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 ($\sim 1$ 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

Phonon emission and arrival times of electrons from a single-electron source

In recent charge-pump experiments, single electrons are injected into quantum Hall edge channels at energies significantly above the Fermi level. We consider here the relaxation of these hot edge-channel electrons through longitudinal-optical-phonon emission. Our results show that the probability for an electron in the outermost edge channel to emit one or more phonons en route to a detector some microns distant along the edge channel suffers a double-exponential suppression with increasing magnetic field. This explains recent experimental observations. We also describe how the shape of the arrival-time distribution of electrons at the detector reflects the velocities of the electronic states post phonon emission. We show how this can give rise to pronounced oscillations in the arrival-time-distribution width as a function of magnetic field or electron energy

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

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

Coulomb blockade of tunnelling through compressible rings formed around an antidot: an explanation for h/2eh/2e 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

A numerical code to study the variability of Blazar emission

We present a numerical code, written in C, which can be used to simulate or to analyze the emission of Blazars over the entire electromagnetic spectrum. Our code can reproduce the following features: synchrotron emission, inverse Compton emission (Thomson Klein-Nishina regime) external Compton emission, accretion disk variability using a Cellular Automata algorithm, temporal evolution of the emitting plasma energy distribution, flaring phenomena, light curves in the rest and in the observer frame (taking account for time crossing effects). In this paper we will show mainly the accretion disk simulation, and the implications in the External Compton scenario.Comment: 4 pages, 2 eps figures. Poster to "The Physics of Relativistic Jets in the CHANDRA and XMM Era" (Bologna CNR). Proceedings to be published in New Astronomy Review

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&