Cold Protons Research Articles

Electromagnetic ion cyclotron waves instability threshold condition of suprathermal protons by kappa distribution

The well‐known generalized Lorentzian (kappa) distribution generally provides a good representation for the high‐energy tail population of natural cosmic suprathermal plasmas. In this study we examine the electromagnetic ion cyclotron waves (EMIC) instability driven by the temperature anisotropy condition (T⊥/T∥ > 1) of suprathermal protons modeled with a typical kappa distribution in a cold multispecies plasma (electron, H+, He+, and O+). Since the EMIC wave instability is found to be significant typically above the O+ band, we apply a linear theory to study the instability threshold condition for the He+ and H+ bands particularly around the geostationary orbit. The instability threshold condition, as in the case for a regular bi‐Maxwellian, is found to follow a typical form T⊥/T∥ − 1 = S/β∥α, with higher values in the He+ band than those in the H+ band in the case of the strong wave instability owing to a lower maximum wave growth in the He+ band. As the spectral index κ increases, the instability threshold condition generally decreases and tends to the lowest limiting values of the bi‐Maxwellian, since the evaluation by the bi‐Maxwellian generally overestimates the maximum wave growth. The densities of the cold components (particularly protons) have impacts on the threshold condition primarily in the H+ band, with a higher density of cold protons leading to a lower value of the threshold condition. The results above may further reveal the nature of this instability threshold condition for the EMIC waves in any other space plasmas where an anisotropic suprathermal ion component and cold multicomponents are present together.

Temperature anisotropies of electrons and two-component protons in the dusk plasma sheet

Abstract. To investigate the cold plasma sheet formation under northward IMF, we study the temperature anisotropies of electrons and two-component protons observed by the Geotail spacecraft. The two-component protons, which are occasionally observed in the dusk plasma sheet near the low-latitude boundary, are the result of spatial mixing of the hot protons of the magnetosphere proper and the cold protons from the solar wind. Recent research focusing on the two-component protons reported that the cold proton component at times has a strong anisotropy, and that the sense of the anisotropy depends on the observed locations. Since electrons have been known to possess a strong parallel anisotropy around the low-latitude boundary layer, we compare anisotropies of electrons and protons to find that the strengths of parallel anisotropies of electrons and the cold proton component are in good correlation in the tail flank. The parallel anisotropy of electrons is stronger than that of the cold proton component, which is attributed to selective heating of electrons. We further find that the strengths of the parallel anisotropies in the tail flank depend on the latitudinal angle of the IMF; strong parallel anisotropies occur under strongly northward IMF. We discuss that the Kelvin-Helmholtz vortices, which developed under strongly northward IMF, and the resultant magnetic reconnection therein may lead to the strong parallel anisotropies observed in the tail flank.

The Particle Content of Extragalactic Jets

Recent radio and X-ray data from radio sources in galaxy clusters are used to place constraints on the particle content and kinematics of jets that supply these radio sources. These data show that the pdV work required to inflate the radio lobes in the ICM exceeds all other estimates of the amount of energy needed to supply the observed radio emission. If the required jet energy density has an isotropic pressure, then in almost all cases the jets cannot be confined by the external pressure of the ICM. This problem can be resolved with jets dominated by a cold and relatively dense proton population, but even here the accompanying energy density in electrons alone can cause jet decollimation in many cases. Calculation of particle interactions in a cold proton jet shows the electron-proton energy transfer times to be very long. Electron-positron jets, unless highly beamed and with an unusual energy distribution, cannot solve the decollimation problem. A viable alternative may be Poynting flux-dominated jets with a very low particle content.

A broadband leptonic model for gamma-ray emitting microquasars

Observational and theoretical studies point to microquasars (MQs) as possible counterparts of a significant fraction of the unidentified gamma-ray sources detected so far. At present, a proper scenario to explain the emission beyond soft X-rays from these objects is not known, nor what the precise connection is between the radio and the high-energy radiation. We develop a new model where the MQ jet is dynamically dominated by cold protons and radiatively dominated by relativistic leptons. The matter content and power of the jet are both related with the accretion process. The magnetic field is assumed to be close to equipartition, although it is attached to and dominated by the jet matter. For the relativistic particles in the jet, their maximum energy depends on both the acceleration efficiency and the energy losses. The model takes into account the interaction of the relativistic jet particles with the magnetic field and all the photon and matter fields. Such interaction produces significant amounts of radiation from radio to very high energies through synchrotron, relativistic Bremsstrahlung, and inverse Compton (IC) processes. Variability of the emission produced by changes in the accretion process (e.g. via orbital eccentricity) is also expected. The effects of the gamma-ray absorption by the external photon fields on the gamma-ray spectrum have been taken into account, revealing clear spectral features that might be observed. This model is consistent to the accretion scenario, energy conservation laws, and current observational knowledge, and can provide deeper physical information of the source when tested against multiwavelength data.

Hadronic High‐Energy Gamma‐Ray Emission from the Microquasar LS I +61 303

We present a hadronic model for gamma-ray production in the microquasar LS I $+61 303$. The system is formed by a neutron star that accretes matter from the dense and slow equatorial wind of the Be primary star. We calculate the gamma-ray emission originated in $pp$ interactions between relativistic protons in the jet and cold protons from the wind. After taking into account opacity effects on the gamma-rays introduced by the different photons fields, we present high-energy spectral predictions that can be tested with the new generation Cherenkov telescope MAGIC.

Particle Simulation of an Ultrarelativistic Two-Stream Instability

A two-stream instability in an unmagnetized plasma is examined by a particle-in-cell simulation. Each beam initially consists of cold electrons and protons that stream at a relative Lorentz factor 100. This is representative for plasma close to the external shocks of gamma-ray bursts. An electrostatic wave develops which saturates by trapping electrons. This wave collapses and the resulting electrostatic turbulence gives an electron momentum distribution that resembles a power law with a spectral break. Some electrons reach Lorentz factors over 1000.

Case studies of the dynamics of ionospheric ions in the Earth's magnetotail

This paper presents case studies of the dynamics of the terrestrial ions in the midplasma sheet and inside the lobes (∼17–19 RE). The high time resolution measurements of H+, He+, and O+ ions made on board Cluster show that these ions are massively injected into the tail during substorms/storms from the nightside ionosphere and mainly dispersed by time of flight effects; a single oxygen injection being able to account for over 80% of the oxygen population of the midtail plasma sheet during storm time. Inside the lobes, during disturbed times, ionospheric oxygen ions appear as nearly monoenergetic beams, quasi field‐aligned, propagating antisunward from the ionosphere, as expected from the “cleft ion fountain.” Most of the time, the ionospheric protons are very cold and their distribution function is not fully measurable by a charged spacecraft. However, we show that protons can, at times, acquire a large drift motion, reach energy larger than 30 eV, and be directly measurable by the CIS spectrometers. This occurs when large disturbances propagate in the plasma sheet boundary layer during both quiet and disturbed periods. We show that the large, variable, Alfvén waves generated by these plasma sheet disturbances modulate the energy of lobe protons and oxygen ions and inject electromagnetic energy, in excess of 15 × 10−3 W/m2, down to the polar cap. Deeper inside the plasma sheet boundary layer, large electric fields associated with the Earthward stream of plasma sheet particles give enough drift energy to a very cold ionospheric proton population to become fully detectable by the Cluster ion spectrometers.

Neutrinos from pulsar wind bubbles as precursors to gamma-ray bursts.

The supranova model for gamma-ray bursts (GRBs) has recently gained popularity. In this scenario the GRB occurs weeks to years after a supernova explosion, and is located inside a pulsar wind bubble (PWB). High energy protons from the PWB can interact with photons from the rich radiation field inside the PWB or collide with cold protons from the supernova remnant, producing pions which decay into approximately 10-10(3) TeV neutrinos. The predicted neutrino flux from the PWBs that host the GRBs should be easily detectable by planned 1 km(2) detectors.

Dynamics of Temperature and Density of Cold Protons of the Earth's Plasmasphere Measured by the Auroral Probe/Alpha-3 Experiment Data during Geomagnetic Disturbances

We present the results of temperature and density measurement of plasmaspheric protons under quiet and disturbed conditions in the night and dayside sectors of the plasmasphere obtained with the Auroral Probe/Alpha-3 instrument during September 1996 and January 1997. According to the experimental data, the proton temperature in the night sector of the plasmasphere depends on the level of geomagnetic disturbance: it is found that at night hours the values of temperatures inside the plasmasphere at 2.4 < L < 3.5 decreased considerably after the commencement of a geomagnetic storm. The temperature decrease, as a rule, was accompanied by the formation of a flat plateau on the density distribution n(L) at 2.4 < L < 3.5. The above experimental facts (decreasing proton temperature and formation of a flat part on the n(L) distribution) allow us to conclude that the decrease in the proton temperature in the night sector of the plasmasphere connected with magnetic disturbances is caused by the filling of field tubes (depleted after the commencement of the storm) with colder ionospheric plasma. The proton temperature in the dayside sector of the plasmasphere virtually does not depend on the level of the geomagnetic disturbance.

Cosmic rays from microquasars: A narrow component to the CR spectrum?

We propose that relativistic Galactic jets like those observed in GRS 1915+105 and GRO J1655-40 may produce a small but measurable contribution to the cosmic ray (CR) spectrum. If these jets contain cold protons and heavy ions (as in the case of SS433), it is plausible that this component will consist of a narrow spectral feature, with a mean particle energy corresponding roughly to the bulk kinetic particle energy in the beam, . Based on the current estimates of , this feature will fall into the range of 3–10 GeV. The presence of several sources with different will lead to the superposition of several such peaks. In addition to the narrow peaks, diffusive particle acceleration should also produce a powerlaw, whose low energy cutoff at or above would be visible as an additional spectral feature. The large metallicities measured in several binary companions of jet sources suggest that this CR component could have an anomalous composition compared to the bulk Galactic CR spectrum. We provide estimates of the effects of adiabatic losses which are the greatest challenge to models of narrow band CR production in microquasar jets. While the total energy contained in the microquasar CR component is highly uncertain, the local CR spectrum in the vicinity of any microquasar should be severely affected. The upcoming AMS 02 experiment will be able probe the low energy CR spectrum for such components and for composition anomalies. The spectrally peculiar gamma-ray emission produced by interaction of the ISM with CRs surrounding microquasars might be detectable by GLAST. If the presence of a microquasar CR proton component can be ruled out observationally, this argument could be turned around in favor of electron-positron jets. We show that existing OSSE/GRO and future INTEGRAL data on the Galactic 511 keV line flux put interesting constraints on the particle content of microquasar jets. The process of CR production in relativistic flows inside the Galaxy is fundamentally different from the standard picture of CR production in nonrelativistic shocks in supernova remnants, because the particles injected by a relativistic flow are already relativistic, without any need for diffusive acceleration.

The magnetosheaths of the outer planets

This paper provides a review of past work on the magnetosheaths of the outer planets and also provides the most complete look to date at the plasma parameters in these magnetosheaths. We find that proton distributions in the magnetosheaths of Jupiter, Saturn, and Neptune (but not Uranus) are well represented by two Maxwellians with the same velocity but different temperatures. The hot proton component comprises about 40% of the total density and has a temperature about six times that of the cold protons. The Jovian magnetosheath shows significant motion, with sunward flow not uncommon when the magnetosheath region moves outwards, probably due to changes in solar wind pressure. Gas dynamic models of the boundaries show that the magnetospheres of Jupiter and Saturn are flattened at the poles. Deviations from the predictions of gas dynamics are observed, both because of time-dependent effects and systematic effects such as encounters with the plasma depletion layer and plasma mantle, both of which are MHD effects. Mirror mode waves are ubiquitous in the magnetosheaths, but other waves and oscillations are also observed, including one so far unique to Uranus which may occur downstream of parallel shocks.

The ion-acoustic soliton: A gas-dynamic viewpoint

The properties of fully nonlinear ion-acoustic solitons are investigated by interpreting conservation of total momentum as the structure equation for the proton flow in the wave. In most studies momentum conservation is regarded as the first integral of the Poisson equation for the electric potential and is interpreted as being analogous to a particle moving in a pseudo-potential well. By adopting an essentially gas-dynamic viewpoint, which emphasizes momentum conservation and the properties of the Bernoulli-type energy equations, the crucial role played by the proton sonic point becomes apparent. The relationship (implied by energy conservation) between the electron and proton speeds in the transition yields a locus—the hodograph of the system–which shows that, in the first half of the soliton, the electrons initially lag behind the protons until the charge neutral point is reached, after which they run ahead of the protons. The system reaches an equilibrium point (the center of the soliton) before the proton flow goes sonic. It follows that the critical ion-acoustic Mach number, Mc, above which smooth, continuous solitons cannot be constructed, stems from the requirement that the two equilibrium points of the structure equation coalesce at the proton sonic point of the flow. In general the range of the ion-acoustic Mach numbers, Mep, in which solitons exist, is extended beyond the classical range 1&amp;lt;Mep&amp;lt;1.6. In the special case of cold protons and hot electrons with an adiabatic index 2, the structure equation may be integrated in closed form. This analytic solution describes the fully nonlinear counterpart to the sech2 shaped pulses characteristic of weakly nonlinear waves and shows that solitons exist only if 1&amp;lt;Mep&amp;lt;2. The corresponding maximum potential, associated with the critical ion-acoustic Mach number, can be between 1.3kTe and 10kTe depending upon the values of the adiabatic indices of the electrons and protons and the proton Mach number.

MERLIN observations of relativistic ejections from GRS 1915+105

We present high resolution MERLIN radio images of multiple relativistic ejections from GRS 1915+105 in 1997 October / November. The observations were made at a time of complex radio behaviour, corresponding to multiple optically-thin outbursts and several days of rapid radio flux oscillations. The radio imaging resolved four major ejection events from the system. As previously reported from earlier VLA observations of the source, we observe apparent superluminal motions resulting from intrinsically relativistic motions of the ejecta. However, our measured proper motions are significantly greater than those observed on larger angular scales with the VLA. Under the assumption of an intrinsically symmetric ejection, we can place an upper limit on the distance to GRS 1915+105 of 11.2 +/- 0.8 kpc. Solutions for the velocities unambiguously require a higher intrinsic speed by about 0.1c than that derived from the earlier VLA observations, whilst the angle to the line-of-sight is not found to be significantly different. At a distance of 11 kpc, we obtain solutions of v = 0.98 (-0.05,+0.02)c and theta = 66 +/- 2 degrees. The jet also appears to be curved on a scale which corresponds to a period of around 7 days. We observe significant evolution of the linear polarisation of the approaching component, with large rotations in position angle and a general decrease in fractional polarisation. The power input into the formation of the jet is very large, >10^38 erg/s at 11 kpc for a pair plasma. If the plasma contains a cold proton for each electron, then the mass outflow rate, >10^18 g/sec is comparable to inflow rates previously derived from X-ray spectral fits.

The L mode in electromagnetic proton-cyclotron waves in plasmas modelled by a Lorentzian distribution function

The L mode in electromagnetic proton-cyclotron waves (EPCWs) propagating parallel to a uniform ambient magnetic field is studied here analytically. A generalized Lorentzian distribution function is used to model the plasma. Analytical expressions for the wavenumber and for both the temporal and convective growth rates for a multi-ion plasma are obtained within the linear theory. This analytical approach is appropiate for β∥&lt;1, which is the ratio of plasma kinetic pressure to magnetic field pressure. The characteristics of the unstable spectrum are found to be independent of high-energy particles. For a plasma composed of electrons plus hot and cold protons, it is shown that the maximum growth rates as functions of cold-proton concentration δ can always decrease, or can increase until δ reaches a certain peak value and decrease thereafter, or can always increase, depending on the thermal anisotropy of the hot protons. This behaviour is similar to that in Maxwellian plasmas. However, for the convective growth rate, the expression for the optimum cold-proton concentration shows a significant dependence on the spectral index κ. Therefore, when cold protons are injected, it is more difficult to obtain optimum amplification in a Lorentzian plasma than in a Maxwellian plasma. It is also shown that the influence of the high-energy tail on the generation and amplification processes of the EPCWs is controlled by thermal anisotropy and cold-ion population. As a consequence of the latter, temporal and convective growth rates can be larger than, equal to or smaller than those of Maxwellian plasmas, depending on the anisotropy of the hot-proton distribution and on the cold-proton concentration.

Comparing the antiproton and proton and progress toward cold antihydrogen

The most stringent test of CPT invariance with a baryon system is a 1 part in 10 9 comparison of the charge-to-mass ratios of the antiproton and proton. An improved Q/M comparison for antiproton and protons at the 10 −10 level of accuracy is underway, utilizing an antiproton and an H − ion confined at the same time in a Penning trap. Precise spectroscopic comparisons of cold antihydrogen and hydrogen atoms should produce much more accurate CPT tests. The recent experimental progress toward cold antihydrogen includes the accumulation of more than a million 4.2 K positrons in ultrahigh vacuum, and a demonstrated low temperature interaction of cold electrons and protons in a nested Penning trap. The first attempt at producing cold antihydrogen is scheduled for late 1996. Collaborations and facilities for antihydrogen studies after 1996 will be mentioned.

GEOTAIL observation of ring‐shaped ion distribution functions in the plasma sheet‐lobe boundary

The ring‐shaped velocity distribution of ions with energies of a few keV of the gyrating motion has at times been detected in the boundary region between the plasma sheet and the lobe in the distant tail at XGSM ∼ −70 and −170Re. The normal direction of the ring‐shaped distribution is almost parallel to the magnetic field, and the distribution moves tailward. In many cases the fast flowing ions of the Plasma Sheet Boundary Layer (PSBL) are observed simultaneously. The density of the ring is comparable to the density of the cold ion stream observed in the lobe. We discuss the possibility that these ring ions are generated from cold proton streams by the thermoelectric field that exists at the plasma sheet‐lobe boundary.

Comparative study of the effect of cold ions and thermal anisotropy on the convective electromagnetic proton cyclotron instability

Although the role played by cold ions on the electromagnetic proton-cyclotron instability has been thoroughly investigated, there are some aspects which deserve further attention. Moreover, since the presence of ion cyclotron waves in the magnetosphere has been experimentally established it is important to have a full understanding of the role played by cold ions. Thus, it is shown here that the main effect of cold ions on the proton-cyclotron instability is to shift the unstable spectrum. If the only cold species are protons, then the shift of the spectrum is always towards lower frequency values, i.e. away from the marginal mode. If in the absence of cold protons the maximum convective growth rate lies far from the marginal mode, the only effect of cold protons is to shift the spectrum further away from the marginal mode. However, if the maximum convective growth rate in the absence of cold protons lies close to the marginal mode, then the shift of the spectrum leads also to a large amplification. The reason for this behaviour lies in the fact that as the thermal anisotropy decreases, the frequency range of the unstable spectrum also decreases, stabilizing high frequency waves. Since unstable higher frequency waves occur in the absence of cold protons, these are the first to be stabilized. The observed amplification due to cold protons is the result of comparing waves which have suffered some stabilization with waves which, due to the shift of the unstable spectrum, have not yet been affected by the stabilization which follows the reduction of the thermal anisotropy. A consequence of these results is that, since the thermal anisotropy decreases as the instability develops, the instability lasts longer in the presence of cold protons than in their absence. If more than one cold species are present, the situation is more complex but the basic mechanism is the same. It is conjectured that the catalytic role played by cold He + ions in the generation of ion cyclotron waves in the magnetosphere consists of shifting the unstable spectrum away from a forbidden or sta- bilization region.

Pitch angle properties of magnetospheric thermal protons and satellite sheath interference in their observation

Cold proton observations from the geosynchronous GEOS 2 satellite are presented to show the pitch angle distribution of the refilling cold ion population found beyond the plasmapause. This refilling cold ion population flows into the depleted equatorial regions of the flux tubes from the topside ionosphere. This refilling is observed both day and night. The ions have energies between 0.5 and 3 eV. These energy characteristics are consistent with other recent observations. Although the observed angular distribution of these ions is highly complex, when allowance is made for the satellite sheath several conclusions can be made concerning the ion pitch angle distribution. The angular distribution is very field aligned with a characteristic source cone angle ranging from 10° to 20°. This range of angles is consistent with ions originating below 20,000 km in the exosphere rather than in the heavy‐ion ionosphere. As the flux tube density increases, the degree of field alignment decreases; however, based on the limited pitch angle coverage it is not possible to determine if the field‐aligned component is simply being swamped by the local isotropic component or if the field‐aligned component changes its pitch angle characteristics. A crucial aspect of the study was the availability of a unique data base of sheath‐plasma observations. The observations were obtained by using the boom mounting and voltage biasing capabilities of the detector package in relation to the satellite. These data enabled us to describe how the satellite sheath affects the observation of cold (&lt;5 eV) protons. This qualitative understanding enabled the highly anisotropic data to be interpreted in terms of magnetospheric pitch angle distributions. The overall implications of this sheath‐plasma coupling is that a technique to make satellite sheath observations has been demonstrated.

Thermal protons in the morning magnetosphere: Filling and heating near the equatorial plasmapause

Thermal H + distributions have been measured as the European Space Agency GEOS-1 satellite passed through the late morning equatorial magnetosphere, plasmapause and plasmasphere. The unique capabilities of the on-board Supralhermal Plasma Analysers (SPA) have been used to overcome the retarding floating potential of the satellite and measure the velocity distribution of the cold protons. In the magnetosphere an enhanced source cone of such ions with a temperature of ~ 0.5 eV is a signature of the filling process occurring outside the plasmapause where flux tubes are relatively empty. In the plasmasphere the thermal H + is essentially isotropic with a temperature less than 0.5 eV but the motion of the satellite introduces apparent drift. These measurements of cold proton velocity distribution now permit a reappraisal of the definition of the “plasmapause”. It becomes inappropriate to use an arbitrary empirical density, e.g. the conventional 10 cm −3, in order to establish a boundary. It is now possible to identify a plasmapause interaction region where the two cold proton populations co-exist. This region generally lies Earthward of the 10 cm −3 density level, has a width which is strongly dependent on magnetic activity and the temperature is typically between 0.5 and 1.5 eV. The change from “filled” to “unfilled” flux tubes relates to the physical processes which are occurring and the controlling electric field configuration; in particular, the last closed equipotential. Throughout this region, in going from the plasmasphere to the magnetosphere, the plasma drift motion is expected to change from corotation to a convection which is controlled by E × B, and is predominantly Sunward due to the dawn-dusk electric field. Crossing the plasmapause on the morning side, little change in drift direction should occur but subtle variations in the ionic velocity distribution do reflect the change in the degree of flux tube density equilibrium. Our first direct measurement of the magnetospheric E × B drift has been reported previously but here measurements from a selected six day period show how the plasma in the plasmapause region responds to changing magnetospheric activity. The drift velocities cannot he derived with high accuracy but the analysis shows that the technique can provide a valid mapping of the magnelospheric electric field. In addition, since the magnetospheric cold plasma distribution is observed after it has come from the ionosphere, a distance of many Earth radii, the scattering and accelerating mechanisms along the flux tube can be studied. For this particular data-set taken in the late morning, the maximum potential drops along the flux tubes were less than a volt. The ionospheric proton source cone is observed to be broad, pitch angle scattering persists up to 40 or even 70°. Although these results throw new light on the plasmaspheric filling process one must recognise that, however the plasmapause is defined, it is not a simple matter to map this boundary from the equatorial plane down to low altitudes and the mid-latitude trough.

The lower hybrid density drift instability with cold plasma

The linear Vlasov dispersion relation for the lower hybrid density drift instability is studied in a four component (hot electrons and protons, cold electrons and protons) plasma. The introduction of a cold ion population monotonically reduces the maximum growth rate of the instability. Reduction of Tc/Th, the ratio of temperatures of the cold and hot plasmas, reduces both the real frequency and the growth rate of the instability. Near Tc/Th=10−2 a higher frequency branch of this instability emerges and for fixed nc/nh exhibits an increasing maximum growth rate as Tc/Th decreases further. The ratio Tc/Th for the ions is the crucial parameter and deserves detailed magnetospheric studies.