Results 1 - 10 of 1195
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[en] Extreme scattering events (ESEs) are caused by the occultation to radio sources by AU-sized objects (or lenses). Free electrons in the lens seem to be responsible for the dramatic flux changes during the occultation but the nature of the lens is still a mystery. The lens may be a peculiar lump of interstellar medium (ISM). Recent self-gravitating cloud model is very interesting in that it gives better explanation on the dual frequency light curves (DFLs) in the quasar 0954 + 658 and the cloud may be a new halo population which is sufficient to explain dark-matter problem. However, still there are many things to be clarified, such as the origin and the stability of the cloud. One of the important features of ESEs is that there are multiple events. Some of them have consecutive events caused by lenses in close angular separation. Indeed, the lenses may be clumped. For simplicity, we investigate various extreme scattering events caused by a double lens. Each lens is assumed to have an electron column density in Gaussian shape whose peak is centered. Under the assumption of point source and with typical parameter values, the double-lens model has difficulty in producing the DFL. The source size effect and stronger lensing conditions are required for the reproduction of the DFL
[en] This work examines an electrostatic charging/discharging cycle of a populated circuit board inside an equipment housing of a satellite at GEO. Component potentials and electric field strengths are examined before and after a common ground discharge event. Field reversal after the discharge suggests that favourable conditions exist for charge dissipation from dielectrics. (authors)
[en] Magnetic reconnection—the process typically lasting for a few seconds in space—is able to accelerate electrons. However, the efficiency of the acceleration during such a short period is still a puzzle. Previous analyses, based on spacecraft measurements in the Earth’s magnetotail, indicate that magnetic reconnection can enhance electron fluxes up to 100 times. This efficiency is very low, creating an impression that magnetic reconnection is not good at particle acceleration. By analyzing Cluster data, we report here a remarkable magnetic reconnection event during which electron fluxes are enhanced by 10,000 times. Such acceleration, 100 times more efficient than those in previous studies, is caused by the betatron mechanism. Both reconnection fronts and magnetic islands contribute to the acceleration, with the former being more prominent.
[en] It is showned that a double component scenario computed in a Kraichnan-like diffusion set up (which is suggested by B/C and ρ - data) gives a satisfactory fit of the recently updated measurement of the cosmic ray electron (CRE) spectrum observed by Fermi-LAT, together with PAMELA data on positron fraction. It is confirmed that nearby pulsars are good source candidates for the required e± extra-component and it is showed that the predicted CRE anisotropy in our scenario is compatible with Fermi-LAT recently published constraints.
[en] The synchrotron emission by electrons of energy greater than a few TeV in Earth's magnetic field was examined. An omnidirectional detector, it is shown, can be satisfactorily used to estimate the energy. The collecting power of the detector, it is also shown, is a sensitive function of the area of the detector, the energy of electron, and the number of photons required to identify an electron. The event rate expected was calculated using an ideal balloon-borne detector
[en] We isolated the anomalous part of the cosmic electron-positron flux within a Bayesian likelihood analysis. Using 219 recent cosmic-ray spectral data points, we inferred the values of selected cosmic-ray propagation parameters. In the context of the propagation model coded in GalProp, we found a significant tension between the electron-positron related and the rest of the fluxes. Interpreting this tension as the presence of an anomalous component in the electron-positron related data, we calculated background predictions for PAMELA and Fermi-LAT based on the non-electron-positron related fluxes. We found a deviation between the data and the predicted background even when uncertainties, including systematics, were taken into account. We identified this deviation with the anomalous electron-positron contribution. We briefly compared this model-independent signal to some theoretical results predicting such an anomaly.
[en] We present a review of the experimental results obtained by PAMELA in measuring the (p,p-bar) and e± abundance in cosmic rays. In this context, we discuss the interpretation of the observed anomalous positron excess in terms of the annihilation of dark matter particles as well as in terms of standard astrophysical sources. Moreover we show the constraints on dark matter models from p-bar data.