1,075 research outputs found
Magnetic Field Evolution in Merging Clusters of Galaxies
We present initial results from the first 3-dimensional numerical
magnetohydrodynamical (MHD) simulations of magnetic field evolution in merging
clusters of galaxies. Within the framework of idealized initial conditions
similar to our previous work, we look at the gasdynamics and the magnetic field
evolution during a major merger event in order to examine the suggestion that
shocks and turbulence generated during a cluster/subcluster merger can produce
magnetic field amplification and relativistic particle acceleration and, as
such, may play a role in the formation and evolution of cluster-wide radio
halos. The ICM, as represented by the equations of ideal MHD, is evolved
self-consistently within a changing gravitational potential defined largely by
the collisionless dark matter component represented by an N-body particle
distribution. The MHD equations are solved by the Eulerian, finite-difference
code, ZEUS. The particles are evolved by a standard particle-mesh (PM) code. We
find significant evolution of the magnetic field structure and strength during
two distinct epochs of the merger evolution.Comment: 21 pages, 7 figures, Figure 2 is color postscript. Accepted for
publication in Ap
The Energy Spectrum of Primary Cosmic Ray Electrons in Clusters of Galaxies and Inverse Compton Emission
Models for the evolution of the integrated energy spectrum of primary cosmic
ray electrons in clusters of galaxies have been calculated, including the
effects of losses due to inverse Compton (IC), synchrotron, and bremsstrahlung
emission, and Coulomb losses to the intracluster medium (ICM). The combined
time scale for these losses reaches a maximum of ~3e9 yr for electrons with a
Lorentz factor ~300. Only clusters in which there has been a substantial
injection of relativistic electrons since z <~ 1 will have any significant
population of primary cosmic ray electrons at present. In typical models, there
is a broad peak in the electron energy distribution extending to gamma~300, and
a steep drop in the electron population beyond this. In clusters with current
particle injection, there is a power-law tail of higher energy electrons with
an abundance determined by the current rate of injection. A significant
population of electrons with gamma~300, associated with the peak in the
particle loss time, is a generic feature of the models. The IC and synchrotron
emission from these models was calculated. In the models, EUV and soft X-ray
emission are nearly ubiquitous. This emission is produced by electrons with
gamma~300. The spectra are predicted to drop rapidly in going from the EUV to
the X-ray band. The IC emission also extends down the UV, optical, and IR bands
with a fairly flat spectrum. Hard X-ray (HXR) and diffuse radio emission due to
high energy electrons (gamma~10e4) is present only in clusters which have
current particle acceleration. Assuming that the electrons are accelerated in
ICM shocks, one would only expect diffuse HXR/radio emission in clusters which
are currently undergoing a large merger.Comment: Accepted for publication in the Astrophysical Journal, with minor
revisons to wording for clarity and one additional reference. 19 pages with
16 embedded Postscript figures in emulateapj.sty. Abbreviated abstract belo
Peripheral elastic and inelastic scattering of O 17 , 18 on light targets at 12 MeV/nucleon
A study of interaction of neutron rich oxygen isotopes O with light
targets has been undertaken in order to determine the optical potentials needed
for the transfer reaction C(O,O)C. Optical
potentials in both incoming and outgoing channels have been determined in a
single experiment. This transfer reaction was used to infer the direct capture
rate to the F(p,)Ne which is essential to estimate the
production of F at stellar energies in ONe novae. The success of the
asymptotic normalization coefficient (ANC) as indirect method for astrophysics
is guaranteed if the reaction mechanism is peripheral and the DWBA cross
section calculations are warranted and stable against OMP used. We demonstrate
the stability of the ANC method and OMP results using good quality elastic and
inelastic scattering data with stable beams before extending the procedures to
rare ion beams. The peripherality of our reaction is inferred from a
semiclassical decomposition of the total scattering amplitude into barrier and
internal barrier components.
Comparison between elastic scattering of O, O and O
projectiles is made.Comment: 14 pages, 19 figure
Scattering of Be and B and the astrophysical S factor
Measurements of scattering of Be at 87 MeV on a melamine (CNH) target and of B at 95 MeV on C were performed. For Be
the angular range was extended over previous measurements and monitoring of the
intensity of the radioactive beam was improved. The measurements allowed us to
check and improve the optical model potentials used in the incoming and
outgoing channels for the analysis of existing data on the proton transfer
reaction N(Be,B)C. The resultslead to an updated
determination of the asymptotic normalization coefficient for the virtual decay
B Be + . We find a slightly larger value,
fm, for the melamine target. This
implies an astrophysical factor, eVb, for the
solar neutrino generating reaction Be(,)B.Comment: 7 pages, 4 figure
Trojan Horse as an indirect technique in nuclear astrophysics. Resonance reactions
The Trojan Horse method is a powerful indirect technique that provides
information to determine astrophysical factors for binary rearrangement
processes at astrophysically relevant energies by measuring
the cross section for the Trojan Horse reaction in
quasi-free kinematics. We present the theory of the Trojan Horse method for
resonant binary subreactions based on the half-off-energy-shell R matrix
approach which takes into account the off-energy-shell effects and initial and
final state interactions.Comment: 6 pages and 1 figur
Astrophysical S factor for the radiative capture 12N(p,gamma)13O determined from the 14N(12N,13O)13C proton transfer reaction
The cross section of the radiative proton capture reaction on the drip line
nucleus 12N was investigated using the Asymptotic Normalization Coefficient
(ANC) method. We have used the 14N(12N,13O)13C proton transfer reaction at 12
MeV/nucleon to extract the ANC for 13O -> 12N + p and calculate from it the
direct component of the astrophysical S factor of the 12N(p,gamma)13O reaction.
The optical potentials used and the DWBA analysis of the proton transfer
reaction are discussed. For the entrance channel, the optical potential was
inferred from an elastic scattering measurement carried out at the same time
with the transfer measurement. From the transfer, we determined the square of
the ANC, C^2(13Og.s.) = 2.53 +/- 0.30 fm-1, and hence a value of 0.33(4) keVb
was obtained for the direct astrophysical S factor at zero energy. Constructive
interference at low energies between the direct and resonant captures leads to
an enhancement of Stotal(0) = 0.42(5) keVb. The 12N(p,gamma)13O reaction was
investigated in relation to the evolution of hydrogen-rich massive Population
III stars, for the role that it may play in the hot pp-chain nuclear burning
processes, possibly occurring in such objects.Comment: 15 pages, 10 figures, 3 tables submitted to Phys. Rev.
Breakup of B-8 and the S-17 astrophysical factor reexamined
Journals published by the American Physical Society can be found at http://publish.aps.org/Existing experimental data for the breakup of B-8 at energies from 30 to 1000 MeV/nucleon on light through heavy targets are analyzed in detail in terms of an extended Glauber model. The predictions of the model are in excellent agreement with independent reaction data (reaction cross sections and parallel momentum distributions for corelike fragments). Final-state interactions have been included in the Coulomb dissociation component. We extract asymptotic normalization coefficients (ANC) from which the astrophysical factor S-17(0) for the key reaction for solar neutrino production, Be-7(p,gamma)B-8, can be evaluated. Glauber model calculations using different effective interactions give consistent, though slightly different results. The differences give a measure of the precision one can expect from the method. The unweighted average of all ANCs extracted leads to S-17(0)=18.7+/-1.9 eV b. The results of this new analysis are compared with the earlier one. They are consistent with the values from most direct measurements and other indirect methods
Asymptotic Normalization Coefficients for 13C+p->14N
The proton exchange reaction has been measured
at an incident energy of 162 MeV. Angular distributions were obtained for
proton transfer to the ground and low lying excited states in . Elastic
scattering of on also was measured out to the rainbow angle
region in order to find reliable optical model potentials. Asymptotic
normalization coefficients for the system have been
found for the ground state and the excited states at 2.313, 3.948, 5.106 and
5.834 MeV in . These asymptotic normalization coefficients will be used
in a determination of the S-factor for at solar
energies from a measurement of the proton transfer reaction
.Comment: 5 pages, 6 figure
Radius of B-8 halo from the asymptotic normalization coefficient
Journals published by the American Physical Society can be found at http://publish.aps.org/The experimental asymptotic normalization coefficient determined from peripheral transfer reactions is used to obtain the root-mean-square radius of the wave function for the loosely bound proton in SB. It is shown that the asymptotic region contributes most and that matching of the interior wave function with the asymptotic part yields a nearly model-independent radius. We obtain [r(2)] (1/2) = 4.20 +/- 0.22 fm for the root-mean-square (rms) radius of the last proton, much larger than the rms radius of the Be-7 core. This large value and the fact that the asymptotic part of the proton wave function contributes 85% to the rms radius are good sign that B-8 is a halo nucleus
Asymptotic normalization coefficient of ^{8}B from breakup reactions and the S_{17} astrophysical factor
We show that asymptotic normalization coefficients (ANC) can be extracted
from one nucleon breakup reactions of loosely bound nuclei at 30-300 MeV/u. In
particular, the breakup of ^{8}B is described in terms of an extended Glauber
model. The 8B ANC extracted for the ground state of this nucleus from breakup
data at several energies and on different targets, C^2 = 0.450+/-0.039} fm^-1,
leads to the astrophysical factor S_{17}(0)= 17.4+/-1.5 eVb for the key
reaction for solar neutrino production 7Be(p,gamma)8B. The procedure described
here is more general, providing an indirect method to determine reaction rates
of astrophysical interest with beams of loosely bound radioactive nuclei.Comment: 4 pages, RevTex, 3 figures revised version to appear in Phys Rev Let
- …