5,164 research outputs found
Temporal and Spectral Variabilities of High Energy Emission from Blazars Using Synchrotron Self-Compton Models
Multiwavelength observations of blazars such as Mrk 421 and Mrk 501 show that
they exhibit strong short time variabilities in flare-like phenomena. Based on
the homogeneous synchrotron self-Compton (SSC) model and assuming that time
variability of the emission is initiated by changes in the injection of
nonthermal electrons, we perform detailed temporal and spectral studies of a
purely cooling plasma system. One important parameter is the total injected
energy E and we show how the synchrotron and Compton components respond as E
varies. We discuss in detail how one could infer important physical parameters
using the observed spectra. In particular, we could infer the size of the
emission region by looking for exponential decay in the light curves. We could
also test the basic assumption of SSC by measuring the difference in the rate
of peak energy changes of synchrotron and SSC peaks. We also show that the
trajectory in the photon-index and flux plane evolves clockwise or
counter-clockwise depending on the value of E and observed energy bands.Comment: 35 pages, 18 figures, accepted by the Astrophysical Journa
Coulomb blockade of tunnelling through compressible rings formed around an antidot: an explanation for Aharonov-Bohm oscillations
We consider single-electron tunnelling through antidot states using a
Coulomb-blockade model, and give an explanation for h/2e Aharonov-Bohm
oscillations, which are observed experimentally when the two spins of the
lowest Landau level form bound states. We show that the edge channels may
contain compressible regions, and using simple electrostatics, that the
resonance through the outer spin states should occur twice per h/e period. An
antidot may be a powerful tool for investigating quantum Hall edge states in
general, and the interplay of spin and charging effects that occurs in quantum
dots.Comment: 5 pages, 4 Postscript figure
ALMA polarimetric studies of rotating jet/disk systems
We have recently obtained polarimetric data at mm wavelengths with ALMA for
the young systems DG Tau and CW Tau, for which the rotation properties of jet
and disk have been investigated in previous high angular resolution studies.
The motivation was to test the models of magneto-centrifugal launch of jets via
the determination of the magnetic configuration at the disk surface. The
analysis of these data, however, reveals that self-scattering of dust thermal
radiation dominates the polarization pattern. It is shown that even if no
information on the magnetic field can be derived in this case, the polarization
data are a powerful tool for the diagnostics of the properties and the
evolution of dust in protoplanetary disks.Comment: 9 pages, 3 figures, to appear in "Jet Simulations, Experiments and
Theory. Ten years after JETSET, what is next ?", C. Sauty ed., Springer
Natur
Surface-acoustic-wave-driven luminescence from a lateral p-n junction
The authors report surface-acoustic-wave-driven luminescence from a lateral
p-n junction formed by molecular beam epitaxy regrowth of a modulation doped
GaAs/AlGaAs quantum well on a patterned GaAs substrate.
Surface-acoustic-wave-driven transport is demonstrated by peaks in the
electrical current and light emission from the GaAs quantum well at the
resonant frequency of the transducer. This type of junction offers high carrier
mobility and scalability. The demonstration of surface-acoustic-wave
luminescence is a significant step towards single-photon applications in
quantum computation and quantum cryptography.Comment: 4 pages, 3 figure
Stabilization of single-electron pumps by high magnetic fields
We study the effect of perpendicular magnetic fields on a single-electron
system with a strongly time-dependent electrostatic potential. Continuous
improvements to the current quantization in these electron pumps are revealed
by high-resolution measurements. Simulations show that the sensitivity of
tunnel rates to the barrier potential is enhanced, stabilizing particular
charge states. Nonadiabatic excitations are also suppressed due to a reduced
sensitivity of the Fock-Darwin states to electrostatic potential. The
combination of these effects leads to significantly more accurate current
quantization
Kiloparsec-Scale Jets in FR I Radio Galaxies and the Gamma-Ray Background
We discuss the contribution of kiloparsec-scale jets in FR I radio galaxies
to the diffuse gamma-ray background radiation. The analyzed gamma-ray emission
comes from inverse-Compton scattering of starlight photon fields by the
ultrarelativistic electrons whose synchrotron radiation is detected from such
sources at radio, optical and X-ray energies. We find that these objects, under
the minimum-power hypothesis (corresponding to a magnetic field of 300 muG in
the brightest knots of these jets), can contribute about one percent to the
extragalactic gamma-ray background measured by EGRET. We point out that this
result already indicates that the magnetic fields in kpc-scale jets of
low-power radio galaxies are not likely to be smaller than 10 muG on average,
as otherwise the extragalactic gamma-ray background would be overproduced.Comment: 18 pages, 3 figures included. ApJ accepte
Templeting of Thin Films Induced by Dewetting on Patterned Surfaces
The instability, dynamics and morphological transitions of patterns in thin
liquid films on periodic striped surfaces (consisting of alternating less and
more wettable stripes) are investigated based on 3-D nonlinear simulations that
account for the inter-site hydrodynamic and surface-energetic interactions. The
film breakup is suppressed on some potentially destabilizing nonwettable sites
when their spacing is below a characteristic lengthscale of the instability,
the upper bound for which is close to the spinodal lengthscale. The thin film
pattern replicates the substrate surface energy pattern closely only when, (a)
the periodicity of substrate pattern matches closely with the characteristic
lengthscale, and (b) the stripe-width is within a range bounded by a lower
critical length, below which no heterogeneous rupture occurs, and an upper
transition length above which complex morphological features bearing little
resemblance to the substrate pattern are formed.Comment: 5 pages TeX (REVTeX 4), other comments: submitted to Phys. Rev.Let
Chandra Discovery of an X-ray Jet and Lobes in 3C 15
We report the Chandra detection of an X-ray jet in 3C 15. The peak of the
X-ray emission in the jet is 4.1'' (a projected distance of 5.1 kpc) from the
nucleus, and coincident with a component previously identified in the radio and
optical jets. We examine four models for the X-ray jet emission: (I) weak
synchrotron cooling in equip., (II) moderate synchrotron cooling in equip.,
(III) weak synchrotron plus SSC cooling, and (IV) moderate synchrotron plus SSC
cooling. We argue that case (II) can most reasonably explain the overall
emission from knot C. Case (III) is also possible, but requires a large
departure from equipartition and for the jet power to be comparable to that of
the brightest quasars. Diffuse X-ray emission has also been detected,
distributed widely over the full extent (63kpc x 25kpc) of the radio lobes. We
compare the total energy contained in the lobes with the jet power estimated
from knot C, and discuss the energetic link between the jet and the lobes. We
argue that the fueling time (t_fuel) and the source age (t_src) are comparable
for case (II), whereas t_fuel << t_src is likely for case (III). The latter may
imply that the jet has a very small filling factor, ~10^{-3}. We consider the
pressure balance between the thermal galaxy halo and non-thermal relativistic
electrons in the radio lobes. Finally, we show that the X-ray emission from the
nucleus is not adequately fitted by a simple absorbed power-law model, but
needs an additional power-law with heavy absorption intrinsic to the source.
Such a high column density is consistent with the presence of a dense, dusty
torus which obscures the quasar nucleus.Comment: 14 pages, 8 figures, accepted for publication in A&
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