64 research outputs found
Arguments against a dominantly hadronic origin of the VHE radiation from the supernova remnant RX J1713-3946
The flux of photons with energies above 1 TeV from the direction of the
centre and a cloud in the western part of the nearby southern supernova remnant
(SNR) RX J1713.7-3946 is calculated in the ``hadronic scenario'' that aims to
explain the intense VHE radiation from this remnant with the decay of \pi_0
pions produced in nuclear collisions. The expected flux from its centre is
found to fall short by about factor 40 from the one observed by the HESS
collaboration. This discrepancy presents a serious obstacle to the ``hadronic
scenario''. The theoretically expected flux from the molecular cloud exceeds
the one observed by HESS by at least a factor 3. While the size of this
discrepancy might still seem acceptable in the face of various theoretical
uncertainties, the result strongly suggests a strict spatial correlation of the
cloud with an excess of TeV \gamma radiation. The observational lack of such
correlations in the remnant reported by HESS is another counter argument
against the hadronic scenario. In combination these arguments cannot be refuted
by choosing certain parameters for the total energy or acceleration efficiency
of the SNR.Comment: 8 pages, small clarification and one footnote added to the published
versio
XMM-Newton observation of SNR RX J1713.7-3946
We present the first results of the observations of the supernova remnant RX
J1713.7-3946 (also G347.3-0.5) obtained with the EPIC instrument on board the
XMM-Newton satellite. We show a 5 pointings mosaiced image of the X-ray
synchrotron emission. We characterize this emission by mapping its spectral
parameters (absorbing column density NH and photon index). The synchrotron
spectrum is flat at the shock and steep in the interior of the remnant. NH is
well correlated with the X-ray brightness. A strong NH is found in the
southwest rim of RX J1713.7-3946. We suggest that the SNR is interacting with a
HI region there.Comment: 4 pages, 4 figures, To appear in "Young Neutron Stars and Their
Environments" (IAU Symposium 218, ASP Conference Proceedings), eds F. Camilo
and B. M. Gaensle
Morphological evidence for azimuthal variations of the cosmic ray ion acceleration at the blast wave of SN 1006
Using radio, X-ray and optical observations, we present evidence for
morphological changes due to efficient cosmic ray ion acceleration in the
structure of the southeastern region of the supernova remnant SN 1006. SN 1006
has an apparent bipolar morphology in both the radio and high-energy X-ray
synchrotron emission. In the optical, the shock front is clearly traced by a
filament of Balmer emission in the southeast. This optical emission enables us
to trace the location of the blast wave (BW) even in places where the
synchrotron emission from relativistic electrons is either absent or too weak
to detect. The contact discontinuity (CD) is traced using images in the
low-energy X-rays (oxygen band) which we argue reveals the distribution of
shocked ejecta. We interpret the azimuthal variations of the ratio of radii
between the BW and CD plus the X-ray and radio synchrotron emission at the BW
using CR-modified hydrodynamic models. We assumed different azimuthal profiles
for the injection rate of particles into the acceleration process, magnetic
field and level of turbulence. We found that the observations are consistent
with a model in which these parameters are all azimuthally varying, being
largest in the brightest regions.Comment: Accepted for publication in ApJ - 42 pages, 11 figure
Gamma Rays from the Tycho Supernova Remnant: Leptonic or Hadronic?
Recent Fermi and VERITAS observations of the prototypical Type Ia supernova
remnant (SNR) Tycho have discovered gamma-rays with energies E in the range
from ~0.4 GeV to 10 TeV. Crucial for the theory of Galactic cosmic-ray origin
is whether the gamma-rays from SNRs are produced by accelerated hadrons
(protons and ions), or by relativistic electrons. Here we show that the
broadband radiation spectrum of Tycho can be explained within the framework of
a two-zone leptonic model, which is likely to apply to every SNR. A model with
hadrons can also fit the radiation spectrum. The hadronic origin of gamma-rays
can be confirmed by Fermi spectral measurements of Tycho and other SNRs at
energies below ~300 MeV.Comment: 5 pages, 2 figure
Dimensional Crossover of Weak Localization in a Magnetic Field
We study the dimensional crossover of weak localization in strongly
anisotropic systems. This crossover from three-dimensional behavior to an
effective lower dimensional system is triggered by increasing temperature if
the phase coherence length gets shorter than the lattice spacing . A similar
effect occurs in a magnetic field if the magnetic length becomes shorter
than , where \D_{||}/D_\perp is the ratio of the
diffusion coefficients parallel and perpendicular to the planes or chains.
depends on the direction of the magnetic field, e.g. or
1/2 for a magnetic field parallel or perpendicular to the planes in a quasi
two-dimensional system. We show that even in the limit of large magnetic field,
weak localization is not fully suppressed in a lattice system. Experimental
implications are discussed in detail.Comment: RevTeX, 11 pages, 4 figures; three references added and discusse
A joint spectro-imaging analysis of the XMM-Newton and HESS observations of the supernova remnant RX J1713.7-3946
Context. The supernova remnant (SNR) RX J1713.7-3946 (also known as G347.3-0.5) is part of the class of remnants dominated by synchrotron emission in X-rays. It is also one of the few shell-type SNRs observed at TeV energies allowing to investigate particle acceleration at SNRs shock. Aims. Our goal is to compare spatial and spectral properties of the remnant in X- and -rays to understand the nature of the TeV emission. This requires to study the remnant at the same spatial scale at both energies. To complement the non-thermal spectrum of the remnant, we attempt to provide a reliable estimate for the radio flux density. Methods. In radio, we revisited ATCA data and used HI and mid-infrared observations to disentangle the thermal from the nonthermal emission. In X-rays, we produced a new mosaic of the remnant and degraded the spatial resolution of the X-ray data to the resolution of the HESS instrument to perform spatially resolved spectroscopy at the same spatial scale in X- and gamma-rays. Radial profiles were obtained to investigate the extension of the emission at both energies. Results. We found that part of the radio emission within the SNR contours is thermal in nature. Taking this into account, we provide new lower and upper limits for the integrated synchrotron flux of the remnant at 1.4 GHz of 22 Jy and 26 Jy respectively. In X-rays, we obtained the first full coverage of RX J1713.7-3946 with XMM-Newton. The spatial variation of the photon index seen at small scale in X-rays is smeared out at HESS resolution. A non-linear correlation between the X- and gamma-ray fluxes of the type F_X propto F_gamma^2.41 is found. If the flux variation are mainly due to density variation around the remnant then a leptonic model can more easily reproduce the observed X/ -ray correlation. In some angular sectors, radial profiles indicate that the bulk of the X-ray emission comes more from the inside of the remnant than in gamma-rays.Fil: Acero Barriga, Fabio Nelson. Université Paris Diderot - Paris 7; FranciaFil: Ballet, J.. Université Paris Diderot - Paris 7; FranciaFil: Decourchelle, A.. Université Paris Diderot - Paris 7; FranciaFil: Lemoine Goumard, M.. Centre d’Etudes nucleaires de Bordeaux Gradignan; FranciaFil: Ortega, Martin Eduardo. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Giacani, Elsa Beatriz. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Dubner, Gloria Mabel. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Cassam Chenai, G.. Osservatorio Astrofisico di Arcetri; Itali
Nonbackscattering Contribution to the Weak Localization
We show that the enhancement of backscattering responsible for the weak
localization is accompanied by reduction of the scattering in other directions.
A simple quasiclassical interpretation of this phenomenon is presented in terms
of a small change in the effective differential cross-section for a single
impurity. The reduction of the scattering at the arbitrary angles leads to the
decrease of the quantum correction to the conductivity. Within the diffusion
approximation this decrease is small, but it should be taken into account in
the case of a relatively strong magnetic field when the diffusion approximation
is not valid.Comment: 18 pages, 6 figures, Submitted to PR
Weak Field Magnetoresistance in Quasi-One-Dimensional Systems
Theoretical studies are presented on weak localization effects and
magnetoresistance in quasi-one-dimensional systems with open Fermi surfaces.
Based on the Wigner representation, the magnetoresistance in the region of weak
field has been studied for five possible configurations of current and field
with respect to the one-dimensional axis. It has been indicated that the
anisotropy and its temperature dependences of the magnetoresistance will give
information on the degree of one-dimensionality and the phase relaxation time.Comment: pages 11, LaTeX, 5 figures, uses jpsj.sty. To be published in J.
Phys. Soc. Jpn. (Vol.67(1998) No.4); Added some references and a Note at Feb.
13 199
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