20,866 research outputs found
Multi-wavelength Emission from the Fermi Bubble III. Stochastic (Fermi) Re-Acceleration of Relativistic Electrons Emitted by SNRs
We analyse the model of stochastic re-acceleration of electrons, which are
emitted by supernova remnants (SNRs) in the Galactic Disk and propagate then
into the Galactic halo, in order to explain the origin on nonthermal (radio and
gamma-ray) emission from the Fermi Bubbles (FB). We assume that the energy for
re-acceleration in the halo is supplied by shocks generated by processes of
star accretion onto the central black hole. Numerical simulations show that
regions with strong turbulence (places for electron re-acceleration) are
located high up in the Galactic Halo about several kpc above the disk. The
energy of SNR electrons that reach these regions does not exceed several GeV
because of synchrotron and inverse Compton energy losses. At appropriate
parameters of re-acceleration these electrons can be re-accelerated up to the
energy 10E12 eV which explains in this model the origin of the observed radio
and gamma-ray emission from the FB. However although the model gamma-ray
spectrum is consistent with the Fermi results, the model radio spectrum is
steeper than the observed by WMAP and Planck. If adiabatic losses due to plasma
outflow from the Galactic central regions are taken into account, then the
re-acceleration model nicely reproduces the Planck datapoints.Comment: 33 pages, 8 figures, accepted by Ap
Particle acceleration and the origin of gamma-ray emission from Fermi Bubbles
Fermi LAT has discovered two extended gamma-ray bubbles above and below the
galactic plane. We propose that their origin is due to the energy release in
the Galactic center (GC) as a result of quasi-periodic star accretion onto the
central black hole. Shocks generated by these processes propagate into the
Galactic halo and accelerate particles there. We show that electrons
accelerated up to ~10 TeV may be responsible for the observed gamma-ray
emission of the bubbles as a result of inverse Compton (IC) scattering on the
relic photons. We also suggest that the Bubble could generate the flux of CR
protons at energies > 10^15 eV because the shocks in the Bubble have much
larger length scales and longer lifetimes in comparison with those in SNRs.
This may explain the the CR spectrum above the knee.Comment: 5 pages, 4 figures. Expanded version of the contribution to the 32nd
ICRC, Beijing, #0589. To appear in the proceeding
Measurement Invariance of the Internet Addiction Test Among Hong Kong, Japanese, and Malaysian Adolescents
There has been increased research examining the psychometric properties on the Internet Addiction Test across different ages and populations. This population-based study examined the psychometric properties using Confirmatory Factory Analysis and measurement invariance using Item Response Theory (IRT) of the IAT in adolescents from three Asian countries. In the Asian Adolescent Risk Behavior Survey (AARBS), 2,535 secondary school students (55.91% girls) in Grade 7 to Grade 13 (Mean age = 15.61 years; SD=1.56) from Hong Kong (n=844), Japan (n=744), and Malaysia (n=947) completed a survey on their Internet use that incorporated the IAT scale. A nested hierarchy of hypotheses concerning IAT cross-country invariance was tested using multi-group confirmatory factor analysis. Replicating past finding in Hong Kong adolescents, the construct of IAT is best represented by a second-order three-factor structure in Malaysian and Japanese adolescents. Configural, metric, scalar, and partial strict factorial invariance was established across the three samples. No cross-country differences on Internet addiction were detected at latent mean level. This study provided empirical support to the IAT as a reliable and factorially stable instrument, and valid to be used across Asian adolescent populations
Hadron widths in mixed-phase matter
We derive classically an expression for a hadron width in a two-phase region
of hadron gas and quark-gluon plasma (QGP). The presence of QGP gives hadrons
larger widths than they would have in a pure hadron gas. We find that the
width observed in a central Au+Au collision at
GeV/nucleon is a few MeV greater than the width in a pure hadron gas. The part
of observed hadron widths due to QGP is approximately proportional to
.Comment: 8 pages, latex, no figures, KSUCNR-002-9
Particle correlations at RHIC from parton coalescence dynamics -- first results
A new dynamical approach that combines covariant parton transport theory with
hadronization channels via parton coalescence and fragmentation is applied to
Au+Au at RHIC. Basic consequences of the simple coalescence formulas, such as
elliptic flow scaling and enhanced proton/pion ratio, turn out to be rather
sensitive to the spacetime aspects of coalescence dynamics.Comment: Contribution to Quark Matter 2004 (January 11-17, 2004, Oakland, CA).
4 pages, 2 EPS figs, IOP style fil
Kaon differential flow in relativistic heavy-ion collisions
Using a relativistic transport model, we study the azimuthal momentum
asymmetry of kaons with fixed transverse momentum, i.e., the differential flow,
in heavy-ion collisions at beam momentum of 6 GeV/c per nucleon, available from
the Alternating Gradient Synchrotron (AGS) at the Brookhaven National
Laboratory (BNL). We find that in the absence of kaon potential the kaon
differential flow is positive and increases with transverse momentum as that of
nucleons. The repulsive kaon potential as predicted by theoretical models,
however, reduces the kaon differetnial flow, changing it to negative for kaons
with low momenta. Cancellation between the negative differential flow at low
mementa and the positive one at high momenta is then responsible for the
experimentally observed nearly vanishing in-plane transverse flow of kaons in
heavy ion experiments.Comment: Phys. Rev. C in pres
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