557 research outputs found
Multidimensional relativistic MHD simulations of Pulsar Wind Nebulae: dynamics and emission
Full text linkPulsar Wind Nebulae, and the Crab nebula in particular, are the best cosmic
laboratories to investigate the dynamics of magnetized relativistic outflows
and particle acceleration up to PeV energies. Multidimensional MHD modeling by
means of numerical simulations has been very successful at reproducing, to the
very finest details, the innermost structure of these synchrotron emitting
nebulae, as observed in the X-rays. Therefore, the comparison between the
simulated source and observations can be used as a powerful diagnostic tool to
probe the physical conditions in pulsar winds, like their composition,
magnetization, and degree of anisotropy. However, in spite of the wealth of
observations and of the accuracy of current MHD models, the precise mechanisms
for magnetic field dissipation and for the acceleration of the non-thermal
emitting particles are mysteries still puzzling theorists to date. Here we
review the methodologies of the computational approach to the modeling of
Pulsar Wind Nebulae, discussing the most relevant results and the recent
progresses achieved in this fascinating field of high-energy astrophysics.Comment: 29 pages review, preliminary version. To appear in the book
"Modelling Nebulae" edited by D. Torres for Springer, based on the invited
contributions to the workshop held in Sant Cugat (Barcelona), June 14-17,
201
Particle Acceleration in Pulsar Wind Nebulae: PIC modelling
Full text linkWe discuss the role of particle-in-cell (PIC) simulations in unveiling the
origin of the emitting particles in PWNe. After describing the basics of the
PIC technique, we summarize its implications for the quiescent and the flaring
emission of the Crab Nebula, as a prototype of PWNe. A consensus seems to be
emerging that, in addition to the standard scenario of particle acceleration
via the Fermi process at the termination shock of the pulsar wind, magnetic
reconnection in the wind, at the termination shock and in the Nebula plays a
major role in powering the multi-wavelength signatures of PWNe.Comment: 32 pages, 16 figures, to appear in the book "Modelling Nebulae"
edited by D. Torres for Springer, based on the invited contributions to the
workshop held in Sant Cugat (Barcelona), June 14-17, 201
RS Indi: un sistema de contacto virtual con período orbital decreciente
Get PDFPhotoelectric UBV observations of the eclipsing binary RS Indi carried out at Cerro Tololo and Bosque Alegre have enabled us to obtain its light curves and to analyse in detail is orbital period. The determination of the ephemeris of the system allows us to confirm that its period diminished by 0.0185 secons per yea. On the other hand, the light curves are indicative of a highly distortioned system with therman decoupling. The general configuration of RS Indi is that of a system in virtual contact with possible mass transfer from the principal component to the secondary one.Asociación Argentina de Astronomí
Magnetoluminescence
Full text linkPulsar Wind Nebulae, Blazars, Gamma Ray Bursts and Magnetars all contain
regions where the electromagnetic energy density greatly exceeds the plasma
energy density. These sources exhibit dramatic flaring activity where the
electromagnetic energy distributed over large volumes, appears to be converted
efficiently into high energy particles and gamma-rays. We call this general
process magnetoluminescence. Global requirements on the underlying, extreme
particle acceleration processes are described and the likely importance of
relativistic beaming in enhancing the observed radiation from a flare is
emphasized. Recent research on fluid descriptions of unstable electromagnetic
configurations are summarized and progress on the associated kinetic
simulations that are needed to account for the acceleration and radiation is
discussed. Future observational, simulation and experimental opportunities are
briefly summarized.Comment: To appear in "Jets and Winds in Pulsar Wind Nebulae, Gamma-ray Bursts
and Blazars: Physics of Extreme Energy Release" of the Space Science Reviews
serie
238U(n, γ) reaction cross section measurement with C 6D6 detectors at the n-TOF CERN facility
Get PDFThis is an Open Access article distributed under the terms of the Creative Commons Attribution License 2.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly citedThe radiative capture cross section of 238U is very important for the developing of new reactor technologies and the safety of existing ones. Here the preliminary results of the 238U(n,γ) cross section measurement performed at n-TOF with C6D6 scintillation detectors are presented, paying particular attention to data reduction and background subtraction.Peer reviewe
The nucleosynthesis of heavy elements in Stars : The key isotope 25Mg
Get PDFThis is an Open Access article distributed under the terms of the Creative Commons Attribution License 2.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly citedWe have measured the radiative neutron-capture cross section and the total neutron-induced cross section of one of the most important isotopes for the s process, the 25Mg. The measurements have been carried out at the neutron time-of-flight facilities n-TOF at CERN (Switzerland) and GELINA installed at the EC-JRC-IRMM (Belgium). The cross sections as a function of neutron energy have been measured up to approximately 300 keV, covering the energy region of interest to the s process. The data analysis is ongoing and preliminary results show the potential relevance for the s process.Peer reviewe
Search for supersymmetry with a dominant R-parity violating LQDbar couplings in e+e- collisions at centre-of-mass energies of 130GeV to 172 GeV
Full text linkA search for pair-production of supersymmetric particles under the assumption
that R-parity is violated via a dominant LQDbar coupling has been performed
using the data collected by ALEPH at centre-of-mass energies of 130-172 GeV.
The observed candidate events in the data are in agreement with the Standard
Model expectation. This result is translated into lower limits on the masses of
charginos, neutralinos, sleptons, sneutrinos and squarks. For instance, for
m_0=500 GeV/c^2 and tan(beta)=sqrt(2) charginos with masses smaller than 81
GeV/c^2 and neutralinos with masses smaller than 29 GeV/c^2 are excluded at the
95% confidence level for any generation structure of the LQDbar coupling.Comment: 32 pages, 30 figure
Search for the glueball candidates f0(1500) and fJ(1710) in gamma gamma collisions
Full text linkData taken with the ALEPH detector at LEP1 have been used to search for gamma
gamma production of the glueball candidates f0(1500) and fJ(1710) via their
decay to pi+pi-. No signal is observed and upper limits to the product of gamma
gamma width and pi+pi- branching ratio of the f0(1500) and the fJ(1710) have
been measured to be Gamma_(gamma gamma -> f0(1500)). BR(f0(1500)->pi+pi-) <
0.31 keV and Gamma_(gamma gamma -> fJ(1710)). BR(fJ(1710)->pi+pi-) < 0.55 keV
at 95% confidence level.Comment: 10 pages, 3 figure
Pion freeze-out as seen through HBT correlations in heavy ion collisions from FAIR/AGS to RHIC energies
Get PDFWe perform a systematic analysis of several HBT parameters in heavy ion
collisions from AGeV to GeV within
the UrQMD transport approach and compare the results to experimental data where
available. We find that the 'lifetime' of the emission source as calculated
from , is larger than the experimentally
observed values at all investigated energies. The calculated volume of the pion
source () is found to increase monotonously with increasing beam energy
and the experimentally observed decrease of the measured at AGS is not
seen. Finally, we calculate the mean free path fm of pions at
freeze-out and find a good description of the experimental data above the AGS
energy region, supporting the suggestion of a universal kinetic decoupling
criterion up to the highest RHIC energies.Comment: 11 pages, 2 fig
Search for direct production of charginos and neutralinos in events with three leptons and missing transverse momentum in √s = 7 TeV pp collisions with the ATLAS detector
Get PDFA search for the direct production of charginos and neutralinos in final states with three electrons or muons and missing transverse momentum is presented. The analysis is based on 4.7 fb−1 of proton–proton collision data delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with Standard Model expectations in three signal regions that are either depleted or enriched in Z-boson decays. Upper limits at 95% confidence level are set in R-parity conserving phenomenological minimal supersymmetric models and in simplified models, significantly extending previous results
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