12,094 research outputs found
A model for jets of low-mass microquasars
In this work we present a new jet model for the non-thermal broadband
emission of low-mass microquasars. We calculate the contribution of
relativistic particles, primary electrons and protons as well as secondary
muons, charged pions and electron-positron pairs, to the electromagnetic
spectrum of the sources. The distribution in energy of all particle species is
obtained for an extended, inhomogeneous region. We include detailed analysis of
particle energy losses, injection, decay and escape from the acceleration zone.
We also calculate absorption effects due to photon-photon annihilation. As an
application, we consider the case of XTE J1118+480, a well-known low-mass X-ray
binary in the galactic halo, and we present predictions about its high-energy
radiationComment: 7 pages, 6 figures. Proceedings of the 25th Texas Symposium on
Relativistic Astrophysics - TEXAS 2010, December 06-10, 2010, Heidelberg,
German
Leptonic/hadronic models for electromagnetic emission in microquasars: the case of GX 339-4
We present a general self-consistent lepto/hadronic jet model for the
non-thermal electromagnetic emission of microquasars. The model is applied to
the low-mass microquasar (LMMQ) GX 339-4 and predicts its high-energy features.
We assume that both leptons and hadrons are accelerated up to relativistic
energies by diffusive shock acceleration, and calculate their contribution to
the electromagnetic spectrum through all main radiative processes. The
radiative contribution of secondary particles (pions, muons and
electron-positron pairs) is included. We use a set of simultaneous observations
in radio and X-rays to constrain the model parameters and find the best fit to
the data. We obtain different spectral energy distributions that can explain
the observations, and make predictions for the high-energy emission.
Observations with gamma-ray instruments like Fermi can be used to test the
model and determine the proton content of the jets. Finally, we estimate the
positron injection in the surrounding medium. Our findings support the
suggested association between LMMQs and the observed distribution of the 511
keV line flux observed by INTEGRAL.Comment: 13 pages, 7 figures, accepted for publication in MNRA
Thermal and Magnetic Quantum Discord in Heisenberg models
We investigate how the quantum correlations (quantum discord) of a two-qubit
one dimensional XYZ Heisenberg chain in thermal equilibrium depends on the
temperature (T) of the bath and also on an external magnetic field B. We show
that the behavior of the thermal quantum discord (QD) differs in many
unexpected ways from the thermal entanglement. For example, we show situations
where QD increases with T when entanglement decreases, cases where QD increases
with T even in regions with zero entanglement, and that QD signals a quantum
phase transition even at finite T. We also show that by properly tuning B or
the interaction between the qubits we get non-zero QD for any T and we present
a new effect not seen for entanglement, the regrowth of thermal QD.Comment: 4 pages, 5 figures, RevTex, double column; v2: published versio
A study of the two northern open clusters NGC 1582 and NGC 1663
We present CCD UBV(I)C observations obtained in the field of the previously unstudied northern open clusters NGC 1582 and NGC 1663. For the former, we also provide high-resolution spectra of the brightest stars and complement our data with Two-Micron All-Sky-Survey (2MASS) near-infrared photometry and with astrometric data from the Tycho-2 catalog. From the analysis of all these data, we argue that NGC 1582 is a very poor, quite large and heavily contaminated open cluster. It turns out to have a reddening EB-V = 0.35 +/- 0.03, to be situated 1100 +/- 100 pc from the Sun and to have an age of 300 +/- 100 Myr. On the other hand, we were not able to unambiguously clarify the nature of NGC 1663. By assuming it is a real cluster and from the analysis of its photometric diagrams, we found a color excess value EB-V = 0.20, an intermediate age value ( ~ 2000 Myr) and a distance of about 700 pc. The distribution of the stars in the region however suggests we are probably facing an open cluster remnant. As an additional result, we obtained aperture photometry of three previously unclassified galaxies placed in the field of NGC 1663 and performed a preliminary morphological classification of them.Fil: Baume, Gustavo Luis. Università di Padova; ItaliaFil: Villanova, S.. Università di Padova; Italia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica la Plata; ArgentinaFil: Carraro, Giovanni. Università di Padova; Itali
Local and Effective Temperatures of Quantum Driven Systems
We introduce thermometers to define the local temperature of an electronic
system driven out-of-equilibrium by local AC fields. We also define the
effective temperature in terms of a local fluctuation-dissipation-relation. We
show that within the weak driving regime these two temperatures coincide. We
also discuss the behavior of the local temperature along the sample. We show
that it exhibits spatial fluctuations following an oscillatory pattern. For
weak driving, regions of the sample become heated, while others become cooled
as a consequence of the driving
Hybrid confinement of optical and mechanical modes in a bullseye optomechanical resonator
Optomechanical cavities have proven to be an exceptional tool to explore
fundamental and technological aspects of the interaction between mechanical and
optical waves. Such interactions strongly benefit from cavities with large
optomechanical coupling, high mechanical and optical quality factors, and
mechanical frequencies larger than the optical mode linewidth, the so called
resolved sideband limit. Here we demonstrate a novel optomechanical cavity
based on a disk with a radial mechanical bandgap. This design confines light
and mechanical waves through distinct physical mechanisms which allows for
independent control of the mechanical and optical properties. Our device design
is not limited by unique material properties and could be easily adapted to
allow large optomechanical coupling and high mechanical quality factors with
other promising materials. Finally, our demonstration is based on devices
fabricated on a commercial silicon photonics facility, demonstrating that our
approach can be easily scalable.Comment: 16 pages, 11 figure
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