Implications of X-ray Observations for Electron Acceleration and Propagation in Solar Flares

High-energy X-rays and ??-rays from solar flares were discovered just over fifty years ago. Since that time, the standard for the interpretation of spatially integrated flare X-ray spectra at energies above several tens of keV has been the collisional thick-target model. After the launch of the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) in early 2002, X-ray spectra and images have been of sufficient quality to allow a greater focus on the energetic electrons responsible for the X-ray emission, including their origin and their interactions with the flare plasma and magnetic field. The result has been new insights into the flaring process, as well as more quantitative models for both electron acceleration and propagation, and for the flare environment with which the electrons interact. In this article we review our current understanding of electron acceleration, energy loss, and propagation in flares. Implications of these new results for the collisional thick-target model, for general flare models, and for future flare studies are discussed.     

Properties of Near-Earth Magnetic Reconnection from In-Situ Observations

Many properties of magnetic reconnection have been determined from in-situ spacecraft observations in the Earth??s magnetosphere. Recent studies have focused on ion scale lengths and have largely confirmed theoretical predictions. In addition, some interesting features of reconnection regions on electron scale lengths have been identified. These recent studies have demonstrated the need for combined plasma and field measurements on electron scale lengths in the reconnection diffusion regions at the magnetopause and in the magnetotail. They have also indicated that measurements, such as those that will be made by the Magnetospheric Multiscale mission in the near future, will have a significant impact on understanding magnetic reconnection as a fundamental plasma process.     

Hard X-ray structure of the Crab Nebula

Two-dimensional maps of the Crab Nebula have been synthesized in 22–64 keV range through the modulation collimator experiment. The effective angular resolution is about 15. The result indicates that the Crab morphology is strictly controlled by the pulsar.     

Hard X-ray balloon observations of compact galactic and extragalactic X-ray sources

A balloon program in hard X-ray astronomy (20–200 keV) is jointly pursued by the Astronomisches Institut der Universität Tübingen (AIT) and the Max Planck-Institute für Extraterrestrische Physik in Garching (MPE). Since 1973 nine successful balloon flights have been performed from Texas and Australia. Here results on Centaurus A and on several galactic binary X-ray sources are summarized. In particular the high energy photon spectrum of Hercules X-1 and the evidence for the cyclotron line feature which was discovered by us in 1976 is reviewed.     

Deducing turbulence parameters from transionospheric scintillation measurements

The theoretical framework and experimental methodology used to interpret observations of ionospheric scintillations in terms of geophysical processes are reviewed and recent experimental observations of ionospheric scintillations are discussed in this paper. During the past 15 years significant progress has been made in several areas. In particular, significant advances have been made in theoretical understanding of the strong scintillation regime and the effects of short-term temporal variations of the scintillation producing irregularities on observations made with spaced-receiver geometries in both weak and strong scintillations. This improved understanding of the scintillation process has significantly increased the utility of the technique particularly in the equatorial latitudes where geometrical effects are least important.     

Hard X-ray observations of the eclipsing binary EX Hydrae

We present light curves of EX Hydrae in the 1–10 keV range obtained with the medium energy experiment of EXOSAT. The 67-min modulation was observed with a peak-to-peak amplitude of 36 % in the 1–4 keV range and of 24 % in the 4–9 keV range. Newly discovered was a partial X-ray eclipse of 3 min full width which coincides with the optical eclipse and is seen at all energies. The results are interpreted in terms of an intermediate-polar (DQ Her star) model of EX Hydrae.     

Loop Models from SOHO Observations

The Coronal Diagnostic Spectrometer (CDS) on SOHO is a grazing/normal incidence spectrograph, aimed to produce stigmatic spectra of selected regions of the solar surface in six spectral windows of the extreme ultraviolet from 150 Å to 785 Å (Harrison et al. 1995). In the present work, CDS, EIT, MDI and Yohkoh observations of active region lops have been analyzed. These observations are part of JOP 54. CDS monochromatic images from lines at different temperatures have been co-aligned with EIT and MDI images, and loop structures have been clearly identified using Fe XVI emission lines. Density sensitive lines and lines from adjacent stages of ionization of Fe ions have been used to measure electron density and temperature along the loop length; these measurements have been used to determine the electron pressure along the loop and test the constant pressure assumption commonly used in loop modeling. The observations have been compared with a static, isobaric loop model (Landini and Monsignori Fossi 1975) assuming a temperature-constant heating function in the energy balance equation. Good agreement is found for the temperature distribution along the loop at the coronal level. The model pressure is somewhat higher than obtained from density sensitive line ratios.     

X-ray emission from Be star/X-ray binaries

Observations of X-ray emission from Be star/X-ray binaries are reviewed. Some optical characteristics of these binaries are also presented. Theoretical aspects pertaining to the X-ray emissions are given.     

压力对有序LixTiS2电子性质的影响

采用基于密度泛函理论的局域密度近似（LDA）,计算了压力对LixTiS2（x=0.0．25,0．5,0．75,1）的晶格结构和电子结构的影响。研究发现,对于同一“含量的LixTiS2,随着压力的增大,LixTiS2的晶格参数有规律的减小,插层化合物中Li的含量越高,材料越难被压缩;在压强等于1GPa左右时各体系的总能量达到最小值。各体系的费米能级随着压力的增大而降低;各原子的电子能态密度产生了漂移,压力还导致了S原子和．Ti原子p-d杂化减弱。“原子和S原子的共价相互作用得到了增强     

Solar Wind Electron Observations Near Solar Maximum at High Latitudes From Thermal Noise Spectroscopy

The Ulysses spacecraft is reaching high heliolatitudes during the approach to solar maximum. We show preliminary in situ electron observations from the URAP experiment, using thermal noise spectroscopy. This method is especially suited to measure accurately the electron density and thermal temperature. The data acquired in the period June–September 2000 are compared to those obtained at similar heliolatitudes near solar activity minimum and in the ecliptic plane near both solar maximum and minimum. This revised version was published online in August 2006 with corrections to the Cover Date.     

Orbit Determination from Passive Range Observations

An experiment is described by which the ephemeris of a near-synchronous satellite was determined from passive range observations. The data consist of the measured times of reception at ground tracking stations of electromagnetic signals which are radiated from the satellite at regular intervals. A comparison of the ephemeris to one obtained from Doppler tracking indicates an accuracy of better than 4.9 mrad rms.     

电子束固化高模量纤维增强复合材料力学性能研究

用湿法缠绕工艺制备了M40／EB99—1预浸料，研究了电子束固化高模量石墨化碳纤维M40增强EB99-1环氧树脂复合材料的常规力学性能、耐热疲劳性能和热物理性能，并与M40／5228、M40/4211等热固化复合材料的性能进行了比较。实验研究表明，除了剪切强度稍逊于热固化M40/5228复合材料外，其它常规力学性能都优于热固化M40／5228、M40/211复合材料，表现了较好的综合力学性能。电子束固化M40／EB99—1复合材料经冷热交变循环后的性能明显优于热固化M40／5228、M40/4211复合材料，表现了较好的耐热疲劳性能。     

X-ray emission from cataclysmic variables

EXOSAT results on cataclysmic variables are reviewed. The long continuous X-ray observations afforded by this observatory, coupled with the sensitivity of its instruments to medium energy and very low energy X-rays, have enabled the rotational and orbital X-ray light curves of these stars to be measured in unprecedented detail. Examples are given of data on synchronously and asynchronously rotating magnetic systems, and on disc accreting stars. The impact of the new observations on our understanding of cataclysmic variables is discussed.     

High X-ray luminosity from dynamo stars

In the present work we intend to show that a stellar dynamo mechanism can produce high X-ray luminosities and also give account for modulation periods of the order thousand seconds or larger.We outline here that the model we propose does not require the presence of a very compact object in a binary system; indeed, we intend to show that faint late main sequence stars sufficiently fast rotating, can give rise by dynamo action to sufficiently high magnetic fields to give account for the strong X-ray emission of some galactic X-ray sources.We examine the possibility that also a fraction of those X-ray sources usually depicted as accreting binary systems may be interpreted as active stars supplied by the - dynamo mechanism.     

X-ray emission from clusters of galaxies

The X-ray emission from the intracluster gas is a rich source of information on the metal abundance, evolution and mass profile of clusters. Methods for determining the mass of gas are reviewed; the total mass is uncertain. The best data so far available concentrate on the cluster core. Cooling flows are found within the cores of a significant fraction of rich and poor clusters, as well as in relatively isolated elliptical galaxies.