21,196 research outputs found
Very Rapid High-Amplitude Gamma-ray Variability in Luminous Blazar PKS 1510-089 Studied with Fermi-LAT
Here we report on the detailed analysis of the gamma-ray light curve of a
luminous blazar PKS1510-089 observed in the GeV range with the Large Area
Telescope (LAT) onboard the Fermi satellite during the period 2011 September --
December. By investigating the properties of the detected three major flares
with the shortest possible time binning allowed by the photon statistics, we
find a variety of temporal characteristics and variability patterns. This
includes a clearly asymmetric profile (with a faster flux rise and a slower
decay) of the flare resolved on sub-daily timescales, a superposition of many
short uncorrelated flaring events forming the apparently coherent
longer-duration outburst, and a huge single isolated outburst unresolved down
to the timescale of three-hours. In the latter case we estimate the
corresponding gamma-ray flux doubling timescale to be below one hour, which is
extreme and never previously reported for any active galaxy in the GeV range.
The other unique finding is that the total power released during the studied
rapid and high-amplitude flares constitute the bulk of the power radiatively
dissipated in the source, and a significant fraction of the total kinetic
luminosity of the underlying relativistic outflow. Our analysis allows us to
access directly the characteristic timescales involved in shaping the energy
dissipation processes in the source, and to provide constraints on the location
and the structure of the blazar emission zone in PKS1510-089.Comment: 15 pages, 4 figures, 1 table. Accepted for publication in the
Astrophysical Journal Letter
Intersubband Edge Singularity in Metallic Nanotubes
Tunneling density of states of both the massless and massive (gapped)
particles in metallic carbon nanotubes is known to have anomalous energy
dependence. This is the result of coupling to multiple low-energy bosonic
excitation (plasmons). For both kinds of particles the ensuing effect is the
suppression of the density of states by electron-electron interactions. We
demonstrate that the optical absorption between gapless and gapped states is
affected by the many-body effects in the opposite way. The absorption
probability is enhanced compared with the non-interacting value and develops a
power-law frequency dependence with the exponent -0.2 for typical nanotubes.Comment: 4 pages, 1 figure (final version, discussion of Sommerfeld factor and
Ref. 11 added
Characteristic energies, transition temperatures, and switching effects in clean SNS graphene nanostructures
We study proximity effects in clean nanoscale superconductor-normal
metal-superconductor (SNS) graphene heterostructures using a
self-consistent numerical solution to the continuum Dirac Bogoliubov-de Gennes
(DBdG) equations. We obtain results for the pair amplitude and the local
density of states (DOS), as a function of doping and of the geometrical
parameters determining the width of the structures. The superconducting
correlations are found to penetrate the normal graphene layers even when there
is extreme mismatch in the normal and superconducting doping levels, where
specular Andreev reflection dominates. The local DOS exhibits peculiar
features, which we discuss, arising from the Dirac cone dispersion relation and
from the interplay between the superconducting and Thouless energy scales. The
corresponding characteristic energies emerge in the form of resonant peaks in
the local DOS, that depend strongly on the doping level, as does the energy
gap, which declines sharply as the relative difference in doping between the S
and N regions is reduced. We also linearize the DBdG equations and develop an
essentially analytical method that determines the critical temperature of
an \sns nanostructure self-consistently. We find that for S regions that occupy
a fraction of the coherence length, can undergo substantial variations as
a function of the relative doping. At finite temperatures and by manipulating
the doping levels, the self consistent pair amplitudes reveal dramatic
transitions between a superconducting and resistive normal state of the
structure. Such behavior suggests the possibility of using the proposed system
as a carbon-based superconducting switch, turning superconductivity on or off
by tuning the relative doping levels.Comment: 13 pages, figures include
Variations of Hadron Masses and Matter Properties in Dense Nuclear Matter
Using a self-consistent quark model for nuclear matter we investigate
variations of the masses of the non-strange vector mesons, the hyperons and the
nucleon in dense nuclear matter (up to four times the normal nuclear density).
We find that the changes in the hadron masses can be described in terms of the
value of the scalar mean-field in matter. The model is then used to calculate
the density dependence of the quark condensate in-medium, which turns out to be
well approximated by a linear function of the nuclear density. Some relations
among the hadron properties and the in-medium quark condensate are discussed.Comment: 22 pages, University of Adelaide preperint ADP-94-20/T160, submitted
to Physical Review
Transport in the XX chain at zero temperature: Emergence of flat magnetization profiles
We study the connection between magnetization transport and magnetization
profiles in zero-temperature XX chains. The time evolution of the transverse
magnetization, m(x,t), is calculated using an inhomogeneous initial state that
is the ground state at fixed magnetization but with m reversed from -m_0 for
x0. In the long-time limit, the magnetization evolves into a
scaling form m(x,t)=P(x/t) and the profile develops a flat part (m=P=0) in the
|x/t|1/2 while it
expands with the maximum velocity, c_0=1, for m_0->0. The states emerging in
the scaling limit are compared to those of a homogeneous system where the same
magnetization current is driven by a bulk field, and we find that the
expectation values of various quantities (energy, occupation number in the
fermionic representation) agree in the two systems.Comment: RevTex, 8 pages, 3 ps figure
Maximal multihomogeneity of algebraic hypersurface singularities
From the degree zero part of logarithmic vector fields along an algebraic
hypersurface singularity we indentify the maximal multihomogeneity of a
defining equation in form of a maximal algebraic torus in the embedded
automorphism group. We show that all such maximal tori are conjugate and in
one-to-one correspondence to maxmimal tori in the degree zero jet of the
embedded automorphism group.
The result is motivated by Kyoji Saito's characterization of quasihomogeneity
for isolated hypersurface singularities and extends its formal version and a
result of Hauser and Mueller.Comment: 5 page
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