26,624 research outputs found
Clear detection of dusty torus signatures in a Weak-Line Radio Galaxy: the case of PKS 0043-42
We report the clearest detection to date of dusty torus signatures in a
Weak-Line Radio Galaxy (WLRG). The deep Spitzer InfraRed Spectrograph (IRS)
rest-frame mid-infrared (MIR) spectrum of the WLRG PKS 0043-42 (z=0.116) shows
a clear spectral turnover at wavelengths longer than ~20 micron suggestive of
warm dust, as well as a 9.7 micron silicate absorption feature. In addition,
the hard X-ray results, based on Chandra data, strongly support a picture in
which PKS 0043-42 has a torus and accretion disc more typical of Strong-Line
Radio Galaxies (SLRGs). The MIR and X-ray spectra are markedly different from
those of other WLRGs at similar redshifts, and here we show that the former can
be successfully fitted with clumpy torus models with parameters characteristic
of Type-2 AGN tori: close to edge-on (i=74 deg) and relatively broad (torus
angular width=60 deg), with an outer radius of 2 pc, hydrogen column density
~1.6x10^(23) cm^(-2), and AGN bolometric luminosity ~1.6x10^(44) erg s^(-1).
The presence of a compact torus in PKS 0043-42 provides evidence that this WLRG
is fuelled by cold, rather than hot, gas accretion. We suggest that WLRGs are a
diverse population, and PKS 0043-42 may represent a type of radio galaxy in
which the AGN activity has been recently re-triggered as a consequence of
intermittent gas supply, or in which the covering factor of the Narrow-Line
Region (NLR) clouds is relatively low.Comment: 7 pages, 6 figures, 1 table. Accepted by MNRA
Shape evolution and shape coexistence in Pt isotopes: comparing interacting boson model configuration mixing and Gogny mean-field energy surfaces
The evolution of the total energy surface and the nuclear shape in the
isotopic chain Pt are studied in the framework of the interacting
boson model, including configuration mixing. The results are compared with a
self-consistent Hartree-Fock-Bogoliubov calculation using the Gogny-D1S
interaction and a good agreement between both approaches shows up. The
evolution of the deformation parameters points towards the presence of two
different coexisting configurations in the region 176 A 186.Comment: Submitted to PR
K- absorption in nuclei by two and three nucleons
It will be shown that the peaks in the (Lambda p) and (Lambda d) invariant
mass distributions, observed in recent FINUDA experiments and claimed to be
signals of deeply bound kaonic states, are naturally explained in terms of K-
absorption by two or three nucleons leaving the rest of the original nuclei as
spectator. For reactions on heavy nuclei, the subsequent interactions of the
particles produced in the primary absorption process with the residual nucleus
play an important role. Our analyses leads to the conclusion that at present
there is no experimental evidence of deeply bound K- state in nuclei. Although
the FINUDA experiments have been done for reasons which are not supported a
posteriori, some new physics can be extracted from the data.Comment: 6 pages, 5 figures. Talk presented at the International Conference on
Exotic Atoms "EXA 2008", Vienna, Austria, September 15-18, 200
Nonequilibrium Precursor Model for the Onset of Percolation in a Two-Phase System
Using a Boltzmann equation, we investigate the nonequilibrium dynamics of
nonperturbative fluctuations within the context of Ginzburg-Landau models. As
an illustration, we examine how a two-phase system initially prepared in a
homogeneous, low-temperature phase becomes populated by precursors of the
opposite phase as the temperature is increased. We compute the critical value
of the order parameter for the onset of percolation, which signals the
breakdown of the conventional dilute gas approximation.Comment: 4 pages, 4 eps figures (uses epsf), Revtex. Replaced with version in
press Physical Review
Latest results for the antikaon-nucleon optical potential
The key question of this letter is whether the K-nucleus optical potential is
deep, as it is prefered by the phenomenological fits to kaonic atoms data, or
shallow, as it comes out from unitary chiral model calculations. The current
experimental situation is reviewed.Comment: 3 pages, 1 figure. Presented at the 21st European Conference on the
Few-Body problems in Physics (EFB21), Salamanca, Spain, August 29 - September
3, 201
Projection effects in galaxy cluster samples: insights from X-ray redshifts
Up to now, the largest sample of galaxy clusters selected in X-rays comes
from the ROSAT All-Sky Survey (RASS). Although there have been many interesting
clusters discovered with the RASS data, the broad point spread function (PSF)
of the ROSAT satellite limits the amount of spatial information of the detected
objects. This leads to the discovery of new cluster features when a
re-observation is performed with higher resolution X-ray satellites. Here we
present the results from XMM-Newton observations of three clusters:
RXCJ2306.6-1319, ZwCl1665 and RXCJ0034.6-0208, for which the observations
reveal a double or triple system of extended components. These clusters belong
to the extremely expanded HIghest X-ray FLUx Galaxy Cluster Sample
(eeHIFLUGCS), which is a flux-limited cluster sample ( erg s cm in the keV energy band). For
each structure in each cluster, we determine the redshift with the X-ray
spectrum and find that the components are not part of the same cluster. This is
confirmed by an optical spectroscopic analysis of the galaxy members.
Therefore, the total number of clusters is actually 7 and not 3. We derive
global cluster properties of each extended component. We compare the measured
properties to lower-redshift group samples, and find a good agreement. Our flux
measurements reveal that only one component of the ZwCl1665 cluster has a flux
above the eeHIFLUGCS limit, while the other clusters will no longer be part of
the sample. These examples demonstrate that cluster-cluster projections can
bias X-ray cluster catalogues and that with high-resolution X-ray follow-up
this bias can be corrected
Spectral microscopic mechanisms and quantum phase transitions in a 1D correlated problem
In this paper we study the dominant microscopic processes that generate
nearly the whole one-electron removal and addition spectral weight of the
one-dimensional Hubbard model for all values of the on-site repulsion . We
find that for the doped Mott-Hubbard insulator there is a competition between
the microscopic processes that generate the one-electron upper-Hubbard band
spectral-weight distributions of the Mott-Hubbard insulating phase and
finite-doping-concentration metallic phase, respectively. The spectral-weight
distributions generated by the non-perturbative processes studied here are
shown elsewhere to agree quantitatively for the whole momentum and energy
bandwidth with the peak dispersions observed by angle-resolved photoelectron
spectroscopy in quasi-one-dimensional compounds.Comment: 18 pages, 2 figure
Reduced sensitivity of the cross sections to the deuteron model beyond adiabatic approximation
It has recently been reported [Phys. Rev. Lett. 117, 162502 (2016)] that (d,
p) cross sections can be very sensitive to the n-p interactions used in the
adiabatic treatment of deuteron breakup with nonlocal nucleon-target optical
potentials. To understand to what extent this sensitivity could originate in
the inaccuracy of the adiabatic approximation we have developed a leading-order
local- equivalent continuum-discretized coupled-channel model that accounts for
non-adiabatic effects in the presence of nonlocality of nucleon optical
potentials. We have applied our model to the astro- physically relevant
reaction AlAl using two different n-p potentials
associated with the lowest and the highest n-p kinetic energy in the
short-range region of their interaction, respectively. Our calculations reveal
a significant reduction of the sensitivity to the high n-p momenta thus
confirming that it is mostly associated with theoretical uncertainties of the
adiabatic approximation itself. The non-adiabatic effects in the presence of
nonlocality were found to be stronger than those in the case of the local
optical potentials. These results argue for extending the analysis of the reactions, measured for spectroscopic studies, beyond the adiabatic
approximation.Comment: 6 pages, 3 figure
Perey-effect in Continuum-Discretized Coupled-Channel description of reactions
The Perey-effect in two-body channels of reactions has been known for
a long time. It arises when the nonlocal two-body deuteron-target and/or
proton-target problem is approximated by a local one, manifesting itself in a
reduction of the scattering channel wave functions in the nuclear interior.
However, the reaction mechanism requires explicit accounting for
three-body dynamics involving the target and the neutron and proton in the
deuteron. Treating nonlocality of the nucleon-target interactions within a
three-body context requires significant effort and demands going beyond the
widely-used adiabatic approximation, which can be done using a
continuum-discretized coupled-channel (CDCC) method. However, the inclusion of
nonlocal interactions into the CDCC description of reactions has not
been developed yet. Here, we point out that, similarly to the two-body nonlocal
case, nonlocality in a three-body channel can be accounted for by introducing
the Perey factors. We explain this procedure and present the first CDCC
calculations to our knowledge including the Perey-effect.Comment: 13 pages, 2 figure
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