The time evolution of GRB spectra by a precessing lighthouse Gamma Jet

Inverse Compton Scattering (ICS) by a relativistic electron beam jet at GeV energies (emitted by a compact object as a NS, BH,...), a NSJ, onto thermal BBR photons (from a nearby stellar companion) may originate a collinear gamma jet (GJ). Due to the binary system interaction the GJ precession would blaze suddenly toward the observer leading to a GRB event. The internal GJ cone structure is ruled by relativistic kinematics into a concentric onion-like sequence of photon rings, the softer in the external boundaries, the harder in the inner cone. The pointing and the crossing of such different GJ photon rings to the detector lead to a GRB hardness spectra evolution nearly corresponding to most observed ones. Moreover expected time integral spectra are also comparable with known GRB spectra. The total energy input of tens of thousands of such NSJ in an extended galactic halo, mainly cosmic rays electrons, should be reflected into the recent observational evidence (COMPTEL) of a diffused relic extended halo. Evidences of such precessing jets are offered by the discover of galactic superluminal sources, recent HH jets, SN1987A outer rings, Hourglass Nebula, planetary Egg Nebula, GROJ1744-28 binary X-rays pulsar

Signatures of dynamically polarized nuclear spins in all-electrical lateral spin transport devices

The effect of nuclear spins in Fe/GaAs all-electrical spin-injection devices is investigated. At temperatures below 50 K, strong modifications of the non-local spin signal are found that are characteristic for hyperfine coupling between conduction electrons and dynamically polarized nuclear spins. The perpendicular component of the nuclear Overhauser field depolarizes electron spins near zero in-plane external magnetic field, and can suppress such dephasing when antialigned with the external field, leading to satellite peaks in a Hanle measurement. The features observed agree well with a Monte Carlo simulation of the spin diffusion equation including hyperfine interaction, and are used to study the nuclear spin dynamics and relate it to the spin polarization of injected electrons.Comment: 6 pages, 4 figure

Inverse Compton Scattering onto BBR in High Energy Physics and Gamma (MeV-Tev) Astrophysics

We considered the Inverse Compton Scattering (ICS) of charged particles onto photons whose distribution is a Black Body Radiation (BBR) deriving the exact energy and angular differential distribution in the general case and in its most useful expansions. These results can be successfully applied in high energy accelerators experiments to evaluate the ICS contribution from the thermal photons in the cavity as well as in astrophysics where the ICS of cosmic rays plays a relevant role in a variety of phenomena. In particular we show how our formulae reproduce the ICS energy spectrum recently measured at LEP, how it could be considered a key tool in explaining the Gamma Ray Bursts (GRB) , SGRs energy spectrum. Finally we predicted the presence of a low gamma flux, nearly detectable at hundred of TeV from SNRs SN1006 as well as, at lower energy (tens TeV, due to gamma ray cascading in cosmic BBR), from relic extragalactic highest cosmic rays sources born by jets in AGN,as blazars 3C279,Mrk421,Mrk 501.Comment: Latex file , 10 figures can be found via anonymous ftp in ftp://hpteo.roma1.infn.it/pub/preprints/fargion/newicsartfig.tex and fig1.ps - fig10.p

Temperature dependence of the nonlocal voltage in an Fe/GaAs electrical spin injection device

The nonlocal spin resistance is measured as a function of temperature in a Fe/GaAs spin-injection device. For nonannealed samples that show minority-spin injection, the spin resistance is observed up to room temperature and decays exponentially with temperature at a rate of 0.018\,K$^{-1}$. Post-growth annealing at 440\,K increases the spin signal at low temperatures, but the decay rate also increases to 0.030\,K$^{-1}$. From measurements of the diffusion constant and the spin lifetime in the GaAs channel, we conclude that sample annealing modifies the temperature dependence of the spin transfer efficiency at injection and detection contacts. Surprisingly, the spin transfer efficiency increases in samples that exhibit minority-spin injection.Comment: 10 pages, 4 figure

Mode Spectroscopy and Level Coupling in Ballistic Electron Waveguides

A tunable quantum point contact with modes occupied in both transverse directions is studied by magnetotransport experiments. We use conductance quantization of the one-dimensional subbands as a tool to determine the mode spectrum. A magnetic field applied along the direction of the current flow couples the modes. This can be described by an extension of the Darwin-Fock model. Anticrossings are observed as a function of the magnetic field, but not for zero field or perpendicular field directions, indicating coupling of the subbands due to nonparabolicity in the electrical confinement.Comment: 4 pages, 3 figure