Entity

Time filter

Source Type


Jones D.I.,Max Planck Institute for Nuclear Physics | Burton M.,Radboud University Nijmegen | Jones P.,Radboud University Nijmegen | Rowell G.,University of New South Wales | And 3 more authors.
AIP Conference Proceedings | Year: 2012

We explore the correlation of diffuse TeV gamma rays in the Galactic centre with optical-depth-corrected CO(1-0) emission. We present our analysis of the data, in which the 12CO(1-0) molecular line emission is corrected for optical-depth by using the the 13C and 18O isotopes of the CO(1-0) line. Using simple scatter plots, we find no evidence of a correlation with the lower-density tracer. © 2012 American Institute of Physics. Source


Becker T.W.,University of Southern California | Lebedev S.,Dublin Institute for Advanced Study | Long M.D.,Yale University
Journal of Geophysical Research: Solid Earth | Year: 2012

Seismic anisotropy provides essential constraints on mantle dynamics and continental evolution. One particular question concerns the depth distribution and coherence of azimuthal anisotropy, which is key for understanding force transmission between the lithosphere and asthenosphere. Here, we reevaluate the degree of coherence between the predicted shear wave splitting derived from tomographic models of azimuthal anisotropy and that from actual observations of splitting. Significant differences between the two types of models have been reported, and such discrepancies may be due to differences in averaging properties or due to approximations used in previous comparisons. We find that elaborate, full waveform methods to estimate splitting from tomography yield generally similar results to the more common, simplified approaches. This validates previous comparisons and structural inversions. However, full waveform methods may be required for regional studies, and they allow exploiting the back-azimuthal variations in splitting that are expected for depth-variable anisotropy. Applying our analysis to a global set of SKS splitting measurements and two recent surface wave models of upper-mantle azimuthal anisotropy, we show that the measures of anisotropy inferred from the two types of data are in substantial agreement. Provided that the splitting data is spatially averaged (so as to bring it to the scale of long-wavelength tomographic models and reduce spatial aliasing), observed and tomography-predicted delay times are significantly correlated, and global angular misfits between predicted and actual splits are relatively low. Regional anisotropy complexity notwithstanding, our findings imply that splitting and tomography yield a consistent signal that can be used for geodynamic interpretation. Copyright 2012 by the American Geophysical Union. Source


Chishtie F.A.,University of Western Ontario | Hanif T.,University of Western Ontario | Hanif T.,University of Dhaka | Jia J.,University of Western Ontario | And 4 more authors.
International Journal of Modern Physics A | Year: 2010

When one uses the ColemanWeinberg renormalization condition, the effective potential V in the massless φ4 4 theory with O(N) symmetry is completely determined by the renormalization group functions. It has been shown how the (p + 1) order renormalization group function determine the sum of all the NpLL order contribution to V to all orders in the loop expansion. We discuss here how, in addition to fixing the NpLL contribution to V, the (p + 1) order renormalization group functions can also be used to determine portions of the Np+nLL contributions to V. When these contributions are summed to all orders, the singularity structure of V is altered. An alternate rearrangement of the contributions to V in powers of ln φ, when the extremum condition V′(φ = v) = 0 is combined with the renormalization group equation, show that either v = 0 or V is independent of φ. This conclusion is supported by showing the LL, ..., N4LL contributions to V become progressively less dependent on φ. © 2010 World Scientific Publishing Company. Source


Jones D.I.,Max Planck Institute for Nuclear Physics | Crocker R.M.,Max Planck Institute for Nuclear Physics | Reich W.,Max Planck Institute for Radio Astronomy | Ott J.,U.S. National Radio Astronomy Observatory | And 2 more authors.
Astrophysical Journal Letters | Year: 2012

We report a correspondence between giant, polarized microwave structures emerging north from the Galactic plane near the Galactic center and a number of GeV gamma-ray features, including the eastern edge of the recently discovered northern Fermi Bubble. The polarized microwave features also correspond to structures seen in the all-sky 408MHz total intensity data, including the Galactic center Spur. The magnetic field structure revealed by the Wilkinson Microwave Anisotropy Probe polarization data at 23GHz suggests that neither the emission coincident with the Bubble edge nor the Galactic center Spur are likely to be features of the local interstellar medium. On the basis of the observed morphological correspondences, similar inferred spectra, and the similar energetics of all sources, we suggest a direct connection between the Galactic center Spur and the northern Fermi Bubble. © 2012 The American Astronomical Society. All rights reserved. Source


Chernyakova M.,Dublin Institute for Advanced Study | Malyshev D.,Dublin Institute for Advanced Study | Aharonian F.A.,Dublin Institute for Advanced Study | Aharonian F.A.,Max Planck Institute for Nuclear Physics | And 2 more authors.
Astrophysical Journal | Year: 2011

Employing data collected during the first 25 months of observations by the Fermi-LAT, we describe and subsequently seek to model the very high energy (<300 MeV) emission from the central few parsecs of our Galaxy. We analyze the morphological, spectral, and temporal characteristics of the central source, 1FGL J1745.6-2900. The data show a clear, statistically significant signal at energies above 10 GeV, where the Fermi-LAT has angular resolution comparable to that of HESS at TeV energies. This makes a meaningful joint analysis of the data possible. Our analysis of the Fermi data (alone) does not uncover any statistically significant variability of 1FGL J1745.6-2900 at GeV energies on the month timescale. Using the combination of Fe r m i data on 1FGL J1745.6-2900 and HESS data on the coincident, TeV source HESS J1745-290, we show that the spectrum of the central gamma-ray source is inflected with a relatively steep spectral region matching between the flatter spectrum found at both low and high energies. We model the gamma-ray production in the inner 10 pc of the Galaxy and examine cosmic ray (CR) proton propagation scenarios that reproduce the observed spectrum of the central source. We show that a model that instantiates a transition from diffusive propagation of the CR protons at low energy to almost rectilinear propagation at high energies can explain well the spectral phenomenology. We find considerable degeneracy between different parameter choices which will only be broken with the addition of morphological information that gamma-ray telescopes cannot deliver given current angular resolution limits. We argue that a future analysis performed in combination with higher-resolution radio continuum data holds out the promise of breaking this degeneracy. © 2011. The American Astronomical Society. Source

Discover hidden collaborations