LM rendezvous procedures - F mission, AS-505/CSM-106/LM-4 Final report

Rendezvous procedures for LM-4 and CSM for use in crew training and flight plannin

Galactic Cosmic Rays from Supernova Remnants: II Shock Acceleration of Gas and Dust

This is the second paper (the first was astro-ph/9704267) of a series analysing the Galactic Cosmic Ray (GCR) composition and origin. In this we present a quantitative model of GCR origin and acceleration based on the acceleration of a mixture of interstellar and/or circumstellar gas and dust by supernova remnant blast waves. We present results from a nonlinear shock model which includes (i) the direct acceleration of interstellar gas-phase ions, (ii) a simplified model for the direct acceleration of weakly charged dust grains to energies of order 100keV/amu simultaneously with the gas ions, (iii) frictional energy losses of the grains colliding with the gas, (iv) sputtering of ions of refractory elements from the accelerated grains and (v) the further shock acceleration of the sputtered ions to cosmic ray energies. The calculated GCR composition and spectra are in good agreement with observations.Comment: to appear in ApJ, 51 pages, LaTeX with AAS macros, 9 postscript figures, also available from ftp://wonka.physics.ncsu.edu/pub/elliso

Index

The interest in relativistic beam-plasma instabilities has been greatly rejuvenated over the past two decades by novel concepts in laboratory and space plasmas. Recent advances in this long-standing field are here reviewed from both theoretical and numerical points of view. The primary focus is on the two-dimensional spectrum of unstable electromagnetic waves growing within relativistic, unmagnetized, and uniform electron beam-plasma systems. Although the goal is to provide a unified picture of all instability classes at play, emphasis is put on the potentially dominant waves propagating obliquely to the beam direction, which have received little attention over the years. First, the basic derivation of the general dielectric function of a kinetic relativistic plasma is recalled. Next, an overview of two-dimensional unstable spectra associated with various beam-plasma distribution functions is given. Both cold-fluid and kinetic linear theory results are reported, the latter being based on waterbag and Maxwell–Jüttner model distributions. The main properties of the competing modes (developing parallel, transverse, and oblique to the beam) are given, and their respective region of dominance in the system parameter space is explained. Later sections address particle-in-cell numerical simulations and the nonlinear evolution of multidimensional beam-plasma systems. The elementary structures generated by the various instability classes are first discussed in the case of reduced-geometry systems. Validation of linear theory is then illustrated in detail for large-scale systems, as is the multistaged character of the nonlinear phase. Finally, a collection of closely related beam-plasma problems involving additional physical effects is presented, and worthwhile directions of future research are outlined.Original Publication: Antoine Bret, Laurent Gremillet and Mark Eric Dieckmann, Multidimensional electron beam-plasma instabilities in the relativistic regime, 2010, Physics of Plasmas, (17), 12, 120501-1-120501-36. http://dx.doi.org/10.1063/1.3514586 Copyright: American Institute of Physics http://www.aip.org/</p

Fine structure in the gamma-ray sky

The EGRET results for gamma-ray intensities in and near the Galactic Plane have been analysed in some detail. Attention has been concentrated on energies above 1 GeV and the individual intensities in a $4^\circ$ longitude bin have been determined and compared with the large scale mean found from a nine-degree polynomial fit. Comparison has been made of the observed standard deviation for the ratio of these intensities with that expected from variants of our model. The basic model adopts cosmic ray origin from supernova remnants, the particles then diffusing through the Galaxy with our usual 'anomalous diffusion'. The variants involve the clustering of SN, a frequency distribution for supernova explosion energies, and 'normal', rather than 'anomalous' diffusion. It is found that for supernovae of unique energy, and our usual anomalous diffusion, clustering is necessary, particularly in the Inner Galaxy. An alternative, and preferred, situation is to adopt the model with a frequency distribution of supernova energies. The results for the Outer Galaxy are such that no clustering is required.Comment: 10 pages, 4 figures, 1 table, accepted for publication in J.Phys.G: Nucl.Part.Phy

A multifrequency study of giant radio sources-II. Spectral ageing analysis of the lobes of selected sources

Multifrequency observations with the GMRT and the VLA are used to determine the spectral breaks in consecutive strips along the lobes of a sample of selected giant radio sources (GRSs) in order to estimate their spectral ages. The maximum spectral ages estimated for the detected radio emission in the lobes of our sources range from $\sim$6 to 36 Myr with a median value of $\sim$20 Myr using the classical equipartition fields. Using the magnetic field estimates from the Beck & Krause formalism the spectral ages range from $\sim$5 to 38 Myr with a median value of $\sim$22 Myr. These ages are significantly older than smaller sources. In all but one source (J1313+6937) the spectral age gradually increases with distance from the hotspot regions, confirming that acceleration of the particles mainly occurs in the hotspots. Most of the GRSs do not exhibit zero spectral ages in the hotspots, as is the case in earlier studies of smaller sources. This is likely to be largely due to contamination by more extended emission due to relatively modest resolutions. The injection spectral indices range from $\sim$0.55 to 0.88 with a median value of $\sim$0.6. We discuss these values in the light of theoretical expectations, and show that the injection spectral index appears to be correlated with luminosity and/or redshift as well as with linear size.Comment: 12 Pages, 13 Figures, 9 Tables, Accepted for publication in MNRA

Nonthermal Bremsstrahlung and Hard X-ray Emission from Clusters of Galaxies

We have calculated nonthermal bremsstrahlung (NTB) models for the hard X-ray (HXR) tails recently observed by BeppoSAX in clusters of galaxies. In these models, the HXR emission is due to suprathermal electrons with energies of about 10-200 keV. Under the assumption that the suprathermal electrons form part of a continuous spectrum of electrons including highly relativistic particles, we have calculated the inverse Compton (IC) extreme ultraviolet (EUV), HXR, and radio synchrotron emission by the extensions of the same populations. For accelerating electron models with power-law momentum spectra (N[p] propto p^{- mu}) with mu <~ 2.7, which are those expected from strong shock acceleration, the IC HXR emission exceeds that due to NTB. Thus, these models are only of interest if the electron population is cut-off at some upper energy <~1 GeV. Similarly, flat spectrum accelerating electron models produce more radio synchrotron emission than is observed from clusters if the ICM magnetic field is B >~ 1 muG. The cooling electron model produces vastly too much EUV emission as compared to the observations of clusters. We have compared these NTB models to the observed HXR tails in Coma and Abell 2199. The NTB models require a nonthermal electron population which contains about 3% of the number of electrons in the thermal ICM. If the suprathermal electron population is cut-off at some energy above 100 keV, then the models can easily fit the observed HXR fluxes and spectral indices in both clusters. For accelerating electron models without a cutoff, the electron spectrum must be rather steep >~ 2.9.Comment: Accepted for publication in the Astrophysical Journal. 10 pages with 5 embedded Postscript figures in emulateapj.sty. An abbreviated abstract follow

Nonthermal Emission from a Supernova Remnant in a Molecular Cloud

In evolved supernova remnants (SNRs) interacting with molecular clouds, such as IC 443, W44, and 3C391, a highly inhomogeneous structure consisting of a forward shock of moderate Mach number, a cooling layer, a dense radiative shell and an interior region filled with hot tenuous plasma is expected. We present a kinetic model of nonthermal electron injection, acceleration and propagation in that environment and find that these SNRs are efficient electron accelerators and sources of hard X- and gamma-ray emission. The energy spectrum of the nonthermal electrons is shaped by the joint action of first and second order Fermi acceleration in a turbulent plasma with substantial Coulomb losses. Bremsstrahlung, synchrotron, and inverse Compton radiation of the nonthermal electrons produce multiwavelength photon spectra in quantitative agreement with the radio and the hard emission observed by ASCA and EGRET from IC 443. We distinguish interclump shock wave emission from molecular clump shock wave emission accounting for a complex structure of molecular cloud. Spatially resolved X- and gamma- ray spectra from the supernova remnants IC 443, W44, and 3C391 as might be observed with BeppoSAX, Chandra XRO, XMM, INTEGRAL and GLAST would distinguish the contribution of the energetic lepton component to the gamma-rays observed by EGRET.Comment: 14 pages, 4 figure, Astrophysical Journal, v.538, 2000 (in press

Analytic solution for nonlinear shock acceleration in the Bohm limit

The selfconsistent steady state solution for a strong shock, significantly modified by accelerated particles is obtained on the level of a kinetic description, assuming Bohm-type diffusion. The original problem that is commonly formulated in terms of the diffusion-convection equation for the distribution function of energetic particles, coupled with the thermal plasma through the momentum flux continuity equation, is reduced to a nonlinear integral equation in one variable. Its solution provides selfconsistently both the particle spectrum and the structure of the hydrodynamic flow. A critical system parameter governing the acceleration process is found to be $\Lambda = M^{-3/4}\Lambda_1$, where $\Lambda_1 =\eta p_1/mc$, with a suitably normalized injection rate $\eta$, the Mach number M >> 1, and the cut-off momentum $p_1$. We particularly focus on an efficient solution, in which almost all the energy of the flow is converted into a few energetic particles. It was found that (i) for this efficient solution (or, equivalently, for multiple solutions) to exist, the parameter $\zeta =\eta\sqrt{p_0 p_1}/mc$ must exceed a critical value $\zeta_{cr} \sim 1$ ($p_0$ is the injection momentum), (ii) the total shock compression ratio r increases with M and saturates at a level that scales as $ r \propto \Lambda_1 (iii) the downstream power-law spectrum has the universal index q=3.5 over a broad momentum range. (iv) completely smooth shock transitions do not appear in the steady state kinetic description.Comment: 39 pages, 3 PostScript figures, uses aasms4.sty, to appear in Aug. 20, 1997 issue ApJ, vol. 48

A New Measurement of Cosmic Ray Composition at the Knee

The Dual Imaging Cerenkov Experiment (DICE) was designed and operated for making elemental composition measurements of cosmic rays near the knee of the spectrum at several PeV. Here we present the first results using this experiment from the measurement of the average location of the depth of shower maximum, , in the atmosphere as a function of particle energy. The value of near the instrument threshold of ~0.1 PeV is consistent with expectations from previous direct measurements. At higher energies there is little change in composition up to ~5 PeV. Above this energy is deeper than expected for a constant elemental composition implying the overall elemental composition is becoming lighter above the knee region. These results disagree with the idea that cosmic rays should become on average heavier above the knee. Instead they suggest a transition to a qualitatively different population of particles above 5 PeV.Comment: 7 pages, LaTeX, two eps figures, aas2pp4.sty and epsf.sty included, accepted by Ap.J. Let

Exact Expressions for the Critical Mach Numbers in the Two-Fluid Model of Cosmic-Ray Modified Shocks

The acceleration of relativistic particles due to repeated scattering across a shock wave remains the most attractive model for the production of energetic cosmic rays. This process has been analyzed extensively during the past two decades using the ``two-fluid'' model of diffusive shock acceleration. It is well known that 1, 2, or 3 distinct solutions for the flow structure can be found depending on the upstream parameters. The precise nature of the critical conditions delineating the number and character of shock transitions has remained unclear, mainly due to the inappropriate choice of parameters used in the determination of the upstream boundary conditions. We derive the exact critical conditions by reformulating the upstream boundary conditions in terms of two individual Mach numbers defined with respect to the cosmic-ray and gas sound speeds, respectively. The gas and cosmic-ray adiabatic indices are assumed to remain constant throughout the flow, although they may have arbitrary, independent values. Our results provide for the first time a complete, analytical classification of the parameter space of shock transitions in the two-fluid model. When multiple solutions are possible, we propose using the associated entropy distributions as a means for indentifying the most stable configuration.Comment: Accepted for publication in ApJ; corrected a few typos; added journal re