The 2.5 to 5 microns spectrum of comet Halley from the IKS instrument of Vega

Results of the 2.5–5 micron spectroscopic channel of the IKS instrument on Vega are reported and the data reduction process is described. H₂O and CO₂ molecules have been detected with production rates of 10³⁰ s⁻¹ and 1.5 10²⁸ s⁻¹ respectively. Emission features between 3.3 and 3.7 microns are tentatively attributed to CH - bearing compounds - CO is marginally detected with a mixing ratio CO/H₂O 0.2. OH emission and H₂O - ice absorption might also be present in the spectra.     

Correction to: Determining the Relative Cratering Ages of Regions of Psyche’s Surface

Space Science Reviews - Analysis of Homestake, Gallex and GNO measurements reveals evidence of variability of presumed solar-neutrino-flux measurements. Analysis of Super-Kamiokande neutrino...     

SIGMA observations of hard X-ray and soft gamma-ray emission from X-ray binaries

After more than two years of operation, the imaging γ-ray SIGMA telescope has accumulated several days of observation toward well known X-ray binaries. Four bright sources falling in this category have been detected so far: The pulsar GX 1+4 near the center of our galaxy, the stellar wind accreting system 4U 1700-377, and the black hole candidates Cygnus X-1 and GX 339-4. Moreover, SIGMA have observed three transients sources, which turned out to be also hard X-ray sources : The burster KS 1731-260, Tra X-1, and the Musca Nova. The properties of these systems in the SIGMA domain will be reviewed and a spectral distinction between black holes and neutron stars will be sketched.     

Observations of diffuse galactic positron annihilation radiation

The Galactic plane was scanned nearly three times by the UCSD/MIT Hard X-Ray and Low Energy Gamma-Ray Experiment on HEAO-1 from August 1977 through September 1978. Its Medium Energy Detectors were of the NaI/CsI phoswich type and operated over the 100 keV to 2 MeV range, with a 17° FWHM field of view and a 9% energy resolution at 511 keV. Sky maps for each epoch of observation were constructed in several energy bands. After subtraction of known point sources, a component associated with the galactic plane remains, whose spectrum is consistent with a power law and a positron annihilation spectrum. In the 333 to 583 keV energy band the flux is concentrated within ±35° of the galactic center, and the ratio of flux/radian (anticenter) is high, with a 2σ lower limit of 13. The parameters of the galactic center region's annihilation spectrum are positronium fraction of 0.9±0.1 and 511 keV flux of (2.0±0.7)×10⁻³ photons/cm²-sec-rad.     

Fractal Structure of the Heliospheric Plasma Sheet at the Earth''''s Orbit

An analysis of the data from the Wind and IMP-8 spacecraft revealed that a slow solar wind, flowing in the heliospheric plasma sheet, represents a set of magnetic tubes with plasma of increased density (N > 10cm-3 at the Earth's orbit). They have a fine structure at several spatial scales (fractality), from 2°-3°(at the Earth's orbit, it is equivalent to 3.6-5.4h, or (5.4-8.0)×106km) to the minimum about 0.025°, i.e. the angular size of the nested tubes is changed nearly by two orders of magnitude. The magnetic tubes at each observed spatial scale are diamagnetic, i.e. their surface sustains a flow of diamagnetic (or drift) current that decreases the magnetic field within the tube itself and increases it outside the tube. Furthermore, the value of β= 8π[N(Te + Tp)]/B2 within the tube exceeds the value of βoutside the tube. In many cases total pressure P = N(Te + Tp) + B2/8πis almost constant within and outside the tubes at any one of the aforementioned scales.     

Research on a complex CME event including Hα, LASCO, radio and MDI observations

We present our research on a fast and decelerating partial halo coronal mass ejection (CME) event detected in multi-wavelengths in the chromosphere and the corona on 14 October, 1999. The event involved a whole complex active area which spanned more than 40° of heliolongitude. It included a strong solar flare (XI/1N) and a complex eruptive filament within an active region of the entire complex. Especially, several radio sources were detected in the decimetric range prior to the CME by the Nançay Radioheliograph (NRH). A linear force-free field extrapolation of the Michelson Doppler Imager (MDI) magnetogram was performed to calculate the magnetic topology of the complex prior to the triggering of the event. The presence of a coronal null point combined with the occurrence of two distant and nearly simultaneous radio sources put strong arguments in favor of the generalized breakout model for the triggering of the eruption. The analysis of the subsequent development of the event suggests that large interconnecting loops were ejected together with the CME.     

2000年和2001年52°N地区OI5577气辉强度与原子氧浓度峰值的时间变化特征

分析了2000年和2001年期间52°N地区OI5577气辉强度的夜间变化特征和季节变化特征．利用由 OI5577气辉强度反演原子氧浓度峰值的方法反演出原子氧浓度的峰值,分析了峰值的夜间变化特征和季节变化特征．结果表明, OI5577气辉强度的夜间变化特征随季节变化, 2000年春季的夜间强度最大值出现在0000LT 之后,夏季和秋季的出现在0000LT之前,冬季的出现在0000LT,2001年春季和秋季的夜间强度最大值出现在0000LT之前,夏季和冬季的出现在0000LT;OI5577气辉强度在2000年2月份,8月份和10月份出现最大值,在2001年9月份有最大值．就主要特征而言,反演出的原子氧浓度峰值的夜间变化特征和季节变化特征分别与OI5577气辉强度的一致．     

Simulation Techniques for Cosmological Simulations

Modern cosmological observations allow us to study in great detail the evolution and history of the large scale structure hierarchy. The fundamental problem of accurate constraints on the cosmological parameters, within a given cosmological model, requires precise modelling of the observed structure. In this paper we briefly review the current most effective techniques of large scale structure simulations, emphasising both their advantages and shortcomings. Starting with basics of the direct N-body simulations appropriate to modelling cold dark matter evolution, we then discuss the direct-sum technique GRAPE, particle-mesh (PM) and hybrid methods, combining the PM and the tree algorithms. Simulations of baryonic matter in the Universe often use hydrodynamic codes based on both particle methods that discretise mass, and grid-based methods. We briefly describe Eulerian grid methods, and also some variants of Lagrangian smoothed particle hydrodynamics (SPH) methods.     

Particle Acceleration Mechanisms

In this paper we review the possible mechanisms for production of non-thermal electrons which are responsible for the observed non-thermal radiation in clusters of galaxies. Our primary focus is on non-thermal Bremsstrahlung and inverse Compton scattering, that produce hard X-ray emission. We first give a brief review of acceleration mechanisms and point out that in most astrophysical situations, and in particular for the intracluster medium, shocks, turbulence and plasma waves play a crucial role. We also outline how the effects of the turbulence can be accounted for. Using a generic model for turbulence and acceleration, we then consider two scenarios for production of non-thermal radiation. The first is motivated by the possibility that hard X-ray emission is due to non-thermal Bremsstrahlung by nonrelativistic particles and attempts to produce non-thermal tails by accelerating the electrons from the background plasma with an initial Maxwellian distribution. For acceleration rates smaller than the Coulomb energy loss rate, the effect of energising the plasma is to primarily heat the plasma with little sign of a distinct non-thermal tail. Such tails are discernible only for acceleration rates comparable or larger than the Coulomb loss rate. However, these tails are accompanied by significant heating and they are present for a short time of <10⁶ years, which is also the time that the tail will be thermalised. A longer period of acceleration at such rates will result in a runaway situation with most particles being accelerated to very high energies. These more exact treatments confirm the difficulty with this model, first pointed out by Petrosian (Astrophys. J. 557:560, 2001). Such non-thermal tails, even if possible, can only explain the hard X-ray but not the radio emission which needs GeV or higher energy electrons. For these and for production of hard X-rays by the inverse Compton model, we need the second scenario where there is injection and subsequent acceleration of relativistic electrons. It is shown that a steady state situation, for example arising from secondary electrons produced from cosmic ray proton scattering by background protons, will most likely lead to flatter than required electron spectra or it requires a short escape time of the electrons from the cluster. An episodic injection of relativistic electrons, presumably from galaxies or AGN, and/or episodic generation of turbulence and shocks by mergers can result in an electron spectrum consistent with observations but for only a short period of less than one billion years.