric luminosity of the re-radiated signal can reach 6.5×1042 erg/s.© 2005 Pleiades Publishing, Inc. [ABSTRACT FROM AUTHOR]

Observations of the afterglows of gamma ray bursts (GRBs) in different spectral ranges yield valuable information both about the nature of GRBs and about the properties of the surrounding medium. A powerful infrared (IR) afterglow has been observed at the site of the strong GRB041219. Here we interpret the observed IR afterglow as the result of a reprocessing of gamma radiation on dust in a cloud surrounding the GRB source. In this model we do not expect the appearance of a prompt optical afterglow which should be absorbed by the surrounding dust cloud. We estimate the collimation angle of the gamma radiation and obtain limits on the red shift (distance to the GRB source) by matching the model parameters to the experimental data. [ABSTRACT FROM AUTHOR]

Motion of two gravitating spherical stellar shells around a massive central body is considered. Each shell consists of point particles with the same specific angular momenta and energies. In the case when one can neglect the influence of gravitation of one (“light”) shell onto another (“heavy”) shell (“restricted problem”) the structure of the phase space is described. The scaling laws for the measure of the domain of chaotic motion and for the minimal energy of the light shell sufficient for its escape to infinity are obtained. [ABSTRACT FROM AUTHOR]

The interaction of a powerful cosmological gamma-ray burst (GRB) with a dense molecular cloud is modeled. Two-dimensional gas-dynamical flows were computed for various configurations of the cloud. In the spherically symmetrical case, the gas velocity does not exceed ∼ 2 × 10³&radicE/1.6 × 1053;km/s. If the GRB precursor has an anisotropic wind, a conical cavity can form in the nearby region of themolecular cloud. The propagation of the gamma-ray pulse in this cavity leads to the formation of a rapidly moving hot clump of matter, with the gas velocity reaching 1.8 ×104 km/s for gammaray energy of E = 1.6×1053 erg. In all the computations, the velocity of the moving material ismuch lower than the velocity of light, the volume of gas affected by the motion is small, and the influence of the gas motions on the light curve of the optical afterglow is insignificant. [ABSTRACT FROM AUTHOR]

The motion with intersections of relativistic gravitating shells in the Schwarzschild gravitational field of a central body is considered. Formulas are derived for calculating parameters of the shells after intersection via their parameters before intersection. Such special cases as the Newtonian approximation, intersections of light shells, and intersections of a test shell with a gravitating shell are also considered. The ejection of one of the shells to infinity in the relativistic region is described. The equations of motion for the shells are analyzed numerically. [ABSTRACT FROM AUTHOR]

The evolution of stars with mass 5M⊙ with an initially cool neutron core (Thorne-Zytkow objects) is computed numerically, taking into account the heating of the neutron star by flows of heat released during the accretion of a surrounding envelope. The temperature of the neutron core does not rise to values at which the system could become unstable to rapid increases in the neutrino luminosity. In other words, the heating of the neutron core does not lead to a rapid collapse of the initial configuration. [ABSTRACT FROM AUTHOR]

This paper studies holey graphene with various neck widths (the smallest distance between two neighbor holes). For the considered structures, the energy gap, the Fermi level, the density of electronic states, and the distribution of the local density of electronic states (LDOS) were found. The electroconductive properties of holey graphene with round holes were calculated depending on the neck width. It was found that, depending on the neck width, holey graphene demonstrated a semiconductor type of conductivity with an energy gap varying in the range of 0.01–0.37 eV. It was also shown that by changing the neck width, it is possible to control the electrical conductivity of holey graphene. The anisotropy of holey graphene electrical conductivity was observed depending on the direction of the current transfer. [ABSTRACT FROM AUTHOR]

Relativistic shocks propagating into a medium with low magnetization are generated and sustained by small-scale but very strong magnetic field turbulence. This so-called "microturbulence" modifies the typical shock acceleration process, and in particular that of electrons. In this work we perform Monte Carlo (MC) simulations of electrons encountering shocks with microturbulent fields. The simulations cover a three-dimensional parameter space in shock speed, acceleration efficiency, and peak magnetic field strength. From these, a Markov Chain Monte Carlo (MCMC) method was employed to estimate the maximum electron momentum from the MC-simulated electron spectra. Having estimated this quantity at many points well-distributed over an astrophysically relevant parameter space, an MCMC method was again used to estimate the parameters of an empirical formula that computes the maximum momentum of a Fermi-accelerated electron population anywhere in this parameter space. The maximum energy is well-approximated as a broken power law in shock speed, with the break occurring when the shock decelerates to the point where electrons can begin to escape upstream from the shock. [ABSTRACT FROM AUTHOR]

Active galactic nuclei with misaligned jets have been recently established as a class of high-energy gamma-ray sources. M87, a nearby representative of this class, shows fast TeV variability on timescales less than one day. We present calculations performed in the framework of the scenario in which gamma-ray flares in non-blazar active galactic nuclei are produced by a red giant or a gas cloud interacting with the jet. We show that both the light curve and energy spectrum of the spectacular 2010 April flare can be reproduced by this model, assuming that a relatively massive cloud of ∼1029 g penetrates into the jet at few tens of Schwarzschild radii from the supermassive black hole. [ABSTRACT FROM AUTHOR]

Guar gum is a polymer that is widely used as a gelling agent for technological liquids in the petroleum industry. In this work, we have studied the potential for the environmentally friendly biodegradation of guar gum by enzymes of basidiomycetes for efficient disposal of oil industry wastes. We compared the enzymatic activity against guar gum of seven basidiomycete strains for the first time, namely Trametes hirsute MT-24.24, Lactarius necator, T. hirsute MT-17.24, Schizophyllum commune MT-33.01, Fomes fomentarius MT-4.05, Fomitopsis pinicola MT-5.21, and T. versicolor It-1. This comparison showed that the preparation based on the Fomitopsis pinicola MT-5.21 fungal mycelium at a concentration of 0.05% provides the most efficient decomposition of a hydraulic fracturing fluid containing guar gum. By varying the enzyme concentration in this fluid, it is possible to control the decrease in its viscosity over time. The developed enzyme preparation is an efficient and environmentally friendly guar gum biodegrader and can serve for processing waste fracturing fluids based on polysaccharides in order to reuse water resources. [ABSTRACT FROM AUTHOR]

Engineering the physics and chemistry of 2D materials is a key to unlock the potential of the advanced e‐nose technologies limited by the current semiconductor technologies. Herein, the adjustment of the graphene's morphology, physics, and gas sensing properties upon its carboxylation via the developed photochemical method is demonstrated. Formation of matrices of nanoscale holes yet with the retention of the lamellar structure of the graphene layer is signified upon the introduction of up to 9.5 at% of carboxyl groups. The impact of the applied carboxylation on the conduction mechanism and electronic structure is demonstrated. The appearance of a set of the localized states in the valence band is revealed, originating from the molecular orbitals of carboxyls as is signified by the proposed approach for the identification of electronic states in graphene chemical derivatives. Given holey structure, predominance of highly affine carboxyls, and lateral inhomogeneity, the enhanced detection and discrimination of various alcohols, acetone, and ammonia vapors at room temperature is demonstrated. The opposite chemiresistive response toward ammonia in the humid air is also experimentally revealed and justified by the performed density functional theory modeling on the effect of ammonia, water, and their mix on electronic structure, and resistivity of the carboxylated graphene. [ABSTRACT FROM AUTHOR]

Context. Extragalactic jets are formed close to supermassive black-holes in the center of galaxies. Large amounts of gas, dust, and stars cluster in the galaxy nucleus, and interactions between this ambient material and the jet base should be frequent, having dynamical as well as radiative consequences. Aims. This work studies the dynamical interaction of an obstacle, a clump of matter or the atmosphere of an evolved star, with the innermost region of an extragalactic jet. Jet mass-loading and the high-energy outcome of this interaction are briefly discussed. Methods. Relativistic hydrodynamical simulations with axial symmetry have been carried out for homogeneous and inhomogeneous obstacles inside a relativistic jet. These obstacles may represent a medium inhomogeneity or the disrupted atmosphere of a red giant star. Results. Once inside the jet, an homogeneous obstacle expands and gets disrupted after few dynamical timescales, whereas in the inhomogeneous case, a solid core can smoothen the process, with the obstacle mass-loss dominated by a dense and narrow tail pointing in the direction of the jet. In either case, matter is expected to accelerate and eventually get incorporated to the jet. Particles can be accelerated in the interaction region, and produce variable gamma-rays in the ambient matter, magnetic and photon fields. Conclusions. The presence of matter clumps or red giants into the base of an extragalactic jet likely implies significant jet massloading and slowing down. Fast flare-like gamma-ray events, and some level of persistent emission, are expected due to these interactions. [ABSTRACT FROM AUTHOR]

Topological models of graphene/CNT composite films are constructed. The films consist of tubes lying irregularly between graphene single layers parallel to them and covalently bound with graphene. The distance between the tubes is measured in graphene hexagons (H1 and H2) between ribs participating in the formation of covalent bonds. It is shown that only films based on zigzag (n, 0)-type tubes with an even number n are energetically stable. The film with the tube (10.0) and arrangement step 6/8 is most stable according to the investigations. It is found that the energy gap is present in the band structure of all studied film models and is in the range of 0.41–0.73 eV. [ABSTRACT FROM AUTHOR]