8,369 research outputs found
Comment on "Absence of Compressible Edge Channel Rings in Quantum Antidots"
In a recent article, Karakurt et al. [I. Karakurt et al., Phys. Rev. Lett.
89, 226803 (2002)] reported the absence of compressible regions around antidots
in the quantum Hall regime. We wish to point out a significant flaw in their
analysis, which invalidates their claim.Comment: 1 page 1 figure, to be published in Phys. Rev. Let
Kondo Effect in a Quantum Antidot
We report Kondo-like behaviour in a quantum antidot (a submicron depleted
region in a two-dimensional electron gas) in the quantum-Hall regime. When both
spin branches of the lowest Landau level encircle the antidot in a magnetic
field ( T), extra resonances occur between extended edge states via
antidot bound states when tunnelling is Coulomb blockaded. These resonances
appear only in alternating Coulomb-blockaded regions, and become suppressed
when the temperature or source-drain bias is raised. Although the exact
mechanism is unknown, we believe that Kondo-like correlated tunnelling arises
from skyrmion-type edge reconstruction. This observation demonstrates the
generality of the Kondo phenomenon.Comment: 9 pages, 3 figures (Fig.3 in colour), to appear in Phys. Rev. Let
Dynamics and High Energy Emission of the Flaring HST-1 Knot in the M 87 Jet
Stimulated by recent observations of a radio-to-X-ray synchrotron flare from
HST-1, the innermost knot of the M 87 jet, as well as by a detection of a very
high energy gamma-ray emission from M 87, we investigated the dynamics and
multiwavelength emission of the HST-1 region. We study thermal pressure of the
hot interstellar medium in M 87 and argue for a presence of a gaseous
condensation in its central parts. Interaction of the jet with such a feature
is likely to result in formation of a converging reconfinement shock in the
innermost parts of the M 87 jet. We show that for a realistic set of the
outflow parameters, a stationary and a flaring part of the HST-1 knot located
\~100 pc away from the active center can be associated with the decelerated
portion of the jet matter placed immediately downstream of the point where the
reconfinement shock reaches the jet axis. We discuss a possible scenario
explaining a broad-band brightening of the HST-1 region related to the variable
activity of the central core. We show that assuming a previous epoch of the
high central black hole activity resulting in ejection of excess particles and
photons down along the jet, one may first expect a high-energy flare of HST-1
due to inverse-Comptonisation of the nuclear radiation, followed after a few
years by an increase in the synchrotron continuum of this region. If this is
the case, then the recently observed increase in the knot luminosity in all
spectral bands could be regarded as an unusual echo of the outburst that had
happened previously in the active core of the M 87 radio galaxy.Comment: 30 pages, 7 figures included. Accepted for publication in MNRA
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
Galactic-Center Hyper-Shell Model for the North Polar Spurs
The bipolar-hyper shell (BHS) model for the North Polar Spurs (NPS-E, -W, and
Loop I) and counter southern spurs (SPS-E and -W) is revisited based on
numerical hydrodynamical simulations. Propagations of shock waves produced by
energetic explosive events in the Galactic Center are examined. Distributions
of soft X-ray brightness on the sky at 0.25, 0.7, and 1.5 keV in a +/-50 deg x
+/-50 deg region around the Galactic Center are modeled by thermal emission
from high-temperature plasma in the shock-compressed shell considering
shadowing by the interstellar HI and H2 gases. The result is compared with the
ROSAT wide field X-ray images in R2, 4 and 6 bands. The NPS and southern spurs
are well reproduced by the simulation as shadowed dumbbell-shaped shock waves.
We discuss the origin and energetics of the event in relation to the starburst
and/or AGN activities in the Galactic Center. [ High resolution pdf is
available at http://www.ioa.s.u-tokyo.ac.jp/~sofue/htdocs/2016bhs/ ]Comment: 13 pages, 20 figures; To appear in MNRA
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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