We use the Monte Carlo particle physics code FLUKA to calculate γ-ray spectra expected from solar flare energetic ion distributions. The FLUKA code includes robust physics-based models for electromagnetic, hadronic, and nuclear interactions, sufficiently detailed for it to be a useful tool for calculating nuclear de-excitation, positron annihilation and neutron capture line fluxes and shapes, as well as ~GeV continuum radiation from pion decay products. We show γ-ray model spectra which exhibit all the typical structures of γ-ray spectra observed in solar flares. From these model spectra we build templates which are incorporated into the software package OSPEX and used to fit the joint Fermi Gamma-ray Burst Monitor (GBM)/Large Area Telescope (LAT) spectrum of the 2010 June 12 solar flare, providing a statistically acceptable result.

For the first time, based on the experimental data of AMS-02, a three-parameter spectrum of variations of ga - lactic cosmic rays was obtained in the range of rigidity 1- 20 GV, to which neutron monitors are most sensitive. It was found that during the period of negative polarity of the solar magnetic field, a power-law spectrum of va - riations is observed with a strong exponential decay in the region of high rigidity. When the polarity changes to positive at the beginning of the new 24th solar cycle, the spectrum of cosmic ray variations becomes purely po- wer-law. The transition to the experimentally obtained spectrum of variations will make it possible to remove a number of uncertainties and increase the accuracy of the analysis of data from the ground network of detectors. This will make it possible to retrospectively obtain fluxes of galactic protons with an average monthly resolution for the period of the space era based on ground-based monitoring.

Gamma-ray continuum at $> 10 $ MeV photon energy yields information on $\gtrsim 0.2 $  – 0.3 GeV/nucleon ions at the Sun. We use the general-purpose Monte Carlo code FLUktuierenden KAskade (FLUKA) to model the transport of ions injected into thick and thin target sources, the nuclear processes that give rise to pions and other secondaries and the escape of the resulting photons from the atmosphere. We give examples of photon spectra calculated with a range of different assumptions about the primary ion velocity distribution and the source region. We show that FLUKA gives results for pion decay photon emissivity in agreement with previous treatments. Through the directionality of secondary products, as well as Compton scattering and pair production of photons prior to escaping the Sun, the predicted spectrum depends significantly on the viewing angle. Details of the photon spectrum in the $\approx 100$ MeV range may constrain the angular distribution of primary ions and the depths at which they interact. We display a set of thick-target spectra produced making various assumptions about the incident ion energy and angular distribution and the viewing angle. If ions are very strongly beamed downward, or ion energies do not extend much above 1 GeV/nucleon, the photon spectrum is highly insensitive to details of the ion distribution. Under the simplest assumptions, flares observed near disc centre should not display significant radiation above 1 GeV photon energy. We give an example application to Fermi Large Area Telescope data from the flare of 12 June 2010.

AbstractRecent observations of solar flares at high frequencies have provided evidence of a new spectral component with flux increasing with frequency in the THz range. Its origin remains unclear. Here, we present preliminary results of simulations of synchrotron emission due to secondary positrons and electrons produced in nuclear reactions during a solar flare. We use the general purpose Monte-Carlo code FLUKA to obtain distributions of secondary particles resulting from accelerated protons interacting in the solar atmosphere. We calculate the synchrotron radiation spectrum and compare our results to observations of the November 4th, 2003 burst event.

We consider the problem of transport through a multiterminal molecular junction in the presence of a stochastic bias, which can also be used to describe transport through fluctuating molecular energy levels. To describe these effects, we first make a simple extension of our previous work [Phys. Rev. B 91, 125433 (2015)] to show that the problem of tunneling through noisy energy levels can be mapped onto the problem of a noisy driving bias, which appears in the Kadanoff-Baym equations for this system in an analogous manner to the driving term in the Langevin equation for a classical circuit. This formalism uses the nonequilibrium Green's function method to obtain analytically closed formulas for transport quantities within the wide-band limit approximation for an arbitrary time-dependent bias and it is automatically partition free. We obtain exact closed formulas for both the colored and white noise-averaged current at all times. In the long-time limit, these formulas possess a Landauer-Buttiker-type structure which enables the extraction of an effective transmission coefficient for the transport. Expanding the Fermi function into a series of simple poles, we find an exact formal relation between the parameters which characterize the bias fluctuations and the poles of the Fermi function. This enables us to describe the effect of the temperature and the strength of the fluctuations on the averaged current which we interpret as a quantum analog to the classical fluctuation-dissipation theorem. We use these results to convincingly refute some recent results on the multistability of the current through a fluctuating level, simultaneously verifying that our formalism satisfies some well-known theorems on the asymptotic current. Finally, we present numerical results for the current through a molecular chain which demonstrate a transition from nonlinear to linear I-V characteristics as the strength of fluctuations is increased, as well as a stochastic resonance effect in the conductance of this system.

We apply the nonequilibrium Green's function formalism to the problem of a multiterminal nanojunction subject to an arbitrary time-dependent bias. In particular, we show that taking a generic one-particle system Hamiltonian within the wide-band-limit approximation, it is possible to obtain a closed analytical expression for the current in each lead. Our formula reduces to the well-known result of Jauho et al. [Phys. Rev. B 50, 5528 (1994)] in the limit where the switch-on time is taken to the remote past, and to the result of Tuovinen et al. [Phys. Rev. B 89, 085131 (2014)] when the bias is maintained at a constant value after the switch-on. As we use a partition-free approach, our formula contains both the long-time current and transient effects due to the sudden switch-on of the bias. Numerical calculations performed for the simple case of a single-level quantum dot coupled to two leads are performed for a sinusoidally varying bias. At certain frequencies of the driving bias, we observe "ringing" oscillations of the current, whose dependence on the dot level, level width, oscillation amplitude, and temperature is also investigated.

The Sun is an active source of radio emission which is often associated with energetic phenomena such as solar flares and coronal mass ejections (CMEs). At low radio frequencies (<100 MHz), the Sun has not been imaged extensively because of the instrumental limitations of previous radio telescopes. Here, the combined high spatial, spectral and temporal resolution of the Low Frequency Array (LOFAR) was used to study solar Type III radio bursts at 30-90 MHz and their association with CMEs. The Sun was imaged with 126 simultaneous tied-array beams within 5 solar radii of the solar centre. This method offers benefits over standard interferometric imaging since each beam produces high temporal (83 ms) and spectral resolution (12.5 kHz) dynamic spectra at an array of spatial locations centred on the Sun. LOFAR's standard interferometric output is currently limited to one image per second. Over a period of 30 minutes, multiple Type III radio bursts were observed, a number of which were found to be located at high altitudes (4 solar radii from the solar center at 30 MHz) and to have non-radial trajectories. These bursts occurred at altitudes in excess of values predicted by 1D radial electron density models. The non-radial high altitude Type III bursts were found to be associated with the expanding flank of a CME. The CME may have compressed neighbouring streamer plasma producing larger electron densities at high altitudes, while the non-radial burst trajectories can be explained by the deflection of radial magnetic fields as the CME expanded in the low corona.

We apply the Nonequilibrium Green's Function (NEGF) formalism to the problem of a multi-terminal nanojunction subject to an arbitrary time-dependent bias. In particular, we show that taking a generic one-particle system Hamiltonian within the wide band limit approximation (WBLA), it is possible to obtain a closed analytical expression for the current in each lead. Our formula reduces to the well-known result of Jauho et. al. [doi:10.1103/PhysRevB.50.5528] in the limit where the switch-on time is taken to the remote past, and to the result of Tuovinen et. al. [doi:10.1088/1742-6596/427/1/012014] when the bias is maintained at a constant value after the switch-on. As we use a partition-free approach, our formula contains both the long-time current and transient effects due to the sudden switch-on of the bias. Numerical calculations performed for the simple case of a single-level quantum dot coupled to two leads are performed for a sinusoidally-varying bias. At certain frequencies of the driving bias, we observe `ringing' oscillations of the current, whose dependence on the dot level, level width, oscillation amplitude and temperature is also investigated.

We discuss the implications of the first systematic observations of solar flares at submillimeter wavelengths, defined here as observing wavelengths shorter than 3 mm (frequencies higher than 0.1 THz). The events observed thus far show that this wave band requires a new understanding of high-energy processes in solar flares. Several events, including observations from two different observatories, show during the impulsive phase of the flare a spectral component with a positive (increasing) slope at the highest observable frequencies (up to 405 GHz). To emphasize the increasing spectra and the possibility that these events could be even more prominent in the THz range, we term this spectral feature a “THz component”. Here we review the data and methods, and critically assess the observational evidence for such distinct component(s). This evidence is convincing. We also review the several proposed explanations for these feature(s), which have been reported in three distinct flare phases. These data contain important clues to flare development and particle acceleration as a whole, but many of the theoretical issues remain open. We generally have lacked systematic observations in the millimeter-wave to far-infrared range that are needed to complete our picture of these events, and encourage observations with new facilities.

Context. The presence of energetic X-ray sources in the solar corona indicates there are additional transport effects in the acceleration region. A prime method of investigation is to add collisions into models of particle behaviour at the reconnection region. Aims. We investigate electron test particle acceleration in a simple model of an X-type reconnection region. In particular, we explore the possibility that collisions will cause electrons to re-enter the acceleration more frequently, in turn causing particles to be accelerated to high energies. Methods. The deterministic (Lorentz) description of particle gyration and acceleration has been coupled to a model for the effects of collisions. The resulting equations are solved numerically using Honeycutt’s extension of the RK4 method to stochastic differential equations. This approach ensures a correct description of collisional energy loss and pitch-angle scattering combined with a sufficiently precise description of gyro-motion and acceleration. Results. Even with initially mono-energetic electrons, the competition between collisions and acceleration results in a distribution of electron energies. When realistic model parameters are used, electrons achieve X-ray energies. A possible model for coronal hard X-ray sources is indicated. Conclusions. Even in competition with energy losses, pitch-angle scattering results in a small proportion of electrons reaching higher energies than they would in a collisionless situation.

We apply local intermittency measure (LIM) analysis to 64 ms time resolved BATSE measurements of hard X-rays from several solar flares. LIM analysis yields information on the character of the processes giving rise to fluctuations in light curves, e. g. avalanche vs. cascade pictures. We present LIM scaleograms for several flares and summarise scaleogram morphological features. More detailed descriptions are given of the behaviour in the flare of 13 January 1992 (the well-known 'Masuda flare') and an interesting event on 22 November 1998. All flares display episodes of intermittency across a range of scales. LIM scaleogram features may be consistent with both 'top-down' and 'bottom-up' scenarios for the development of small-scale structure, sometimes within the same flare. Thus neither class of model captures the totality of the events in a flare.

Charge-exchange reactions at high energies provide new channels for the remote sensing of solar high-energy particles, as demonstrated by the recent detection of 1.8-5 MeV hydrogen atoms from a solar flare [1]. Orrall and Zirker [2] had earlier proposed the detection of low-energy protons via charge-exchange atomic reactions in the solar atmosphere, leading in the simplest case to extended red-wing emission in the Lyman-alpha line. We discuss the analogous process for the He II 304 angstrom line (for alpha particles) and also assess the feasibility of the analogous process in the solar wind, whereby ambient He and (C, N, O) ions allow low-energy alpha particles to undergo resonant charge exchange in the ambient corona and thereby produce 304 angstrom wing emission close to the acceleration region.

We introduce the local intermittency measure (LIM) as a tool for the investigation of solar flare hard X-ray light curves. Constructed from wavelet amplitudes, the LIM allows us to investigate the extent to which rapid fluctuations reveal an underlying, scale-invariant process, and to identify those episodes during a flare which definitely represent ‘intermittent’ behaviour (e.g. involvement of new spatial structures). We carry out two sets of simple simulations intended to provide generic examples of ‘top-down’ and ‘bottom-up’ scenarios for the development of flares, and show how LIM may discriminate between them.

We simulate the likely noisy situation near a reconnection region by superposing many 2D linear reconnection eigenmodes. The superposition of modes on the steady state X-type magnetic field creates multiple X- and O-type neutral points close to the original neutral point and so increases the size of the non-adiabatic region. We study test particle trajectories of initially thermal protons in these fields. Protons become trapped in this region and are accelerated by the turbulent electric field to energies up to 1 MeV in time scales relevant to solar flares. Higher energies are achieved due to the interaction of particles with increasingly turbulent electric and magnetic fields.

Gamma-rays and neutrons are the only sources of information on energetic ions present during solar flares and on properties of these ions when they interact in the solar atmosphere. The production of γ-rays and neutrons results from convolution of the nuclear cross-sections with the ion distribution functions in the atmosphere. The observed γ-ray and neutron fluxes thus provide useful diagnostics for the properties of energetic ions, yielding strong constraints on acceleration mechanisms as well as properties of the interaction sites. The problem of ion transport between the accelerating and interaction sites must also be addressed to infer as much information as possible on the properties of the primary ion accelerator. In the last couple of decades, both theoretical and observational developments have led to substantial progress in understanding the origin of solar γ-rays and neutrons. This chapter reviews recent developments in the study of solar γ-rays and of solar neutrons at the time of the RHESSI era. The unprecedented quality of the RHESSI data reveals γ-ray line shapes for the first time and provides γ-ray images. Our previous understanding of the properties of energetic ions based on measurements from the former solar cycles is also summarized. The new results—obtained owing both to the gain in spectral resolution (both with RHESSI and with the non solar-dedicated INTEGRAL/SPI instrument) and to the pioneering imaging technique in the γ-ray domain—are presented in the context of this previous knowledge. Still open questions are emphasized in the last section of the chapter and future perspectives on this field are briefly discussed.

Context. Recently, unanticipated magnetic activity in ultracool dwarfs (UCDs, spectral classes later than M7) has emerged from a number of radio observations. The highly (up to 100%) circularly polarized nature and high brightness temperature of the emission have been interpreted as requiring an effective amplification mechanism of the high-frequency electromagnetic waves - the electron cyclotron maser instability (ECMI).Aims. We aim to understand the magnetic topology and the properties of the radio emitting region and associated plasmas in these ultracool dwarfs, interpreting the origin of radio pulses and their radiation mechanism.Methods. An active region model was built, based on the rotation of the UCD and the ECMI mechanism.Results. The high degree of variability in the brightness and the diverse profile of pulses can be interpreted in terms of a large-scale hot active region with extended magnetic structure existing in the magnetosphere of TVLM 513-46546. We suggest the time profile of the radio light curve is in the form of power law in the model. Combining the analysis of the data and our simulation, we can determine the loss-cone electrons have a density in the range of 1.25x 10(5)-5 x 10(5) cm(-3) and temperature between 10(7) and 5 x 10(7) K. The active region has a size <1 R-Jup, while the pulses produced by the ECMI mechanism are from a much more compact region (e.g. similar to 0.007 R-Jup). A surface magnetic field strength of approximate to 7000 G is predicted.Conclusions. The active region model is applied to the radio emission from TVLM 513-46546, in which the ECMI mechanism is responsible for the radio bursts from the magnetic tubes and the rotation of the dwarf can modulate the integral of flux with respect to time. The radio emitting region consists of complicated substructures. With this model, we can determine the nature (e. g. size, temperature, density) of the radio emitting region and plasma. The magnetic topology can also be constrained. We compare our predicted X-ray flux with Chandra X-ray observation of TVLM 513-46546. Although the X-ray detection is only marginally significant, our predicted flux is significantly lower than the observed flux. Further multi-wavelength observations will help us better understand the magnetic field structure and plasma behavior on the ultracool dwarf.

In this work, we determine the effects of temperature on the magnetoplasmon spectrum of an electrically modulated graphene monolayer as well as a two-dimensional electron gas (2DEG). The intra-Landau band magnetoplasmon spectrum within the self-consistent field approach is investigated for both the aforementioned systems. Results obtained not only exhibit Shubnikov–de Haas (SdH) oscillations but also commensurability oscillations (Weiss oscillations). These oscillations are periodic as a function of inverse magnetic field. We find that both the magnetic oscillations, SdH and Weiss, have a greater amplitude and are more robust against temperature in graphene compared to a conventional 2DEG. Furthermore, there is a π phase shift between the magnetoplasmon oscillations in the two systems which can be attributed to Dirac electrons in graphene acquiring a Berry's phase as they traverse a closed path in a magnetic field.

Context. A fundamental problem in astrophysics is the interaction between magnetic turbulence and charged particles. It is now possible to use Ramaty High Energy Solar Spectroscopic Imager (RHESSI) observations of hard X-rays (HXR) emitted by electrons to identify the presence of turbulence and to estimate the magnitude of the magnetic field line diffusion coefficient at least in dense coronal flaring loops. Aims. We discuss the various possible regimes of cross-field transport of non-thermal electrons resulting from broadband magnetic turbulence in coronal loops. The importance of the Kubo number K as a governing parameter is emphasized and results applicable in both the large and small Kubo number limits are collected. Methods. Generic models, based on concepts and insights developed in the statistical theory of transport, are applied to the coronal loops and to the interpretation of hard X-ray imaging data in solar flares. The role of trapping effects, which become important in the non-linear regime of transport, is taken into account in the interpretation of the data. Results. For this flaring solar loop, we constrain the ranges of parallel and perpendicular correlation lengths of turbulent magnetic fields and possible Kubo numbers. We show that a substantial amount of magnetic fluctuations with energy ∼1% (or more) of the background field can be inferred from the measurements of the magnetic diffusion coefficient inside thick-target coronal loops.

We present a theoretical study of time-dependent transport via a quantum shuttle within the non-equilibrium Green's function technique. An arbitrary voltage is applied to the tunnel junction and electrons in the leads are considered to be at zero temperature. The transient and the steady state behavior of the system is considered here in order to explore the quantum dynamics of the shuttle device as a function of time and applied bias. The properties of the phonon distribution of the oscillating dot coupled to the electrons are investigated using a non-perturbative approach. We derive a relation for the oscillator momentum charge density correlation function which is an interesting physical example for the visualization of shuttling phenomenon. We consider the crossover between the tunneling and shuttling regimes for different values of the key parameters as a function of applied bias and time. We also consider the energy transferred from the electrons to the oscillating dot as a function of time. This will provide useful insight for the design of experiments aimed at studying the quantum behavior of a shuttling device.

Eduard Kontar, eduard@astro.gla.ac.uk University of Glasgow, Glasgow, United Kingdom Alexander MacKinnon, a.mackinnon@educ.gla.ac.uk University of Glasgow, GLASGOW, United Kingdom Karl-Ludwig Klein, ludwig.klein@obspm.fr Observatoire de Paris, Meudon, France Nicole Vilmer, nicole.vilmer@obspm.fr Observatoire de Paris, LESIA, Meudon, France Lucie M. Green, lmg@mssl.ucl.ac.uk Mullard Space Science Laboratory, University College, Holmbury St.Mary. Dorking, United Kingdom Sarah A. Matthews, sam@mssl.ucl.ac.uk Mullard Space Science Laboratory, University College, Holmbury St.Mary. Dorking, United Kingdom