Nucleonic gamma-ray production in Pulsar Wind Nebulae

Observations of the inner radian of the Galactic disk at very high energy (VHE) gamma-rays have revealed at least 16 new sources. Besides shell type super-nova remnants, pulsar wind nebulae (PWN) appear to be a dominant source population in the catalogue of VHE gamma-ray sources. Except for the Crab nebula, the newly discovered PWN are resolved at VHE gamma-rays to be spatially extended (5-20 pc). Currently, at least 3 middle aged ($t>10$ kyrs) PWN (Vela X, G18.0-0.7, and G313.3+0.6 in the ``Kookaburra'' region) and 1 young PWN MSH 15-5{\it2} ($t=1.55$ kyrs) have been identified to be VHE emitting PWN (sometimes called ``TeV Plerions''). Two more candidate ``TeV Plerions'' have been identifed and have been reported at this conference [1]. In this contribution, the gamma-ray emission from Vela X is explained by a nucleonic component in the pulsar wind. The measured broad band spectral energy distribution is compared with the expected X-ray emission from primary and secondary electrons. The observed X-ray emission and TeV emission from the three middle aged PWN are compared with each other.Comment: 6 pages, 3 figures, to appear in proceedings "The Multi-Messenger Approach to High-Energy Gamma-Ray Sources", Barcelona July 200

Implications of H.E.S.S. observations of pulsar wind nebulae

In this review paper on pulsar wind nebulae (PWN) we discuss the properties of such nebulae within the context of containment against cross-field diffusion (versus normal advection), the effect of reverse shocks on the evolution of offset ``Vela-like'' PWN, constraints on maximum particle energetics, magnetic field strength estimates based on spectral and spatial properties, and the implication of such field estimates on the composition of the wind. A significant part of the discussion is based on the High Energy Stereoscopic System ({\it H.E.S.S.} or {\it HESS}) detection of the two evolved pulsar wind nebulae Vela X (cocoon) and HESS J1825-137. In the case of Vela X (cocoon) we also review evidence of a hadronic versus a leptonic interpretation, showing that a leptonic interpretation is favored for the {\it HESS} signal. The constraints discussed in this review paper sets a general framework for the interpretation of a number of offset, filled-center nebulae seen by {\it HESS}. These sources are found along the galactic plane with galactic latitudes $|b|\sim 0$, where significant amounts of molecular gas is found. In these regions, we find that the interstellar medium is inhomogeneous, which has an effect on the morphology of supernova shock expansion. One consequence of this effect is the formation of offset pulsar wind nebulae as observed.Comment: to appear in Springer Lecture Notes on Neutron Stars and Pulsars: 40 years after their discovery, eds. W. Becke

Modelling Jets, Tori and Flares in Pulsar Wind Nebulae

In this contribution we review the recent progress in the modelling of Pulsar Wind Nebulae (PWN). We start with a brief overview of the relevant physical processes in the magnetosphere, the wind-zone and the inflated nebula bubble. Radiative signatures and particle transport processes obtained from 3D simulations of PWN are discussed in the context of optical and X-ray observations. We then proceed to consider particle acceleration in PWN and elaborate on what can be learned about the particle acceleration from the dynamical structures called GwispsG observed in the Crab nebula. We also discuss recent observational and theoretical results of gamma-ray flares and the inner knot of the Crab nebula, which had been proposed as the emission site of the flares. We extend the discussion to GeV flares from binary systems in which the pulsar wind interacts with the stellar wind from a companion star. The chapter concludes with a discussion of solved and unsolved problems posed by PWN

Crystal-field splitting in Pr dideuteride

From inelastic neutron scattering experiments, it is concluded that the crystal-field splitting in PrD/sub 1.95/ is 41 meV. Because of this high value, the antiferromagnetic ordering below T/sub N/ = 2.3 K is ascribed to a magnetic ground state, probably GAMMA/sub 5/, of the Pr/sup 3 +/ ions

Granularity effects on the magnetic and electrical properties of La(Ca,Sr)MnO3 thin films

The influence of the grains and the grain boundaries on the resistivity in polycrystalline La0,7(Sr,Ca)0,3MnO3 has been investigated by impedance spectroscopy measurements of thin films, that are prepared by a chemical solution deposition. The results reveal grain boundary regions with a high resistivity, in contrast to the low resistivity behaviour of the bulk, equal to that of epitaxial thin films