Geomagnetic field and altitude effects on the performance of future IACT arrays

The performance of IACT's arrays is sensitive to the altitude and geomagnetic field (GF) of the observatory site. Both effects play important role in the region of the sub-TeV gamma-ray measurements. We investigate the influence of GF on detection rates and the energy thresholds for five possible locations of the future CTA observatory using the Monte Carlo simulations. We conclude that the detection rates of gamma rays and the energy thresholds of the arrays can be fitted with linear functions of the altitude and the component of the GF perpendicular to the shower axis core. These results can be directly extrapolated for any possible localization of the CTA. In this paper we also show the influence of both geophysical effects on the images of shower and gamma/hadron separation.Comment: 4 pages, 6 figures, two-column. Contribution to ICRC 2013 proceeding

Stark effect on the exciton spectra of vertically coupled quantum dots: horizontal field orientation and non-aligned dots

We study the effect of an electric-field on an electron-hole pair in an asymmetric system of vertically coupled self-assembled quantum dots taking into account their non-perfect alignment. We show that the non-perfect alignment does not qualitatively influence the exciton Stark effect for the electric field applied in the growth direction, but can be detected by application of a perpendicular electric field. We demonstrate that the direction of the shift between the axes of non-aligned dots can be detected by rotation of a weak electric field within the plane of confinement. Already for a nearly perfect alignment the two-lowest energy bright exciton states possess antilocked extrema as function of the orientation angle of the horizontal field which appear when the field is parallel to the direction of the shift between the dot centers

Neutrinos from Early-Phase, Pulsar-Driven Supernovae

Neutron stars, just after their formation, are surrounded by expanding, dense, and very hot envelopes which radiate thermal photons. Iron nuclei can be accelerated in the wind zones of such energetic pulsars to very high energies. These nuclei photo-disintegrate and their products lose energy efficiently in collisions with thermal photons and with the matter of the envelope, mainly via pion production. When the temperature of the radiation inside the envelope of the supernova drops below $\sim 3\times 10^6$ K, these pions decay before losing energy and produce high energy neutrinos. We estimate the flux of muon neutrinos emitted during such an early phase of the pulsar - supernova envelope interaction. We find that a 1 km$^2$ neutrino detector should be able to detect neutrinos above 1 TeV within about one year after the explosion from a supernova in our Galaxy. This result holds if these pulsars are able to efficiently accelerate nuclei to energies $\sim 10^{20}$ eV, as postulated recently by some authors for models of Galactic acceleration of the extremely high energy cosmic rays (EHE CRs).Comment: 16 pages, 3 figures, revised version submitted to Ap

Gamma-rays from binary system with energetic pulsar and Be star with aspherical wind: PSR B1259-63/SS2883

At least one massive binary system containing an energetic pulsar, PSR B1259-63/SS2883, has been recently detected in the TeV gamma-rays by the HESS telescopes. These gamma-rays are likely produced by particles accelerated in the vicinity of the pulsar and/or at the pulsar wind shock, in comptonization of soft radiation from the massive star. However, the process of gamma-ray production in such systems can be quite complicated due to the anisotropy of the radiation field, complex structure of the pulsar wind termination shock and possible absorption of produced gamma-rays which might initiate leptonic cascades. In this paper we consider in detail all these effects. We calculate the gamma-ray light curves and spectra for different geometries of the binary system PSR B1259-63/SS2883 and compare them with the TeV gamma-ray observations. We conclude that the leptonic IC model, which takes into account the complex structure of the pulsar wind shock due to the aspherical wind of the massive star, can explain the details of the observed gamma-ray light curve.Comment: 12 pages, 11 figures, accepted for publication in MNRA

Electron spin and charge switching in a coupled quantum dot quantum ring system

Few-electron systems confined in a quantum dot laterally coupled to a surrounding quantum ring in the presence of an external magnetic field are studied by exact diagonalization. The distribution of electrons between the dot and the ring is influenced by the relative strength of the dot and ring confinement, the gate voltage and the magnetic field which induces transitions of electrons between the two parts of the system. These transitions are accompanied by changes in the periodicity of the Aharonov-Bohm oscillations of the ground-state angular momentum. The singlet-triplet splitting for a two electron system with one electron confined in the dot and the other in the ring exhibits piecewise linear dependence on the external field due to the Aharonov-Bohm effect for the ring-confined electron, in contrast to smooth oscillatory dependence of the exchange energy for laterally coupled dots in the side-by-side geometry.Comment: to appear in PRB in August 200