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991.
Marchi S. Asphaug E. Bell J. F. Bottke W. F. Jaumann R. Park R. S. Polanskey C. A. Prettyman T. H. Williams D. A. Binzel R. Oran R. Weiss B. Russell C. T. 《Space Science Reviews》2022,218(4):1-28
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... 相似文献
992.
P. Laurent A. Claret F. Lebrun J. Paul M. Dennis D. Barret L. Bouchet P. Mandrou R. Sunyaev E. Churazov M. Gilfanov N. Khavenson A. Dyachkov B. Novikov R. Kremnev V. Kovtunenko 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1993,13(12):139-148
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. 相似文献
993.
M. S. Briggs D. E. Gruber J. L. Matteson L. E. Peterson 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1993,13(12):709-713
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. 相似文献
994.
995.
S.J. Wang D. Maia M. Pick G. Aulanier J.-M. Malherbe J.-P. Delaboudinire 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2005,36(12):2273
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. 相似文献
996.
Non-thermal components are key ingredients for understanding clusters of galaxies. In the hierarchical model of structure
formation, shocks and large-scale turbulence are unavoidable in the cluster formation processes. Understanding the amplification
and evolution of the magnetic field in galaxy clusters is necessary for modelling both the heat transport and the dissipative
processes in the hot intra-cluster plasma. The acceleration, transport and interactions of non-thermal energetic particles
are essential for modelling the observed emissions. Therefore, the inclusion of the non-thermal components will be mandatory
for simulating accurately the global dynamical processes in clusters. In this review, we summarise the results obtained with
the simulations of the formation of galaxy clusters which address the issues of shocks, magnetic field, cosmic ray particles
and turbulence. 相似文献
997.
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. 相似文献
998.
K. Dolag S. Borgani S. Schindler A. Diaferio A. M. Bykov 《Space Science Reviews》2008,134(1-4):229-268
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. 相似文献
999.
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. 相似文献
1000.
F. Durret J. S. Kaastra J. Nevalainen T. Ohashi N. Werner 《Space Science Reviews》2008,134(1-4):51-70
An excess over the extrapolation to the extreme ultraviolet and soft X-ray ranges of the thermal emission from the hot intracluster
medium has been detected in a number of clusters of galaxies. We briefly present each of the satellites (EUVE, ROSAT PSPC
and BeppoSAX, and presently XMM-Newton, Chandra and Suzaku) and their corresponding instrumental issues, which are responsible
for the fact that this soft excess remains controversial in a number of cases. We then review the evidence for this soft X-ray
excess and discuss the possible mechanisms (thermal and non-thermal) which could be responsible for this emission. 相似文献