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

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 $a$. A similar effect occurs in a magnetic field if the magnetic length $L_m$ becomes shorter than $a(D_{||}/D_\perp)^\gamma$, where \D_{||}/D_\perp is the ratio of the diffusion coefficients parallel and perpendicular to the planes or chains. $\gamma$ depends on the direction of the magnetic field, e.g. $\gamma=1/4$ 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

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

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

In which shell-type SNRs should we look for gamma-rays and neutrinos from p-p collisions?

We present a simple analytic model for the various contributions to the non-thermal emission from shell type SNRs, and show that this model's results reproduce well the results of previous detailed calculations. We show that the \geq 1 TeV gamma ray emission from the shell type SNRs RX J1713.7-3946 and RX J0852.0-4622 is dominated by inverse-Compton scattering of CMB photons (and possibly infra-red ambient photons) by accelerated electrons. Pion decay (due to proton-proton collisions) is shown to account for only a small fraction, \lesssim10^-2, of the observed flux, as assuming a larger fractional contribution would imply nonthermal radio and X-ray synchrotron emission and thermal X-ray Bremsstrahlung emission that far exceed the observed radio and X-ray fluxes. Models where pion decay dominates the \geq 1 TeV flux avoid the implied excessive synchrotron emission (but not the implied excessive thermal X-ray Bremsstrahlung emission) by assuming an extremely low efficiency of electron acceleration, K_ep \lesssim 10^-4 (K_ep is the ratio of the number of accelerated electrons and the number of accelerated protons at a given energy). We argue that observations of SNRs in nearby galaxies imply a lower limit of K_ep \gtrsim 10^-3, and thus rule out K_ep values \lesssim 10^-4 (assuming that SNRs share a common typical value of K_ep). It is suggested that SNRs with strong thermal X-ray emission, rather than strong non-thermal X-ray emission, are more suitable candidates for searches of gamma rays and neutrinos resulting from proton-proton collisions. In particular, it is shown that the neutrino flux from the SNRs above is probably too low to be detected by current and planned neutrino observatories (Abridged).Comment: 13 pages, 1 figure, accepted for publication in JCAP, minor revision

Gate-Controlled Spin-Orbit Quantum Interference Effects in Lateral Transport

In situ control of spin-orbit coupling in coherent transport using a clean GaAs/AlGaAs 2DEG is realized, leading to a gate-tunable crossover from weak localization to antilocalization. The necessary theory of 2D magnetotransport in the presence of spin-orbit coupling beyond the diffusive approximation is developed and used to analyze experimental data. With this theory the Rashba contribution and linear and cubic Dresselhaus contributions to spin-orbit coupling are separately estimated, allowing the angular dependence of spin-orbit precession to be extracted at various gate voltages.Comment: related papers at http://marcuslab.harvard.ed

The blast wave of Tycho's supernova remnant

We use the Chandra X-ray Observatory to study the region in the Tycho supernova remnant between the blast wave and the shocked ejecta interface or contact discontinuity. This zone contains all the history of the shock-heated gas and cosmic-ray acceleration in the remnant. We present for the first time evidence for significant spatial variations of the X-ray synchrotron emission in the form of spectral steepening from a photon index of 2.6 right at the blast wave to a value of 3.0 several arcseconds behind. We interpret this result along with the profiles of radio and X-ray intensity using a self-similar hydrodynamical model including cosmic ray backreaction that accounts for the observed ratio of radii between the blast wave and contact discontinuity. Two different assumptions were made about the post-shock magnetic field evolution: one where the magnetic field (amplified at the shock) is simply carried by the plasma flow and remains relatively high in the post-shock region [synchrotron losses limited rim case], and another where the amplified magnetic field is rapidly damped behind the blast wave [magnetic damping case]. Both cases fairly well describe the X-ray data, however both fail to explain the observed radio profile. The projected synchrotron emission leaves little room for the presence of thermal emission from the shocked ambient medium. This can only be explained if the pre-shock ambient medium density in the vicinity of the Tycho supernova remnant is below 0.6 cm-3.Comment: Accepted for publication in ApJ - 61 pages, 17 figure

Molecular and atomic gas in the young TeV \gamma-ray SNRs RX J1713.7-3946 and RX J0852.0-4622; evidence for the hadronic production of \gamma-rays

The interstellar molecular clouds are the site of star formation and also the target for the cosmic ray protons to produce \gamma-rays via the hadronic process. The interstellar atomic gas is enveloping the molecular clouds and may also be dense enough to affect the \gamma-ray production. In this Chapter, some of the basic properties of the interstellar gas both in molecular and atomic forms will be reviewed. Then, it is presented that two young TeV \gamma-ray SNRs, RX J1713.7-3946 and RX J0852.0-4622, show good spatial correspondence between the \gamma-rays and the interstellar protons. The good spatial correspondence provides a support for the hadronic origin of the \gamma-rays in these SNRs. It is emphasized that both molecular and atomic hydrogen plays a role as targets for cosmic ray (CR) protons. The clumpy distribution of the target interstellar medium (ISM) protons is crucial in the interaction of the supernova shocks with the ISM, whereas models with uniform ISM distribution are not viable. Finally, it is suggested that the dense atomic gas without molecules may occupy the dominant part of the dark gas in the local ISM.Comment: 23 pages, 15 figures, To appear in "Cosmic Rays in Star-Forming Environments: Proceedings of the Second Session of the Sant Cugat Forum on Astrophysics" (April 16-19, 2012), Torres, Diego F. and Reimer, Olaf (Eds.

The Potential Energy Surface in Molecular Quantum Mechanics

The idea of a Potential Energy Surface (PES) forms the basis of almost all accounts of the mechanisms of chemical reactions, and much of theoretical molecular spectroscopy. It is assumed that, in principle, the PES can be calculated by means of clamped-nuclei electronic structure calculations based upon the Schr\"{o}dinger Coulomb Hamiltonian. This article is devoted to a discussion of the origin of the idea, its development in the context of the Old Quantum Theory, and its present status in the quantum mechanics of molecules. It is argued that its present status must be regarded as uncertain.Comment: 18 pages, Proceedings of QSCP-XVII, Turku, Finland 201