10,498 research outputs found
Multi-wavelength observations of the gamma-ray flaring quasar S4 1030+61 in 2009-2014
We present a study of the parsec-scale multi-frequency properties of the
quasar S4 1030+61 during a prolonged radio and gamma-ray activity. Observations
were performed within Fermi gamma-ray telescope, OVRO 40-m telescope and MOJAVE
VLBA monitoring programs, covering five years from 2009. The data are
supplemented by four-epoch VLBA observations at 5, 8, 15, 24, and 43 GHz, which
were triggered by the bright gamma-ray flare, registered in the quasar in 2010.
The S4 1030+61 jet exhibits an apparent superluminal velocity of (6.4+-0.4)c
and does not show ejections of new components in the observed period, while
decomposition of the radio light curve reveals nine prominent flares. The
measured variability parameters of the source show values typical for
Fermi-detected quasars. Combined analysis of radio and gamma-ray emission
implies a spatial separation between emitting regions at these bands of about
12 pc and locates the gamma-ray emission within a parsec from the central
engine. We detected changes in the value and direction of the linear
polarization and the Faraday rotation measure. The value of the intrinsic
brightness temperature of the core is above the equipartition state, while its
value as a function of distance from the core is well approximated by the
power-law. Altogether these results show that the radio flaring activity of the
quasar is accompanied by injection of relativistic particles and energy losses
at the jet base, while S4 1030+61 has a stable, straight jet well described by
standard conical jet theories.Comment: accepted by MNRAS, 16 pages, 14 figures, 8 tables, 5 pages of
supplementary materia
Comment on "Interaction Effects in Conductivity of Si Inversion Layers at Intermediate Temperatures"
We show that the comparison between theory and experiment, performed by
Pudalov et al. in PRL 91, 126403 (2003), is not valid.Comment: comment on PRL 91, 126403 (2003) by Pudalov et a
Spin Degree of Freedom in a Two-Dimensional Electron Liquid
We have investigated correlation between spin polarization and
magnetotransport in a high mobility silicon inversion layer which shows the
metal-insulator transition. Increase in the resistivity in a parallel magnetic
field reaches saturation at the critical field for the full polarization
evaluated from an analysis of low-field Shubnikov-de Haas oscillations. By
rotating the sample at various total strength of the magnetic field, we found
that the normal component of the magnetic field at minima in the diagonal
resistivity increases linearly with the concentration of ``spin-up'' electrons.Comment: 4 pages, RevTeX, 6 eps-figures, to appear in PR
Magnetoresistance of a two-dimensional electron gas in a parallel magnetic field
The conductivity of a two-dimensional electron gas in a parallel magnetic
field is calculated. We take into account the magnetic field induced
spin-splitting, which changes the density of states, the Fermi momentum and the
screening behavior of the electron gas. For impurity scattering we predict a
positive magnetoresistance for low electron density and a negative
magnetoresistance for high electron density. The theory is in qualitative
agreement with recent experimental results found for Si inversion layers and Si
quantum wells.Comment: 4 pages, figures included, PDF onl
Magnetic Field Suppression of the Conducting Phase in Two Dimensions
The anomalous conducting phase that has been shown to exist in zero field in
dilute two-dimensional electron systems in silicon MOSFETs is driven into a
strongly insulating state by a magnetic field of about 20 kOe applied parallel
to the plane. The data suggest that in the limit of T -> 0 the conducting phase
is suppressed by an arbitrarily weak magnetic field. We call attention to
striking similarities to magnetic field-induced superconductor-insulator
transitions
A New Liquid Phase and Metal-Insulator Transition in Si MOSFETs
We argue that there is a new liquid phase in the two-dimensional electron
system in Si MOSFETs at low enough electron densities. The recently observed
metal-insulator transition results as a crossover from the percolation
transition of the liquid phase through the disorder landscape in the system
below the liquid-gas critical temperature. The consequences of our theory are
discussed for variety of physical properties relevant to the recent
experiments.Comment: 12 pages of RevTeX with 3 postscript figure
Superconductivity in correlated disordered two-dimensional electron gas
We calculate the dynamic effective electron-electron interaction potential
for a low density disordered two-dimensional electron gas. The disordered
response function is used to calculate the effective potential where the
scattering rate is taken from typical mobilities from recent experiments. We
investigate the development of an effective attractive pair potential for both
disordered and disorder free systems with correlations determined from existing
numerical simulation data. The effect of disorder and correlations on the
superconducting critical temperature Tc is discussed.Comment: 4 pages, RevTeX + epsf, 4 figure
Hall Coefficient of a Dilute 2D Electron System in Parallel Magnetic Field
Measurements in magnetic fields applied at a small angle with respect to the
2D plane of the electrons of a low-density silicon MOSFET indicate that the
Hall coefficient is independent of parallel field from H=0 to , the
field above which the longitudinal resistance saturates and the electrons have
reached full spin-polarization. This implies that the mobilities of the spin-up
and spin-down electrons remain comparable at all magnetic fields, and suggests
there is strong mixing of spin-up and spin-down electron states.Comment: 4 pages, 2 figure
- …