Relativistic Proton Production During the 14 July 2000 Solar Event: The Case for Multiple Source Mechanisms

Protons accelerated to relativistic energies by transient solar and interplanetary phenomena caused a ground-level cosmic ray enhancement on 14 July 2000, Bastille Day. Near-Earth spacecraft measured the proton flux directly and ground-based observatories measured the secondary responses to higher energy protons. We have modelled the arrival of these relativistic protons at Earth using a technique which deduces the spectrum, arrival direction and anisotropy of the high-energy protons that produce increased responses in neutron monitors. To investigate the acceleration processes involved we have employed theoretical shock and stochastic acceleration spectral forms in our fits to spacecraft and neutron monitor data. During the rising phase of the event (10:45 UT and 10:50 UT) we find that the spectrum between 140 MeV and 4 GeV is best fitted by a shock acceleration spectrum. In contrast, the spectrum at the peak (10:55 UT and 11:00 UT) and in the declining phase (11:40 UT) is best fitted with a stochastic acceleration spectrum. We propose that at least two acceleration processes were responsible for the production of relativistic protons during the Bastille Day solar event: (1) protons were accelerated to relativistic energies by a shock, presumably a coronal mass ejection (CME). (2) protons were also accelerated to relativistic energies by stochastic processes initiated by magnetohydrodynamic (MHD) turbulence.Comment: 38 pages, 9 figures, accepted for publication in the Astrophysical Journal, January, 200

Spin-polarization-induced structural selectivity in Pd3X_3X and Pt3X_3X (X=3dX=3d) compounds

Spin-polarization is known to lead to important {\it magnetic} and {\it optical} effects in open-shell atoms and elemental solids, but has rarely been implicated in controlling {\it structural} selectivity in compounds and alloys. Here we show that spin-polarized electronic structure calculations are crucial for predicting the correct $T=0$ crystal structures for Pd$_3X$ and Pt$_3X$ compounds. Spin-polarization leads to (i) stabilization of the $L1_2$ structure over the $DO_{22}$ structure in Pt$_3$Cr, Pd$_3$Cr, and Pd$_3$Mn, (ii) to the stabilization of the $DO_{22}$ structure over the $L1_2$ structure in Pd$_3$Co and to (iii) ordering (rather than phase-separation) in Pt$_3$Co and Pd$_3$Cr. The results are analyzed in terms of first-principles local spin density calculations.Comment: 4 pages, REVTEX, 3 eps figures, to appear in PR

Deflection of ultra high energy cosmic rays by the galactic magnetic field: from the sources to the detector

We report the results of 3D simulations of the trajectories of ultra-high energy protons and Fe nuclei (with energies $E = 4 \times 10^{19}$ and $2.5 \times 10^{20} eV$) propagating through the galactic magnetic field from the sources to the detector. A uniform distribution of anti-particles is backtracked from the detector, at the Earth, to the halo of the Galaxy. We assume an axisymmetric, large scale spiral magnetic field permeating both the disc and the halo. A normal field component to the galactic plane ($B_z$) is also included in part of the simulations. We find that the presence of a large scale galactic magnetic field does not generally affect the arrival directions of the protons, although the inclusion of a $B_z$ component may cause significant deflection of the lower energy protons ($E = 4 \times 10^{19}$ eV). Error boxes larger than or equal to $\sim 5^{\circ}$ are most expected in this case. On the other hand, in the case of heavy nuclei, the arrival direction of the particles is strongly dependent on the coordinates of the particle source. The deflection may be high enough ($> 20^{\circ}$) as to make extremely difficult any identification of the sources unless the real magnetic field configuration is accurately determined. Moreover, not every incoming particle direction is allowed between a given source and the detector. This generates sky patches which are virtually unobservable from the Earth. In the particular case of the UHE events of Yakutsk, Fly's Eye, and Akeno, they come from locations for which the deflection caused by the assumed magnetic field is not significant.Comment: LaTeX + 2 postscript figures - Color versions of both figures (highly recommended) available via anonymous ftp at ftp://capc07.ast.cam.ac.uk/pub/uhecr_gmf as fig*.g

Energetic Electron Bursts in the Magnetopause Electron Layer and in Interplanetary Space

The magnetopause electron layer in the distant magnetotail is an annular region encircling the magnetopause in which bursts of tailward-streaming energetic (E > 200 keV) electrons are almost continually present. Sunward-streaming electron bursts with time scales and energy spectral indices similar to those of layer bursts are sometimes observed in interplanetary space upstream of the earth. Evidence is presented to show that the layer bursts and the interplanetary bursts have a common source. With the aid of a new coordinate system -- geocentric interplanetary medium (GIPM) coordinates -- appropriate for describing the access of energetic charged p[articles in the inner magnetosheath to a spacecraft located in interplanetary space, it is shown that the interplanetary bursts occur predominately on the sunward extension of the field lines associated with the magnetopause electron layer

Integration of formal fault analysis in ASSERT: Case studies and lessons learnt

International audienceThe ASSERT European Integrated Project (Automated proof-based System and Software Engineering for Real-Time systems; EC FP6, IST-004033) has investigated, elaborated and experimented advanced methods based on the AltaRica language and support tool OCAS for architecture and fault approach propagation description analysis, and integrated in the complete ASSERT process. The paper describes lessons learnt from three case studies: safety critical spacecraft, autonomous deep exploration spacecraft, and civil aircraft