Inner radiation belt source of helium and heavy hydrogen isotopes

Nuclear interactions between inner zone protons and atoms in the upper atmosphere provide the main source of energetic H and He isotopes nuclei in the radiation belt. This paper reports on the specified calculations of these isotope intensities using various inner zone proton intensity models (AP-8 and SAMPEX/PET PSB97), the atmosphere drift-averaged composition and density model MSIS-90, and cross-sections of the interaction processes from the GNASH nuclear model code. To calculate drift-averaged densities and energy losses of secondaries, the particles were tracked in the geomagnetic field (modelled through IGRF-95) by integrating numerically the equation of the motion. The calculations take into account the kinematics of nuclear interactions along the whole trajectory of trapped proton. The comparison with new data obtained from the experiments on board RESURS-04 and MITA satellites and with data from SAMPEX and CRRES satellites taken during different phases of solar activity shows that the upper atmosphere is a sufficient source for inner zone helium and heavy hydrogen isotopes. The calculation results are energy spectra and angular distributions of light nuclear isotopes in the inner radiation belt that may be used to develop helium inner radiation belt model and to evaluate their contribution to SEU (single event upset) rates.     

The optical to X-ray spectrum of the broad-line ultrasoft AGN RE J2248-511

We present a series of monitoring observations of the ultrasoft broad-line Seyfert galaxy RE J2248-511 with XMM-Newton. Previous X-ray observations showed a transition from a very soft state to a harder state five years later. We find that the ultrasoft X-ray excess has re-emerged, yet there is no change in the hard power-law. Reflection models with a reflection fraction of 15, and Comptonisation models with two components of different temperatures and optical depths (kT₁ = 83 keV, T₁ = 30 eV, τ₁ = 0.8; KT₂ = 3.5 keV, T₂ = 60 eV, τ₂ = 2.8) can be fit to the spectrum, but cannot be constrained. The best representation of the spectrum is a model consisting of two blackbodies (kT₁ = 0.09 ± 0.01 keV, kT₂ = 0.21 ± 0.03 keV) plus a power-law (Γ = 1.8 ± 0.08). We also present simultaneous optical and infrared data showing that the optical spectral slope also changes dramatically on timescales of years. If the optical to X-ray flux comes primarily from a Comptonised accretion disk we obtain estimates for the black hole mass , accretion rate and inclination cos(i)  0.8 of the disk.     

Solar cycle variation of the low-altitude trapped proton flux

Under NASA's Space Environment Effects (SEE) program, we are developing new models for the low-altitude (250–1000 km, L < 1.5) trapped radiation environment based on data from the TIROS/NOAA polar orbiting spacecraft. The unique features of this data base and model include the long time series (more than one complete solar cycle) obtained from the TIROS/NOAA data and the use of a coordinate system more applicable to the low-altitude environment. The data show a strong variation (as much as a factor of 10) over the solar cycle and a hysteresis effect between the rising and falling portions of the solar cycle. Both the solar cycle variation and the hysteresis are functions of L. In addition to the hysteresis effect, the flux during a given cycle appears to be a function of the previous cycle. Superimposed on the gradual variation over the solar cycle, transient effects, correlated with solar particle events (SPEs), can be clearly seen. Comparison with the AP8 models shows that the measured flux is a factor of 2–3 higher than the model. These data have important implications for the development and use of trapped radiation models, and will also contribute to our knowledge of the source and loss mechanisms at work in the inner zone.     

Fe XVII X-ray lines in solar coronal plasmas

Calculated intensities of the Fe X-ray lines due to transitions 2p⁶ − 2p⁵3d lines (near 15 Å) and 2p⁶ − 2p⁵3s lines (near 17 Å) are compared with measured line intensities in solar and tokamak spectra. For the solar spectra, temperature T_e is obtained from the ratio of the Fe 16.776 Å line to a nearby Fe line. We find excellent agreement for all the major Fe line features in the 15–17 Å region except the Fe 15.015 Å line, the observed flux of which is less than the theoretical by a factor f. We find that f strongly depends on the heliocentric angle θ of the emitting region, being smallest (0.2) when the region is nearest Sun centre, but nearly 1 near the limb. Attributing this to resonance scattering, we are able to deduce the path length and electron density from the observations. Possible application to stellar active regions is given.     

Study of correlations between waves and particle fluxes measured on board the DEMETER satellite

The topic of relativistic electron dynamics in the outer radiation belt has received considerable attention for many years. Nevertheless, the problem of understanding the physical phenomenon involved is far from being resolved. In this paper, we use DEMETER observations to examine the variations of the energetic electron fluxes and ELF/VLF wave intensities in the inner magnetosphere during the intense 8 November 2004 magnetic storm. Electron flux spectra and associated wave intensity spectra are analysed throughout the magnetic storm and common characteristics or differences to other storm events are retained. The overall objective of this study is to identify and derive parameters that are relevant for particle flux modelling; the time constant characterizing the persistent decay after particle enhancement was found to be one of these important model parameters.The analysis of the 8 November 2004 event reveals that for L-shell parameter higher than 4, an electron flux dropout is observed during the storm’s main phase for electrons in the energy range 0.1–1 MeV, as has been reported from other measurements. Characteristic wave spectra accompanying this phase are analysed. They show a typical enhancement in the frequency range 0.3–10 kHz at onset for all L-shell values under consideration (2 < L < 5). During the first stage of the recovery phase, the electron fluxes are increased to a level higher than the pre-storm level, whereas the level of wave intensity in the frequency range observed below 300 Hz is at its highest. In the second stage, the particle flux decrease goes hand in hand with a global wave activity decline, the relaxation time of the latter being smaller than the former’s one. In some other cases, long-lasting electron enhancement associated with constant wave activity has been observed during this latter stage. For the above mentioned storm, while at low L values the decay time constants are higher for low energy electrons than for high energy electrons, this order is reversed at high L values. At about L = 3.6 the time constant is independent of electron energy.     

Energetic particle environment in near-Earth orbit.

The hazard of exposure to high doses of ionizing radiation is one of the primary concerns of extended manned space missions and a continuous threat for the numerous spacecraft in operation today. In the near-Earth environment the main sources of radiation are solar energetic particles (SEP), galactic cosmic rays (GCR), and geomagnetically trapped particles, predominantly protons and electrons. The intensity of the SEP and GCR source depends primarily on the phase of the solar cycle. Due to the shielding effect of the Earth's magnetic field, the observed intensity of SEP and GCR particles in a near-Earth orbit will also depend on the orbital parameters altitude and inclination. The magnetospheric source strength depends also on these orbital parameters because they determine the frequency and location of radiation belt passes. In this paper an overview of the various sources of radiation in the near-Earth orbit will be given and first results obtained with the Solar, Anomalous, and Magnetospheric Particle Explorer (SAMPEX) will be discussed. SAMPEX was launched on 3 July 1992 into a near polar (inclination 82 degrees) low altitude (510 x 675 km) orbit. The SAMPEX payload contains four separate instruments of high sensitivity covering the energy range 0.5 to several hundred MeV/nucleon for ions and 0.4 to 30 MeV for electrons. This low altitude polar orbit with zenith-oriented instrumentation provides a new opportunity for a systematic study of the near-Earth energetic particle environment.     

基于SAMPEX卫星观测的南大西洋异常区高能质子动态分布特征

利用SAMPEX卫星1992年7月至2004年6月19～27MeV高能质子数据对南大西洋异常区的分布特征进行研究, 发现南大西洋异常区高能质子分布随高度及F_10.7的变化十分显著. 在540±25km高度上, 地磁较为平静时期南大西洋异常区高能质子微分通量随着F_10.7的增大而减小, 同时在F_10.7≥115sfu时减小趋势较为平缓. 对中等及以上磁暴进行统计分析发现, 磁暴期间南大西洋异常区高能质子微分通量和SYM-H指数的绝对值存在明显的反相关关系, 且地磁暴对南大西洋异常区高能质子微分通量存在明显的持续影响效应. 磁暴发生期间高能质子微分通量明显减少. 磁暴恢复相及其之后高能质子微分通量呈现较为显著的恢复过程.      

FEM code simulation of the magnetospheric proton fluxes

We report a study of the numeric solution to the diffusive transport equation for energetic protons magnetically trapped in the Earth's equatorial magnetosphere. The analysis takes into account the pertinent physical processes in this region, including deceleration of protons by Coulomb collisional interactions with free and bound electrons, the charge exchange process, cosmic ray albedo neutron decay source, and electric and magnetic radial diffusion. These results were obtained using the Finite Element Method with magnetic moment and geomagnetic L-shell as free variables. Steady state boundary conditions were imposed at L=1 as zero distribution function and at L=7 with proton distribution function extracted from ATS 6 satellite observations. The FEM-code yields unidirectional proton flux in the energy range of 0.1–1000 MeV at the equatorial top of the geomagnetic lines, and the results are found to be in satisfactorily agreement with the empirical NASA AP-8 model proton flux within the energy range of 0.5–100 MeV. Below 500 keV, the empirical AP-8 model proton fluxes are several orders of magnitude greater than those computed with the FEM-code at L<3. This discrepancy is difficult to explain by uncertainties of boundary spectrum parameters or transport coefficients.     

Statistical properties of SEP event flux declines

The interplanetary space is not a passive medium, which merely constitutes a scene for the propagation of previously accelerated energetic particles, but influences the distribution of particles by changing their energies as well due to interactions with magnetic field inhomogeneities. Such processes manifest themselves in the energy spectra of solar energetic particle (SEP) events. In this paper the fluxes of protons with energies of 4–60 MeV are investigated on the basis of two data sets. Both sets are homogeneous, obtained by the CPME instrument aboard the IMP 8 satellite between 1974 and 2001. The first includes all SEP events where the integral fluxes of >4 MeV protons exceeded 2 particle/cm² s sr. The other set consists of fluxes recorded in differential energy windows between 0.5 and 48 MeV. Important characteristics of SEP events include the rates of decrease of particle flux, which, as well as peak flux time, is an integral feature of the interplanetary medium within a considerable region, surrounding the observation point. The time intervals selected cover the decay phases of SEP events following flares, CMEs and interplanetary shocks of different origin. Only those parts of declines were selected, that could reasonably be described by exponential dependence, irrespective of the gradual/impulsive character of the events. It is shown that the average values of characteristic decay time, τ, and energy spectral index, γ, are all changing with the solar activity phase. Distributions of τ and γ values are obtained in SEPs with and without shocks and during different phases of events: just after peak flux and late after maximum.     

Spatial and temporal variations of energetic trapped helium ions measured with Japanese satellite OHZORA

The results of measurements of absolute flux values and long term temporal evolution of the spatial distribution of trapped He ions in the energy range 1.2 – 9.2 MeV/nucleon below L = 4 are reported. The observations were made with ion counter on board the Japanese OHZORA satellite during the period of January 1984 through March 1987.     

Fluctuation analyses of the X-ray background

We review recent progress in the use of analyses of fluctuations in the cosmic X-ray background (XRB) to determine the source counts below the detection thresholds. Three flux domains are discussed: the range around 10⁻¹²erg cm⁻² s⁻¹ where the Ginga and Einstein Observatory results remain inconsistent unless the sources at these fluxes (mainly Seyfert galaxies) are highly absorbed at low energies, the 10⁻¹⁴erg cm⁻² s⁻¹ zone where the flattening of the source counts predicted by fluctuation analyses of Einstein Observatory images is now confirmed by Rosat, and the 10⁻¹⁵erg cm⁻² s⁻¹ flux domain, where fluctuation analyses of Rosat images show that source counts remain subeuclidean with very little contribution to the XRB coming from these sources.     

Sources of inner radiation zone energetic helium ions: Cross-field transport versus in-situ nuclear reactions

Radial transport theory for inner radiation zone MeV He ions has been extended by combining radial diffusive transport, losses due to Coulomb friction and charge exchange reaction with local generation of ³He and ⁴He ions due to nuclear reactions taking place on the inner edge of the inner radiation zone. From interactions between high energy trapped protons and upper atmospheric constituents we have included a nuclear reaction yield helium flux source that was numerically derived from a nuclear reaction model originally developed at the Institute of Nuclear Researches of Moscow, Russia and implemented in the computer system at the University of Campinas, Brazil. Magnetospheric transport computations have been made covering the L-shell range L=1.0 to 1.6 and the resulting MeV He ion flux distributions show a strong influence of the local nuclear source mechanism on the inner zone energetic He ion content.     

Cyclotron features in X-ray spectra of accreting pulsars

The hard X-ray spectra of small subset of accreting pulsars show absorption-like line features in the range 10–100 keV. These lines, referred to as cyclotron lines or cyclotron resonance scattering features, are due to photons scattered out of the line of sight by electrons trapped in the 10¹² G pulsar polar cap magnetic field. In this paper we present a review of observations, from the discovery of a cyclotron line in Hercules X-1 to recent results with RXTE and INTEGRAL.     

Escaping near-relativistic electron beams from the solar corona

Processes in the solar corona are prodigious accelerators of energetic ions, and electrons. The angular distribution, composition, and spectra of energetic particles observed near Earth gives information on the acceleration mechanisms. A class of energetic particle observations particularly useful in understanding the solar acceleration is the near-relativistic impulsive beam-like electron events. During five years of operation the Advanced Composition Explorer (ACE) has measured well over 400 electron events. Approximately 25% of these electron events are impulsive beam-like events that are released onto interplanetary field lines predominantly from western solar longitudes. We extend our initial 3 year study during the rise to solar maximum (Haggerty and Roelof, 2002; Simnett et al., 2002) to a five year statistical analysis of these beam-like energetic electron events in relationship to optical flares, microwave emission, soft X-ray emission, metric and decametric type-III radio bursts, and coronal mass ejections.     

The detection of energetic cometary and solar particles by the EPONA instrument on the Giotto mission

EPONA is an energetic particle detector system incorporating totally depleted silicon surface barrier layer detectors. Active and passive background shielding will be employed and, by applying various techniques, particles of different species, including electrons, protons, alpha particles and pick-up ions of cometary origin may be detected over a wide spectrum of energies extending from the tens of KeV into the MeV range.

The instrument can operate in two modes namely (a) in a cruise phase or storage mode and (b) in a real time mode. During the real time mode, observations at high spatial (octosectoring) and temporal (0.5s) resolution in the cometary environment permit studies to be made of accelerated particles at the bow shock and/or in the tail of the comet. In conjunction with magnetic field measurements on board Giotto, observations of energetic electrons and their anisotropies can determine whether the magnetic field lines in the cometary tail are open or closed. Further, the absorption of low energy solar particles in the cometary atmosphere can be measured and such data would provide an integral value of the pertaining gas and dust distribution. Solar particle background measurements during encounter may also be used to correct the measurements of other spacecraft borne instruments potentially vulnerable to such radiation.

Solar particle flux measurements, obtained during the cruise phase will, when combined with simultaneous observations made by other spacecraft at different heliographic longitudes, provide information concerning solar particle propagation in the corona and in interplanetary space.     

漂移壳追踪方法与内辐射带的长期变化

地磁场的长期变化发迹辐射带结构,如何在当前年代下恰当地使用ＡＥ－８／ＡＰ－８模型,目前国内外对此问题存在着很大的争议。我们在物理分析的基础上给出了当前年代下使用辐射带模型ＡＰ－８的漂移壳追踪方法ＤＳＴＭ（Ｄｒｉｆｔ Ｓｈｅｌｌ Ｔｒａｃｉｎｇ Ｍｅｔｈｏｄ）。计算结果表明地磁场的长期变化对内辐射带的通量分布有着显著的影响。３０－４０年来,南大西洋通量异常区中心向丁和向北发生偏移,高粒子辐射区域的范     

Modeling solar proton access to geostationary spacecraft with geomagnetic cutoffs

Solar energetic particle (SEP) cutoffs at geosynchronous orbit are sensitive to moderate geomagnetic activity and undergo daily variations due to the day–night asymmetry of the magnetosphere. At geosynchronous orbit, cutoff rigidity also has a large directional dependence, with the highest cutoff rigidity corresponding to ions arriving from magnetic east and lowest cutoff rigidity corresponding to ions incident from the west. Consequently, during geomagnetically quiet periods, the SEP flux observed by an eastward facing particle detector is significantly lower than observed by a westward facing particle detector. During geomagnetically disturbed periods the cutoff is suppressed allowing SEPs access well inside of geosynchronous, so that the east–west SEP flux ratio approaches unity. Variations in the east–west SEP flux ratio observed by GOES Energetic Particle Sensors (EPS) have recently been reported by Rodriguez et al. (2010). In NOAA’s operational processing of EPS count rates into differential fluxes, the differential flux is treated as isotropic and flat over the energy width of the channel. To compare modeled SEP flux with GOES EPS observations, the anisotropy of the flux over the EPS energy range and field of view must be taken into account. A technique for making direct comparisons between GOES EPS observations and SEP flux modeled using numerically computed geomagnetic cutoffs is presented. Initial results from a comparison between modeled and observed flux during the 6–11 December 2006 SEP event are also presented. The modeled cutoffs reproduce the observed flux variations well but are in general too high.     

Comparison of model predictions with LDEF satellite radiation measurements.

Some early results are summarized from a program under way to utilize LDEF satellite data for evaluating and improving current models of the space radiation environment in low Earth orbit. Reported here are predictions and comparisons with some of the LDEF dose and induced radioactivity data, which are used to check the accuracy of current models describing the magnitude and directionality of the trapped proton environment. Preliminary findings are that the environment models underestimate both dose and activation from trapped protons by a factor of about two, and the observed anisotropy is higher than predicted.     

Solar-proton polar-cap intensity structures as a test of magnetic field models

The entry of energetic solar protons to the polar caps offers an interesting way to test models of the geomagnetic field. In this brief report, we present a comparison between SAMPEX observations of solar-particle intensity structure during a polar cap traversal with numerical trajectory calculations using the IGRF + T96 field model.