Hot Protons Research Articles

Poloidal ULF wave observed in the plasmasphere boundary layer

AbstractWe report on a rare ultra‐low‐frequency (ULF) wave generation event associated with the formation of a plasmasphere boundary layer (PBL), which was well observed by one of the THEMIS satellites, TH‐D, during subsequent outbound passes. On 13 September 2011, TH‐D observed a sharp plasmapause at L = 3.4. The plasmasphere started to expand and continued to be refilled on 14 September. On 15 September, a PBL was formed with two density gradients at L = 4.4 and 6.5, respectively. Within the two density gradients, strong radial magnetic field and azimuthal electric field oscillations were observed, suggesting poloidal ULF waves. Based on the phase delay between magnetic and electric field signals, as well as the comparison between the observed wave frequency and predicted harmonic eigenfrequency, we find that the observed oscillations are second harmonic poloidal waves. Further investigation shows that the observed waves are likely generated by drift‐bounce resonance with “bump‐on‐tail” plasma distributions at ~10 keV. We demonstrate that the waves are excited within the PBL where the eigenfrequency is close to the bounce frequency of these hot protons, but not outside the PBL where the eigenfrequency deviates from the bounce frequency. Finally, we suggest that cold plasma density seems to be a controlling factor for ULF wave generation as well, in addition to the bump‐on‐tail energy source, by altering eigenfrequency of the local field lines.

Impact of cold O+ ions on the generation and evolution of EMIC waves

We explore the effect of cool O+ ions (~11 eV) on the generation and nonlinear evolution of electromagnetic ion cyclotron (EMIC) waves in the magnetosphere, using hybrid (kinetic ions, fluid electrons) simulations with a dipolar magnetic field. The instability is driven by the temperature anisotropy of the hot (keV), ring current protons whose density is a few percent of the background plasma consisting of cold (eV) protons and O+ ions with concentrations varying between 0 and 30% of the cold protons. The results show that for O+ ion concentration of 7% or less, the properties of the EMIC waves are similar to those in the absence of O+ ions where waves are generated at low latitudes and propagate all the way to the ionospheric boundary. Further increases in O+ density (~15%) result in waves being confined in latitude due to processes explored in this paper. At O+ densities of 30% and higher, the growth of EMIC waves is weak or non‐existent due to cyclotron resonant damping by the O+ ions. Comparing the results of the runs with no and 15% O+ ions shows that the propagation properties of the EMIC waves change dramatically in the presence of O+ ions. Specifically, they show that waves are propagating parallel and anti‐parallel to the magnetic field in both hemispheres due to reflection at points that move to higher latitudes with time. This in turn results in the nonlinear generation of field aligned electrostatic waves with large perturbations in the density of the cold protons and O+ ions and also local heating of these ions. Examination of the wave properties also shows that EMIC waves are only present in regions of space where the density of the hot protons is larger than 1% of the background level. In other words, the propagation properties of the EMIC waves are controlled by the density of the hot protons. This finding is further confirmed by performing a test hybrid simulation in which hot protons reaching latitude of 22° are removed from the run resulting in the confinement of the waves to this and lower latitudes.

Hydrogen transport diagnostics by atomic and molecular emission line profiles simultaneously measured for large helical device

We observe the Balmer-α, -β, and -γ lines of hydrogen atoms and Q branches of the Fulcher-α band of hydrogen molecules simultaneously with their polarization resolved for large helical device. From the fit including the line splits and the polarization dependences by the Zeeman effect, the emission locations, intensities, and the temperatures of the atoms and molecules are determined. The emission locations of the hydrogen atoms are determined outside but close to the last closed flux surface (LCFS). The results are consistent with a previous work (Phys. Plasmas 12, 042501 (2005)). On the other hand, the emission locations of the molecules are determined to be in the divertor legs, which is farer from those of the atoms. The kinetic energy of the atoms is 1 ∼ 20 eV, while the rotational temperature of molecules is ∼0.04 eV. Additionally, substantial wings, which originate from high velocity atoms and are not reproduced by the conventional spectral analysis, are observed in the Balmer line profiles. We develop a one-dimensional model to simulate the transport of the atoms and molecules. The model reproduces the differences of the emission locations of the atoms and molecules when their initial temperatures are assumed to be 3 eV and 0.04 eV, respectively. From the model, the wings of the Balmer-α line is attributed to the high velocity atoms exist deep inside the LCFS, which are generated by the charge exchange collisions with hot protons there.

Precipitation of highly energetic protons by helium branch electromagnetic ion cyclotron triggered emissions

In the equatorial region of the Earth's inner magnetosphere, the electromagnetic ion cyclotron (EMIC) triggered emissions are generated through interaction with energetic protons. We investigate the generation process of the EMIC triggered emissions in the He+branch and associated precipitation of the energetic protons using a one‐dimensional hybrid simulation with a cylindrical parabolic magnetic geometry. The simulation results show a good agreement with the nonlinear wave growth theory. As the electron density becomes higher as in the plasmasphere or the plasmaplume, the wave amplitude thresholds for both H+ and He+ band triggered emissions become lower and their nonlinear growth rates become higher. The higher hot proton density also makes the thresholds lower. While the H+ branch triggered emissions interact with a few keV protons, the He+ branch triggered emissions interact with more energetic protons of a few hundred keV with a larger nonlinear growth rate.

COLLISIONLESS SHOCKS IN A PARTIALLY IONIZED MEDIUM. II. BALMER EMISSION

Strong shocks propagating into a partially ionized medium are often associated with optical Balmer lines. This emission is due to impact excitation of neutral hydrogen by hot protons and electrons in the shocked gas. The structure of such Balmer-dominated shocks has been computed in a previous paper (Blasi et al. 2012), where the distribution function of neutral particles was derived from the appropriate Boltzmann equation including coupling with ions and electrons through charge exchange and ionization. This calculation showed how the presence of neutrals can significantly modify the shock structure through the formation of a "neutral-induced" precursor ahead of the shock. Here we follow up on our previous work and investigate the properties of the resulting Balmer emission, with the aim of using the observed radiation as a diagnostic tool for shock parameters. Our main focus is on Supernova Remnant shocks, and we find that, for typical parameters, the H{\alpha} emission typically has a three-component spectral profile, where: 1) a narrow component originates from upstream cold hydrogen atoms, 2) a broad component comes from hydrogen atoms that have undergone charge exchange with shocked protons downstream of the shock, and 3) an intermediate component is due to hydrogen atoms that have undergone charge exchange with warm protons in the neutral-induced precursor. The width of the intermediate line reflects the temperature in the precursor, while the width of the narrow one is left unaltered by the precursor. In addition, we show that the profiles of both the intermediate and broad components generally depart from a thermal distribution. Finally, we show that a significant amount of Balmer emission can be produced in the precursor region if efficient electron heating takes place.

Hybrid simulations of EMIC waves in a dipolar magnetic field

[1] We employ 2.5-D electromagnetic, hybrid simulations that treat ions kinetically via particle-in-cell methods and electrons as a massless fluid to study the generation, propagation and nonlinear evolution of electromagnetic ion cyclotron (EMIC) waves in a dipolar magnetic field. The source of the instability is a small population of hot (keV) protons, representing the ring current ions injected in the equatorial region throughout the run. In this paper we investigate the impacts of the level of temperature anisotropy of these source ions, as well as the location of their injection on the EMIC wave excitation. We simulate wave generation using a ratio of perpendicular to parallel temperature ranging between 4 and 1.6 and show that parallel propagating EMIC waves with circular polarization are generated in the equatorial regions at frequencies below the proton cyclotron frequency. Examination of the Poynting vector shows that waves propagate along the magnetic field away from the equator and reach the ionospheric boundary where they are absorbed due to the simulation boundary conditions. Wave reflection does not occur anywhere along the path of propagation between the equator and the ionosphere. Refraction due to magnetic field gradients results in waves becoming more oblique as they propagate to higher latitudes. As a result, their polarization also changes with one transverse component vanishing and the development of a compressional component. The results also show a reduction in the total density and magnetic field in the region of EMIC wave generation. Although the reduction in density is partially due to the pressure associated with the injection of the hot protons, we show that EMIC waves contribute considerably to the level of density reduction. The nonlinear evolution of the EMIC waves results in the generation of field aligned electrostatic waves in the equatorial and low latitude regions. It is also shown that changing the level of temperature anisotropy while keeping the injection region fixed not only affects the maximum amplitudes reached but also the region of wave growth. Similarly, for a given temperature anisotropy the results vary as the injection region is changed.

Saturation characteristics of electromagnetic ion cyclotron waves

[1] Electromagnetic ion cyclotron (EMIC) waves are an integral component of the Earth's dynamic space environment. In order to quantify their effect, it is necessary to know their saturation amplitude, but in modeling studies it is usually the linear growth rate that is calculated and various assumptions need to be made in order to relate this growth rate to the final amplitude of the wave. Here, we perform a comparison of the saturation characteristics of EMIC waves using a 2.5-D electromagnetic hybrid PIC code, with the corresponding linear growth rates calculated with the hot-plasma dispersion solver of the HOTRAY code. We choose a set of values consistent with satellite observations for our nominal case, and explore the parameter space in the neighborhood of this nominal case, by varying the hot proton density and thermal anisotropy. We find that the saturation amplitudes increase monotonically, and the times to saturation decrease monotonically with increasing growth rates, independent of the values of density and anisotropy. Both the saturation amplitude and time to saturation curves can be fit by simple two-parameter models with acceptable errors. This result implies that within the limitations and caveats of the present study, the saturation amplitudes and time to saturation can be predicted with good accuracy based on the linear growth rates alone, which can be used directly in conjunctions with global ring current simulations to model the resultant effects on magnetospheric particles.

Effects of superthermal ring current ion tails on the electromagnetic ion cyclotron instability in multi-ion magnetospheric plasmas

[1] An important plasma source for the storm-enhanced ring current is the plasma sheet. Ion species in the near-Earth plasma sheet have been observed to have power law tails on their velocity distributions, which can be well fitted with kappa distributions under a variety of geomagnetic conditions. Motivated by these ideas, we investigate the electromagnetic ion cyclotron (EMIC) instability driven by hot ring current ions having velocity distributions that exhibit thermal anisotropy and power law tails of varying degrees of hardness (smallness of power index) for parameters consistent with the inner magnetosphere. With few exceptions, the presence of hard power law tails on the velocity distributions of the ring current ion species is observed to significantly enhance instability growth rates relative to a bi-Maxwellian ring current model. For a ring current composed of only hot protons, all EMIC branches are unstable, with the helium branch exhibiting the fastest growth rate for the thermal anisotropies considered. The addition of equal number densities of helium and oxygen ions to the ring current plasma has a dramatic stabilizing effect on the proton and helium branches. In this case it is frequently only the oxygen branch of the EMIC wave dispersion relation which is unstable. The detailed balance between cyclotron damping produced by one species and growth produced by another elevates the importance of the velocity distribution spectral index so that it can serve as a “switch” to turn on instability of certain branches.

Nonlinear evolution of EMIC waves in a uniform magnetic field: 1. Hybrid simulations

We employ 2.5‐D electromagnetic, hybrid simulations that treat ions kinetically via particle‐in‐cell methods and electrons as a massless fluid to study the long‐term (hours) nonlinear evolution of electromagnetic ion cyclotron waves in the presence of multiple ion species in the outer magnetosphere. The source of the instability is a small population of hot (few keV) protons, representing plasma sheet ions at L = 9 with perpendicular temperature four times the parallel. In addition to the background population of cold protons the presence of minority, cold and heavy ions such as helium are also included. Both local (homogeneous) and nonlocal (finite‐sized source region) simulations with uniform magnetic field have been carried out. In the case of a homogeneous system, parallel propagating ion cyclotron waves are generated with amplitudes of a few percent of the background magnetic field (a few nT). After about 1000 ion gyroperiods (∼4 min) the wave amplitudes decrease by about 50% and remain nearly constant thereafter. The nonlinear evolution of the waves is associated with the gyrophase bunching of the cold protons and helium ions and reduction in the temperature anisotropy of the hot protons. In addition, parallel electrostatic waves with a wavelength half of that of the ion cyclotron waves are generated. These waves are subsequently absorbed and result in parallel heating of the cold ions. Throughout the run, both cold protons and heavy ions continue to gain energy primarily in the perpendicular direction while the hot protons reach isotropy followed by cooling in both parallel and perpendicular directions. In effect, the ion cyclotron waves continue to facilitate transfer of energy from the hot to cold ions. The results of simulations with localized hot protons show the simultaneous generation of ion cyclotron waves and expansion of the source region along the magnetic field. The nonlinear evolution of the waves is found to be similar to that seen in the homogeneous runs.

Nonlinear evolution of EMIC waves in a uniform magnetic field: 2. Test‐particle scattering

The trajectories of individual proton test particles are computed as they traverse a temporally and spatially evolving electromagnetic ion cyclotron (EMIC) wavefield. This EMIC wavefield is simulated using a hybrid code, which is described in a companion paper, with parameters representative of those found in the dawnside outer magnetosphere (L ∼ 9). The scattering of a representative group of hot protons (E0 = 4 keV, α0 = 60°) and cool protons (E0 = 30 eV, α0 = 20°) is analyzed in configuration space, velocity space, E, α, and phase. Results indicate that the hot protons are scattered by the EMIC wave in a manner consistent with resonant wave‐particle interactions, that they are constrained to move along single‐wave characteristic curves, and that the particles experience moderate phase bunching. On the other hand, the cool protons are not scattered by the EMIC wave resonantly and experience strong phase bunching, which results in large positive advective motion in both E and α, as well as large relative diffusion. The phase bunching and heating of the cool proton population is consistent with observations of cool, heavy‐ion heating in space, and the phasing of the particle v⊥ and EMIC wave's E field is consistent with a previously described mechanism known as electric phase bunching, which results in efficient energization of cool particles.

A POSSIBLE GENERATION MECHANISM FOR THE IBEX RIBBON FROM OUTSIDE THE HELIOSPHERE

The brightest and most surprising feature in the first all-sky maps of Energetic Neutral Atoms (ENA) emissions (0.2-6 keV) produced by the Interstellar Boundary Explorer (IBEX) is an almost circular ribbon of a ~140{\deg} opening angle, centered at (l,b) = (33{\deg}, 55{\deg}), covering the part of the celestial sphere with the lowest column densities of the Local Interstellar Cloud (LIC). We propose a novel interpretation of the IBEX results based on the idea of ENA produced by charge-exchange between the neutral H atoms at the nearby edge of the LIC and the hot protons of the Local Bubble (LB). These ENAs can reach the Sun's vicinity because of very low column density of the intervening LIC material. We show that a plane-parallel or slightly curved interface layer of contact between the LIC H atoms (n_H = 0.2 cm^-3, T = 6000-7000 K) and the LB protons (n_p = 0.005 cm^-3, T ~ 10^6 K), together with indirect contribution coming from multiply-scattered ENAs from the LB, may be able to explain both the shape of the ribbon and the observed intensities provided that the edge is < (500-2000) AU away, the LIC proton density is (correspondingly) < (0.04-0.01) cm^-3, and the LB contains ~1% of non-thermal protons over the IBEX energy range. If this model is correct, then IBEX, for the first time, has imaged in ENAs a celestial object from beyond the confines of the heliosphere and can directly diagnose the plasma conditions in the LB.

Activation by lidocaine of TRPA1 channels in the substantia gelatinosa of adult rat spinal cord

Transient receptor potential (TRP) channels, nonselective cation channels, are gated by a variety of chemical and physical stimuli. Among them, there are TRPV1 and TRPA1 channels, both of which are thought to be involved in thermosensation and nociception. TRPV1 channels are activated by noxious hot temperature, protons and capsaicin while TRPA1 channels are by noxious cold temperature, mustard oil, cinnamon oil, ginger and garlic. These TRP channels are expressed in dorsal root ganglion (DRG) neurons; their activation in the central terminals of the neurons results in an increase in the spontaneous release of L-glutamate to spinal dorsal horn, particularly substantia gelatinosa (SG; lamina II of Rexed), neurons from nerve terminals. Although local anesthetics (LAs) were recently reported to activate TRP channels which are cloned and expressed in DRG neurons, this has not been thoroughly examined yet in the CNS. We examined the effects of amine-type LAs (lidocaine, ropivacaine, prilocaine and levobupivacaine) and ester-type LAs (procaine, tetracaine and pramoxine) on glutamatergic spontaneous excitatory synaptic transmission in SG neurons of adult rat spinal cord slices by using the whole-cell patch-clamp technique. Bath-applied lidocaine dose-dependently and reversibly increased the frequency but not the amplitude of spontaneous excitatory postsynaptic current (sEPSC) recorded at a holding potential of -70 mV in SG neurons. The effect of lidocaine was unaffected by the voltage-gated Na+-channel blocker, tetrodotoxin (TTX), and the TRPV1 channel antagonist, capsazepine (Capz), but was inhibited by the non-selective TRP channel antagonist, ruthenium red (RR). In the same neuron, the TRPA1 channel agonist, allyl isothiocyanate, and lidocaine both increased sEPSC frequency. Tetracaine also increased sEPSC frequency in SG neurons in a manner insensitive to TTX and Capz while sensitive to RR, an action similar to that of lidocaine, but this action was delayed in onset by about 2.5 min compared to that of lidocaine. Like lidocaine and tetracaine, pramoxine increased sEPSC frequency; prilocaine had a tendency to do so. On the contrary, procaine, ropivacaine and levobupivacaine reduced sEPSC frequency. It is concluded that some of the amine-type and ester-type LAs activate TRPA1 channels in the SG to increase the spontaneous release of L-glutamate from nerve terminals. This action could contribute to an increase in the excitability of SG neurons.

Transition from radiatively inefficient to cooling dominated phase in two temperature accretion disks around black holes

We investigate the transition of a radiatively inefficient phase of a viscous two temperature accreting flow to a cooling dominated phase and vice versa around black holes. Based on a global sub-Keplerian accretion disk model in steady state, including explicit cooling processes self-consistently, we show that general advective accretion flow passes through various phases during its infall towards a black hole. Bremsstrahlung, synchrotron and inverse Comptonization of soft photons are considered as possible cooling mechanisms. Hence the flow governs a much lower electron temperature ∼ 108 – 109.5 K compared to the hot protons of temperature ∼ 1010 2 – 1011.8 K in the range of the accretion rate in Eddington units 0.01 ≲ Ṁ ≲ 100. Therefore, the solutions may potentially explain the hard X-rays and the γ-rays emitted from AGNs and X-ray binaries. We finally compare the solutions for two different regimes of viscosity and conclude that a weakly viscous flow is expected to be cooling dominated compared to its highly viscous counterpart which is radiatively inefficient. The flow is successfully able to reproduce the observed luminosities of the under-fed AGNs and quasars (e.g. Sgr A*), ultra-luminous X-ray sources (e.g. SS433), as well as the highly luminous AGNs and ultra-luminous quasars (e.g. PKS 0743–67) at different combinations of the mass accretion rate and ratio of specific heats.

Two-temperature accretion around rotating black holes: a description of the general advective flow paradigm in the presence of various cooling processes to explain low to high luminous sources

We investigate the viscous two temperature accretion discs around rotating black holes. We describe the global solution of accretion flows with a sub-Keplerian angular momentum profile, by solving the underlying conservation equations including explicit cooling processes selfconsistently. Bremsstrahlung, synchrotron and inverse Comptonization of soft photons are considered as possible cooling mechanisms, for sub-Eddington, Eddington and super-Eddington mass accretion rates around Schwarzschild and Kerr black holes with a Kerr parameter 0.998. It is found that the flow, during its infall from the Keplerian to sub-Keplerian transition region to the black hole event horizon, passes through various phases of advection -- general advective paradigm to radiatively inefficient phase and vice versa. Hence the flow governs much lower electron temperature ~10^8-10^{9.5} K, in the range of accretion rate in Eddington units 0.01 <~ \mdot <~ 100, compared to the hot protons of temperature ~ 10^{10.2} - 10^{11.8}K. Therefore, the solution may potentially explain the hard X-rays and \gamma-rays emitted from AGNs and X-ray binaries. We then show that a weakly viscous flow is expected to be cooling dominated, particularly at the inner region of the disc, compared to its highly viscous counterpart which is radiatively inefficient. With all the solutions in hand, we finally reproduce the observed luminosities of the under-fed AGNs and quasars (e.g. Sgr A^*) to ultra-luminous X-ray sources (e.g. SS433), at different combinations of input parameters such as mass accretion rate, ratio of specific heats. The set of solutions also predicts appropriately the luminosity observed in the highly luminous AGNs and ultra-luminous quasars (e.g. PKS 0743-67).

Simulation of EMIC wave excitation in a model magnetosphere including structured high‐density plumes

The HOTRAY code is used to evaluate the path integrated gain of electromagnetic ion cyclotron (EMIC) waves as a function of frequency in two propagation bands above the O+ and He+ gyrofrequencies. Calculations are performed over a range of L shell (3 &lt; L &lt; 7) assuming a cold H+‐He+‐O+ plasma with an additional bi‐Maxwellian hot ring current proton distribution. The cold plasma model includes a plasmasphere and high‐density storm time plume region containing spatial density fluctuations. The strongest wave gain (&gt;40 dB) is found near the plasmapause, within regions with density structure in the plume, and in the low‐density trough at L ≥ 6.5. As a self‐consistent test on whether EMIC waves play an important role in relativistic electron loss from the radiation belts, the minimum cyclotron resonant electron energy is evaluated as a function of wave frequency and L shell for those EMIC waves that exhibit significant gain. The lowest electron resonant energies (approximately a few MeV) are found in structured plumes. The sensitivities of both the wave gain and electron minimum resonant energy to variation in thermal ion compositions, the energetic proton properties, or plume density structure are also investigated.

Proton beam velocity distributions in an interplanetary coronal mass ejection

Abstract. The plasma and magnetic-field instruments on the Helios 2 spacecraft, which was on 3 April 1979 located at 0.68 AU, detected an interplanetary coronal mass ejection (ICME) that revealed itself by the typical signature of magnetic field rotation. The solar wind flow speed ranged between 400 and 500 km/s. We present here some detailed proton velocity distributions measured within the ICME. These cold distributions are characterized by an isotropic core part with a low temperature, T≤105 K, but sometimes reveal a broad and extended hot proton tail or beam propagating along the local magnetic field direction. These beams lasted only for about an hour and were unusual as compared with the normal ICME protons distribution which were comparatively isotropic. Furthermore, we looked into the velocity and field fluctuations in this ICME and found signatures of Alfvén waves, which might be related to the occurrence of the hot proton beams. However, it cannot be excluded that the beam originated from the Sun.

Spatial Structure and Collisionless Electron Heating in Balmer‐dominated Shocks

Balmer-dominated shocks in supernova remnants (SNRs) produce strong hydrogen lines with a two-component profile composed of a narrow contribution from cold upstream hydrogen atoms and abroad contribution from hydrogen atoms that have undergone charge transfer reactions with hot protons. Observations of emission lines from edgewise shocks in SNRs can constrain the gas velocity and collisionless electron heating at the shock front. Downstream hydrogen atoms engage in charge transfer, excitation, and ionization reactions, defining an interaction region called the shock transition zone. The properties of hot hydrogen atoms produced by charge transfers (called broad neutrals) are critical for accurately calculating the structure and radiation from the shock transition zone. This paper is the third in a series describing the kinetic, fluid, and emission properties of Balmer-dominated shocks, and it is the first to properly treat the effect of broad neutral kinetics on the shock transition zone structure. We use our models to extract shock parameters from observations of Balmer-dominated SNRs. We find that the inferred shock velocities and electrontemperaturesarelower thanthoseof previouscalculations by 1500 km s � 1 . This effect is primarily due to the fact that excitation by proton collisions and charge transfer to excitedlevelsfavorthehigh-speedpartof theneutralhydrogenvelocitydistribution.Ourresultshaveastrongdependence on the ratio of the electron to proton temperatures, � � Te/Tp, which allows us to construct a relation � (vs) between the temperature ratio and the shock velocity.We compare our calculations to previous results byGhavamian and coworkers. Subject headingg shock waves — supernova remnants Online material: color figures

Ultra‐low‐frequency waves and associated wave vectors observed in the plasma sheet boundary layer by Cluster

Waves in the Pc1–Pc2 frequency range (0.1–5 Hz) are studied using Cluster magnetic field data. In the plasma sheet boundary layer, Cluster observed harmonically related waves with the fundamental near the local proton cyclotron frequency (Ωp). These waves had components both parallel and perpendicular to the local magnetic field (B0). Application of the wave telescope yielded the full wave vector (k) of the waves and showed that they propagated nearly perpendicular to B0. Associated with the waves were two counterstreaming ion beams with a relative velocity of approximately 4000 km/s. During wave activity, the tailward streaming beam increased in energy flux, and subsequently, energy flux increased in directions perpendicular to B0. We suggest two possible sources for the waves: inverse Landau resonance with an accelerated electron beam and an electromagnetic ion/ion cyclotron instability. The change in the ion distribution suggests these waves could contribute to the formation of the hot protons of the central plasma sheet.

The synchrotron boiler and the spectral states of black hole binaries

We study the effects of synchrotron self-absorption on the Comptonising electron distribution in the magnetised corona of accreting black holes. We solve the kinetic equations assuming that power is supplied to the coronal electrons through Coulomb collisions with a population of hot protons and/or through the injection of non-thermal energetic electrons by some unspecified acceleration process. We compute numerically the steady state particle distributions and escaping photon spectra. These numerical simulations confirm that synchrotron self-absorption, together with e-e Coulomb collisions, constitute an efficient thermalising mechanism for the coronal electrons. When compared to the data, they allow us to constrain the magnetic field and temperature of the hot protons in the corona independently of any dynamical accretion flow model or geometry. A preliminary comparison with the Low Hard State (LHS) spectrum of Cygnus X-1 indicates a magnetic field below equipartition with radiation, suggesting that the corona is not powered through magnetic field dissipation (as assumed in most accretion disc corona models). However, in the LHS of Cygnus X-1 and other sources, our results also point toward proton temperatures substantially lower than what predicted by the ADAF-like models. In contrast, in the High Soft State (HSS) both the proton temperature and magnetic field could be much higher. We also show that in both spectral states the magnetised corona could be powered essentially through acceleration of non-thermal particles. The main differences between the LHS and HSS coronal emission can then be understood as the consequence of the much stronger radiative cooling in the HSS caused by the soft thermal radiation coming from the geometrically thin accretion disc.

Electrostatic instabilities triggered by finite amplitude Alfvén/ion‐cyclotron waves and relative drifts among the ion components in the magnetosphere

Alfvén/ion‐cyclotron waves have been observed in several regions of the magnetosphere. Parametric decays of finite amplitude Alfvén/ion‐cyclotron waves in the presence of He+ ions and a mixed population of thermal and hot protons have been shown to lead to several parametric instabilities. These studies assumed that heavy ions are not drifting relative to each other. However, a relative drift velocity among the ions can affect known parametric decays and can also lead to new ones. Moreover, finite amplitude waves in a plasma system with drifting ion species are shown to destabilize nonlinear ion‐acoustic‐like waves supported by each species. Finally, linear ion‐acoustic waves supported by different ion species can also be destabilized because of the relative drift between ion components.