2,121 research outputs found
Parsec-Scale Bipolar X-ray Shocks Produced by Powerful Jets from the Neutron Star Circinus X-1
We report the discovery of multi-scale X-ray jets from the accreting neutron
star X-ray binary, Circinus X-1. The bipolar outflows show wide opening angles
and are spatially coincident with the radio jets seen in new high-resolution
radio images of the region. The morphology of the emission regions suggests
that the jets from Circinus X-1 are running into a terminal shock with the
interstellar medium, as is seen in powerful radio galaxies. This and other
observations indicate that the jets have a wide opening angle, suggesting that
the jets are either not very well collimated or precessing. We interpret the
spectra from the shocks as cooled synchrotron emission and derive a cooling age
of approximately 1600 yr. This allows us to constrain the jet power to be
between 3e35 erg/s and 2e37 erg/s, making this one of a few microquasars with a
direct measurement of its jet power and the only known microquasar that
exhibits stationary large-scale X-ray emission.Comment: 5 pages, 4 figures, to be published in the Astrophysical Journal
Letter
Ultrahigh Bandwidth Spin Noise Spectroscopy: Detection of Large g-Factor Fluctuations in Highly n-Doped GaAs
We advance all optical spin noise spectroscopy (SNS) in semiconductors to
detection bandwidths of several hundred gigahertz by employing an ingenious
scheme of pulse trains from ultrafast laser oscillators as an optical probe.
The ultrafast SNS technique avoids the need for optical pumping and enables
nearly perturbation free measurements of extremely short spin dephasing times.
We employ the technique to highly n-doped bulk GaAs where magnetic field
dependent measurements show unexpected large g-factor fluctuations.
Calculations suggest that such large g-factor fluctuations do not necessarily
result from extrinsic sample variations but are intrinsically present in every
doped semiconductor due to the stochastic nature of the dopant distribution.Comment: 5 pages, 3 figure
Shell-Shocked: The Interstellar Medium Near Cygnus X-1
We conduct a detailed case-study of the interstellar shell near the high-mass
X-ray binary, Cygnus X-1. We present new WIYN optical spectroscopic and Chandra
X-ray observations of this region, which we compare with detailed MAPPINGS III
shock models, to investigate the outflow powering the shell. Our analysis
places improved, physically motivated constraints on the nature of the
shockwave and the interstellar medium (ISM) it is plowing through. We find that
the shock is traveling at less than a few hundred km/s through a low-density
ISM (< 5 cm^-3). We calculate a robust, 3 sigma upper limit to the total,
time-averaged power needed to drive the shockwave and inflate the bubble, < 2 x
10^38 erg/s. We then review possible origins of the shockwave. We find that a
supernova origin to the shockwave is unlikely and that the black hole jet
and/or O-star wind can both be central drivers of the shockwave. We conclude
that the source of the Cygnus X-1 shockwave is far from solved.Comment: 16 pages, 8 figures, accepted for publication in MNRA
The Excitation of Extended Red Emission: New Constraints on its Carrier From HST Observations of NGC 7023
The carrier of the dust-associated photoluminescence process causing the
extended red emission (ERE) in many dusty interstellar environments remains
unidentified. Several competing models are more or less able to match the
observed broad, unstructured ERE band. We now constrain the character of the
ERE carrier further by determining the wavelengths of the radiation that
initiates the ERE. Using the imaging capabilities of the Hubble Space
Telescope, we have resolved the width of narrow ERE filaments appearing on the
surfaces of externally illuminated molecular clouds in the bright reflection
nebula NGC 7023 and compared them with the depth of penetration of radiation of
known wavelengths into the same cloud surfaces. We identify photons with
wavelengths shortward of 118 nm as the source of ERE initiation, not to be
confused with ERE excitation, however. There are strong indications from the
well-studied ERE in the Red Rectangle nebula and in the high-|b| Galactic
cirrus that the photon flux with wavelengths shortward of 118 nm is too small
to actually excite the observed ERE, even with 100% quantum efficiency. We
conclude, therefore, that ERE excitation results from a two-step process. While
none of the previously proposed ERE models can match these new constraints, we
note that under interstellar conditions most polycyclic aromatic hydrocarbon
(PAH) molecules are ionized to the di-cation stage by photons with E > 10.5 eV
and that the electronic energy level structure of PAH di-cations is consistent
with fluorescence in the wavelength band of the ERE. Therefore, PAH di-cations
deserve further study as potential carriers of the ERE. (abridged)Comment: Accepted for Publication in the Ap
For richer or poorer in sickness for wealth: what price consumerism?
Affluence and material goods of varying types are portents of a millennium age consumer culture that encourages the masses to voluntarily participate in the need to buy, buy and buy! This trend to spend creates a purchasing fervour that preoccupies many consumers with the ongoing yearning to shop until they drop. Clever marketing tactics such as enticing smells, catchy jingles, prize-draw entries, lucrative sales, discounts and the recruitment of celebrities to advertise a range of different wares are just some of the ploys adopted by vendors and retailers to maintain the sustainability of this cycle of consumer spending. This scenario promotes what could be perceived as a never-ending desire to procure yet more products and merchandise, which can create social dilemmas such as personal debt due to, for example, impulse buying, excessive spending and unnecessary borrowing.
Retailers and manufacturers are driven by a quest to sell so constantly tout their goods to tempt consumers including those with a need for personal and social respect, to take the bait in order to encourage them to keep buying. This, coupled with the rapid advances in technology over recent decades, has made it easier for consumers to shop, order, obtain and pay for their goods from the comfort of an armchair or via handheld devices, and all at a tap of a button. In essence, technology has added to, or even exacerbated, the materialistic consumer trend as witnessed across many global societies today – from the east and the west to the north and the south. But what impact does consumerism have on the well-being of humankind and, in turn, the environment? This chapter adopts a comparative approach to answer this question by exploring the implications of consumerism as a means for broadening the topic’s framework and to contribute to debates regarding consumerism, well-being, social dilemma, sustainability and techno-economics
Anomalous diffusion in polymers: long-time behaviour
We study the Dirichlet boundary value problem for viscoelastic diffusion in
polymers. We show that its weak solutions generate a dissipative semiflow. We
construct the minimal trajectory attractor and the global attractor for this
problem.Comment: 13 page
Observation and resonant x-ray optical interpretation of multi-atom resonant photoemission effects in O 1s emission from NiO
We present experimental and theoretical results for the variation of the O 1s
intensity from a NiO(001) surface as the excitation energy is varied through
the Ni 2p1/2,3/2 absorption resonances, and as the incidence angle of the
radiation is varied from grazing to larger values. For grazing incidence, a
strong multi-atom resonant photoemission (MARPE) effect is seen on the O 1s
intensity as the Ni 2p resonances are crossed, but its magnitude decreases
rapidly as the incidence angle is increased. Resonant x-ray optical (RXRO)
calculations are found to predict these effects very well, although the
experimental effects are found to decrease at higher incidence angles faster
than those in theory. The potential influence of photoelectron diffraction
effects on such measurements are also considered, including experimental data
with azimuthal-angle variation and corresponding
multiple-scattering-diffraction calculations, but we conclude that they do not
vary beyond what is expected on the basis of the change in photoelectron
kinetic energy. Varying from linear polarization to circular polarization is
found to enhance these effects in NiO considerably, although the reasons are
not clear. We also discuss the relationship of these measurements to other
related interatomic resonance experiments and theoretical developments, and
make some suggestions for future studies in this area.Comment: Phys. Rev. B, in pres
Polariton propagation in weak confinement quantum wells
Exciton-polariton propagation in a quantum well, under centre-of-mass
quantization, is computed by a variational self-consistent microscopic theory.
The Wannier exciton envelope functions basis set is given by the simple
analytical model of ref. [1], based on pure states of the centre-of-mass wave
vector, free from fitting parameters and "ad hoc" (the so called additional
boundary conditions-ABCs) assumptions. In the present paper, the former
analytical model is implemented in order to reproduce the centre-of-mass
quantization in a large range of quantum well thicknesses (5a_B < L < inf.).
The role of the dynamical transition layer at the well/barrier interfaces is
discussed at variance of the classical Pekar's dead-layer and ABCs. The Wannier
exciton eigenstates are computed, and compared with various theoretical models
with different degrees of accuracy. Exciton-polariton transmission spectra in
large quantum wells (L>> a_B) are computed and compared with experimental
results of Schneider et al.\cite{Schneider} in high quality GaAs samples. The
sound agreement between theory and experiment allows to unambiguously assign
the exciton-polariton dips of the transmission spectrum to the pure states of
the Wannier exciton center-of-mass quantization.Comment: 15 pages, 15 figures; will appear in Phys.Rev.
- …