6,575 research outputs found
Microquasars: disk-jet coupling in stellar-mass black holes
Microquasars provide new insights into: 1) the physics of relativistic jets
from black holes, 2) the connection between accretion and ejection, and 3) the
physical mechanisms in the formation of stellar-mass black holes. Furthermore,
the studies of microquasars in our Galaxy can provide in the future new
insights on: 1) a large fraction of the ultraluminous X-ray sources in nearby
galaxies, 2) gamma-ray bursts (GRBs) of long duration in distant galaxies, and
3) the physics in the jets of blazars. If jets in GRBs, microquasars and Active
Galactic Nuclei (AGN) are due to a unique universal magnetohydrodynamic
mechanism, synergy of the research on these three different classes of cosmic
objects will lead to further progress in black hole physics and astrophysics.Comment: 4 pages, 3 figures. To appear in Proceedings of IAU Symp. No 238
"Black Holes: from Stars to Galaxies - across the Range of Masses. Held in
Prague, August 21-25, 2006. Eds. V. Karas & G. Mat
Exploiting quantum parallelism to simulate quantum random many-body systems
We present an algorithm that exploits quantum parallelism to simulate randomness in a quantum system. In our scheme, all possible realizations of the random parameters are encoded quantum mechanically in a superposition state of an auxiliary system. We show how our algorithm allows for the efficient simulation of dynamics of quantum random spin chains with known numerical methods. We propose an experimental realization based on atoms in optical lattices in which disorder could be simulated in parallel and in a controlled way through the interaction with another atomic species
Fermionic Atoms in Optical Superlattices
Fermionic atoms in an optical superlattice can realize a very peculiar
Anderson lattice model in which impurities interact with each other through a
discretized set of delocalized levels. We investigate the interplay between
Kondo effect and magnetism under these finite-size features. We find that Kondo
effect can dominate over magnetism depending on the parity of the number of
particles per discretized set. We show how Kondo-induced resonances of
measurable size can be observed through the atomic interference pattern
A possible black hole in the gamma-ray microquasar LS 5039
The population of high energy and very high energy gamma-ray sources,
detected with EGRET and the new generation of ground-based Cherenkov
telescopes, conforms a reduced but physically important sample. Most of these
sources are extragalactic (e.g., blazars), while among the galactic ones there
are pulsars and SN remnants. The microquasar LS 5039, previously proposed to be
associated with an EGRET source by Paredes et al. (2000), has recently been
detected at TeV energies, confirming that microquasars should be regarded as a
class of high energy gamma-ray sources. To model and understand how the
energetic photons are produced and escape from LS 5039 it is crucial to unveil
the nature of the compact object, which remains unknown. Here we present new
intermediate-dispersion spectroscopy of this source which, combined with values
reported in the literature, provides an orbital period of 3.90603+/-0.00017 d,
a mass function f(M)=0.0053+/-0.0009 M_sun, and an eccentricity e=0.35+/-0.04.
Atmosphere model fitting to the spectrum of the optical companion, together
with our new distance estimate of d=2.5+/-0.1 kpc, yields R_opt=9.3+0.7-0.6
R_sun, log (L_opt/L_sun)=5.26+/-0.06, and M_opt=22.9+3.4-2.9 M_sun. These,
combined with our dynamical solution and the assumption of
pseudo-synchronization, yield an inclination i=24.9+/-2.8 degree and a compact
object mass M_X=3.7+1.3-1.0 M_sun. This is above neutron star masses for most
of the standard equations of state and, therefore, we propose that the compact
object in LS 5039 is a black hole. We finally discuss about the implications of
our orbital solution and new parameters of the binary system on the CNO
products, the accretion/ejection energetic balance, the SN explosion scenario,
and the behaviour of the TeV emission with the new orbital period.Comment: 10 pages, 8 figures. Accepted for publication in MNRAS. Minor changes
according to referee repor
Experimental realization of plaquette resonating valence bond states with ultracold atoms in optical superlattices
The concept of valence bond resonance plays a fundamental role in the theory
of the chemical bond and is believed to lie at the heart of many-body quantum
physical phenomena. Here we show direct experimental evidence of a
time-resolved valence bond quantum resonance with ultracold bosonic atoms in an
optical lattice. By means of a superlattice structure we create a
three-dimensional array of independent four-site plaquettes, which we can fully
control and manipulate in parallel. Moreover, we show how small-scale plaquette
resonating valence bond states with s- and d-wave symmetry can be created and
characterized. We anticipate our findings to open the path towards the creation
and analysis of many-body RVB states in ultracold atomic gases.Comment: 7 page, 4 figures in main text, 3 figures in appendi
Pfaffian-like ground state for 3-body-hard-core bosons in 1D lattices
We propose a Pfaffian-like Ansatz for the ground state of bosons subject to
3-body infinite repulsive interactions in a 1D lattice. Our Ansatz consists of
the symmetrization over all possible ways of distributing the particles in two
identical Tonks-Girardeau gases. We support the quality of our Ansatz with
numerical calculations and propose an experimental scheme based on mixtures of
bosonic atoms and molecules in 1D optical lattices in which this Pfaffian-like
state could be realized. Our findings may open the way for the creation of
non-abelian anyons in 1D systems
Influence of quenched dilution on the quasi-long-range ordered phase of the 2d XY model
The influence of non magnetic impurities in the 2d XY model is investigated
through Monte Carlo (MC) simulations. The general picture of the transition is
fully understood from the Harris criterion which predicts that the universality
class is unchanged, and the Berezinskii-Kosterlitz-Thouless description of the
topological transition remains valid. We nevertheless address here the question
about the influence of dilution on the quasi-long-range order at low
temperatures. In particular, we study the asymptotic of the pair correlation
function and report the MC estimates for the critical exponent at
different dilutions. In the weak dilution region, our MC calculations are
further supported by simple spin-wave-like calculations.Comment: 8 pages, 7 eps figure
A Multiwavelength Investigation of the Relationship Between 2CG135+1 and LSI+61o 303
We present the results of a multiwavelength monitoring campaign targeting the
gamma-ray source 2CG 135+1 in an attempt to confirm the association of this
object with the radio/Be/X-ray binary system LSI +61o 303. The campaign
included simultaneous radio, optical, infrared, and hard x-ray/gamma-ray
observations carried out with a variety of instruments, covering (not
continously) almost three binary cycles of LSI +61o 303 during the period
April-July 1994. Three separate OSSE observations of the gamma-ray source were
carried out, covering different phases of the radio lightcurve. Hard
X-ray/gamma-ray emission was detected from the direction of 2CG 135+1 during
the first of these OSSE observations. The signal to noise ratio of the OSSE
observations was insufficient to establish a spectral or intensity correlation
of the high-energy emission with simultaneous radio, optical and infrared
emission of LSI +61o 303. We briefly discuss the theoretical implications of
our observations.Comment: 17 pages, 9 figures, 6 tables to be published in Astrophysical
Journal, 10 April 199
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