12,097 research outputs found
Chandra and HST Confirmation of the Luminous and Variable X-ray Source IC 10 X-1 as a Possible Wolf-Rayet, Black-Hole Binary
We present a Chandra and HST study of IC 10 X-1, the most luminous X-ray
binary in the closest starburst galaxy to the Milky Way. Our new hard X-ray
observation of X-1 confirms that it has an average 0.5-10 keV luminosity of
1.5e38 erg/s, is strongly variable (a factor of ~2 in >3 ks), and is spatially
coincident (within 0.'23 +/-0.'30) with the Wolf-Rayet (WR) star [MAC92] 17A in
IC 10. The spectrum of X-1 is best fit by a power law with photon index of ~1.8
and a thermal plasma with kT~1.5 keV, although systematic residuals hint at
further complexity. Taken together, these facts suggest that X-1 may be a black
hole belonging to the rare class of WR binaries; it is comparable in many ways
to Cyg X-3. The Chandra observation also finds evidence for extended X-ray
emission co-spatial with the large non-thermal radio superbubble surrounding
X-1.Comment: ApJL in press (Oct 2003), 4 pages, 4 figures (w/ fig1 at severely
reduced quality), latest emulateapj.cls use
Small-scale swirl events in the quiet Sun chromosphere
Recent progress in instrumentation enables solar observations with high
resolution simultaneously in the spatial, temporal, and spectral domains. We
use such high-resolution observations to study small-scale structures and
dynamics in the chromosphere of the quiet Sun. We analyze time series of
spectral scans through the Ca II 854.2nm spectral line obtained with the CRISP
instrument at the Swedish 1-m Solar Telescope. The targets are quiet Sun
regions inside coronal holes close to disc-centre. The line core maps exhibit
relatively few fibrils compared to what is normally observed in quiet Sun
regions outside coronal holes. The time series show a chaotic and dynamic scene
that includes spatially confined "swirl" events. These events feature dark and
bright rotating patches, which can consist of arcs, spiral arms, rings or ring
fragments. The width of the fragments typically appears to be on the order of
only 0.2", which is close to the effective spatial resolution. They exhibit
Doppler shifts of -2 to -4 km/s but sometimes up to -7 km/s, indicating fast
upflows. The diameter of a swirl is usually of the order of 2". At the location
of these swirls, the line wing and wide-band maps show close groups of
photospheric bright points that move with respect to each other. A likely
explanation is that the relative motion of the bright points twists the
associated magnetic field in the chromosphere above. Plasma or propagating
waves may then spiral upwards guided by the magnetic flux structure, thereby
producing the observed intensity signature of Doppler-shifted ring fragments.Comment: 4 pages, 3 figures, A&A Letter, accepted (final version
Phase separation and the segregation principle in the infinite-U spinless Falicov-Kimball model
The simplest statistical-mechanical model of crystalline formation (or alloy
formation) that includes electronic degrees of freedom is solved exactly in the
limit of large spatial dimensions and infinite interaction strength. The
solutions contain both second-order phase transitions and first-order phase
transitions (that involve phase-separation or segregation) which are likely to
illustrate the basic physics behind the static charge-stripe ordering in
cuprate systems. In addition, we find the spinodal-decomposition temperature
satisfies an approximate scaling law.Comment: 19 pages and 10 figure
N=2 SYM Action as a BRST Exact Term, Topological Yang Mills and Instantons
By constructing a nilpotent extended BRST operator \bs that involves the
N=2 global supersymmetry transformations of one chirality, we show that the
standard N=2 off-shell Super Yang Mills Action can be represented as an exact
BRST term \bs \Psi, if the gauge fermion is allowed to depend on the
inverse powers of supersymmetry ghosts. By using this nonanalytical structure
of the gauge fermion (via inverse powers of supersymmetry ghosts), we give
field redefinitions in terms of composite fields of supersymmetry ghosts and
N=2 fields and we show that Witten's topological Yang Mills theory can be
obtained from the ordinary Euclidean N=2 Super Yang Mills theory directly by
using such field redefinitions. In other words, TYM theory is obtained as a
change of variables (without twisting). As a consequence it is found that
physical and topological interpretations of N=2 SYM are intertwined together
due to the requirement of analyticity of global SUSY ghosts. Moreover, when
after an instanton inspired truncation of the model is used, we show that the
given field redefinitions yield the Baulieu-Singer formulation of Topological
Yang Mills.Comment: Latex, 1+15 pages. Published versio
Classical transport equation in non-commutative QED at high temperature
We show that the high temperature behavior of non-commutative QED may be
simply obtained from Boltzmann transport equations for classical particles. The
transport equation for the charge neutral particle is shown to be
characteristically different from that for the charged particle. These
equations correctly generate, for arbitrary values of the non-commutative
parameter theta, the leading, gauge independent hard thermal loops, arising
from the fermion and the gauge sectors. We briefly discuss the generating
functional of hard thermal amplitudes.Comment: 11 page
Long-range nonlocal flow of vortices in narrow superconducting channels
We report a new nonlocal effect in vortex matter, where an electric current
confined to a small region of a long and sufficiently narrow superconducting
wire causes vortex flow at distances hundreds of inter-vortex separations away.
The observed remote traffic of vortices is attributed to a very efficient
transfer of a local strain through the one-dimensional vortex lattice, even in
the presence of disorder. We also observe mesoscopic fluctuations in the
nonlocal vortex flow, which arise due to "traffic jams" when vortex
arrangements do not match a local geometry of a superconducting channel.Comment: a slightly longer version of a tentatively accepted PR
Response of thin-film SQUIDs to applied fields and vortex fields: Linear SQUIDs
In this paper we analyze the properties of a dc SQUID when the London
penetration depth \lambda is larger than the superconducting film thickness d.
We present equations that govern the static behavior for arbitrary values of
\Lambda = \lambda^2/d relative to the linear dimensions of the SQUID. The
SQUID's critical current I_c depends upon the effective flux \Phi, the magnetic
flux through a contour surrounding the central hole plus a term proportional to
the line integral of the current density around this contour. While it is well
known that the SQUID inductance depends upon \Lambda, we show here that the
focusing of magnetic flux from applied fields and vortex-generated fields into
the central hole of the SQUID also depends upon \Lambda. We apply this
formalism to the simplest case of a linear SQUID of width 2w, consisting of a
coplanar pair of long superconducting strips of separation 2a, connected by two
small Josephson junctions to a superconducting current-input lead at one end
and by a superconducting lead at the other end. The central region of this
SQUID shares many properties with a superconducting coplanar stripline. We
calculate magnetic-field and current-density profiles, the inductance
(including both geometric and kinetic inductances), magnetic moments, and the
effective area as a function of \Lambda/w and a/w.Comment: 18 pages, 20 figures, revised for Phys. Rev. B, the main revisions
being to denote the effective flux by \Phi rather than
Charge-transfer metal-insulator transitions in the spin-one-half Falicov-Kimball model
The spin-one-half Falicov-Kimball model is solved exactly on an
infinite-coordination-number Bethe lattice in the thermodynamic limit. This
model is a paradigm for a charge-transfer metal-insulator transition where the
occupancy of localized and delocalized electronic orbitals rapidly changes at
the metal-insulator transition (rather than the character of the electronic
states changing from insulating to metallic as in a Mott-Hubbard transition).
The exact solution displays both continuous and discontinuous (first-order)
transitions.Comment: 22 pages including 4 figures(eps), RevTe
Direct perturbation theory on the shift of Electron Spin Resonance
We formulate a direct and systematic perturbation theory on the shift of the
main paramagnetic peak in Electron Spin Resonance, and derive a general
expression up to second order. It is applied to one-dimensional XXZ and
transverse Ising models in the high field limit, to obtain explicit results
including the polarization dependence for arbitrary temperature.Comment: 5 pages (no figures) in REVTE
- …