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arXiv:0711.4060 [ps, pdf, other] :
Title: Comment on "Correlation of the Highest-Energy Cosmic Rays with Nearby Extragalactic Objects"
Authors: Dmitry Gorbunov, Peter Tinyakov, Igor Tkachev, Sergey Troitsky
Comments: 1000 words, 2 figures, scicite.sty
We argue that the data published by the Pierre Auger Collaboration (arXiv:0711.2256) disfavor at 99% confidence level their hypothesis that most of the highest-energy cosmic rays are protons from nearby astrophysical sources, either Active Galactic Nuclei or other objects with a similar spatial distribution. |
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arXiv:0711.4621 [ps, pdf, other] :
Title: Extracting the Gamma Ray Signal from Dark Matter Annihilation in the Galactic Center Region
Authors: Scott Dodelson, Dan Hooper, Pasquale Serpico
Comments: 8 pages, 5 figures
The GLAST satellite mission will study the gamma ray sky with considerably greater exposure than its predecessor EGRET. In addition, it will be capable of measuring the arrival directions of gamma rays with much greater precision. These features each significantly enhance GLAST's potential for identifying gamma rays produced in the annihilations of dark matter particles. The combined use of spectral and angular information, however, is essential if the full sensitivity of GLAST to dark matter is to be exploited. In this paper, we discuss techniques for separating dark matter annihilation products from astrophysical backgrounds, focusing on the Galactic Center region, and perform a forecast for such an analysis. We consider both point-like and diffuse astrophysical backgrounds and model them using a realistic point-spread-function for GLAST. While the results of our study depend on the specific characteristics of the dark matter signal and astrophysical backgrounds, we find that in many scenarios it is possible to successfully identify dark matter annihilation radiation, even in the presence of significant astrophysical backgrounds. |
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arXiv:0711.4078 [ps, pdf, other] :
Title: Quasistars: Accreting black holes inside massive envelopes
Authors: Mitchell C. Begelman, Elena M. Rossi, Philip J. Armitage
Comments: 11 pages, 9 figures, MNRAS submitted. Resubmitted version after referee review
We study the structure and evolution of "quasistars," accreting black holes embedded within massive hydrostatic gaseous envelopes. These configurations may model the early growth of supermassive black hole seeds. The accretion rate onto the black hole adjusts so that the luminosity carried by the convective envelope equals the Eddington limit for the total mass. This greatly exceeds the Eddington limit for the black hole mass alone, leading to rapid growth of the black hole. We use analytic models and numerical stellar structure calculations to study the structure and evolution of quasistars. We derive analytically the scaling of the photospheric temperature with the black hole mass and envelope mass, and show that it decreases with time as the black hole mass increases. Once the photospheric temperature becomes lower than 10000 K, the photospheric opacity drops precipitously and the photospheric temperature hits a limiting value, analogous to the Hayashi track for red giants and protostars, below which no hydrostatic solution for the convective envelope exists. For metal-free (Population III) opacities this limiting temperature is approximately 4000 K. After a quasistar reaches this limiting temperature, the envelope is rapidly dispersed by radiation pressure. We find that black hole seeds with masses between 1000 and 10000 solar masses could form via this mechanism in less than a few Myr. |
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arXiv:0711.3640 [ps, pdf, other] :
Title: Large-Scale Anisotropic Correlation Function of SDSS Luminous Red Galaxies
Authors: Teppei Okumura, Takahiko Matsubara, Daniel J. Eisenstein, Issha Kayo, Chiaki Hikage, Alexander S. Szalay, Donald P. Schneider
Comments: 10 pages, 9 figures, 1 table, submitted to ApJ
We study the large-scale anisotropic two-point correlation function using 46,760 Luminous Red Galaxies at redshifts 0.16 to 0.47 from the Sloan Digital Sky Survey. We measure the correlation function as a function of separations parallel and perpendicular to the line-of-sight in order to take account of anisotropy of the large-scale structure in redshift space. We find a slight signal of baryonic features in the anisotropic correlation function, i.e., a ``baryon ridge'' which corresponds to a baryon acoustic peak in the spherically averaged correlation function which has already been reported using the same sample. The baryon ridge has primarily a spherical structure with a known radius in comoving coordinates. It enables us to divide the redshift distortion effects into dynamical and geometrical components and provides further constraints on cosmological parameters, including the dark energy equation-of-state. With an assumption of a flat $\Lambda$ cosmology, we find the best-fit values of $\Omega_{\rm m} = 0.218^{+0.047}_{-0.037}$ and $\Omega_{\rm b} = 0.047^{+0.016}_{-0.016}$ (68% C.L.) when we use the overall shape of the anisotropic correlation function of $40<s<200\himpc$ including a scale of baryon acoustic oscillations. When an additional assumption $\Omega_{\rm b}h^2=0.024$ is adopted, we obtain $\Omega_{\rm DE}=0.770^{+0.051}_{-0.040}$ and $w=-0.93^{+0.45}_{-0.35}$. These constraints are estimated only from our data of the anisotropic correlation function, and they agree quite well with values both from the CMB anisotropies and from other complementary statistics using the LRG sample. With the CMB prior from the 3-year WMAP results, we give stronger constraints on those parameters. |
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arXiv:0711.2521 [ps, pdf, other] :
Title: Resumming Cosmological Perturbations via the Lagrangian Picture: One-loop Results in Real Space and in Redshift Space
Authors: Takahiko Matsubara
Comments: 17 pages, 11 figures
We develop a new approach to study the nonlinear evolution in the large-scale structure of the universe both in real space and in redshift space, extending the standard perturbation theory of gravitational instability. Infinite series of terms in standard Eulerian perturbation theory are resummed as a result of our starting from a Lagrangian description of perturbations. Delicate nonlinear effects on scales of the baryon acoustic oscillations are more accurately described by our method than the standard one. Our approach differs from other resummation techniques recently proposed, such as the renormalized perturbation theory, etc., in that we use simple techniques and thus resulting equations are undemanding to evaluate, and that our approach is capable of quantifying the nonlinear effects in redshift space. The power spectrum and correlation function of our approach are in good agreement with numerical simulations in literature on scales of baryon acoustic oscillations. Especially nonlinear effects on the the baryon acoustic peak of the correlation function is accurately described both in real space and in redshift space. Our approach provides a unique opportunity to analytically investigate the nonlinear effects on baryon acoustic scales in observable redshift space, which is requisite in constraining the nature of dark energy, the curvature of the universe, etc., by redshift surveys. |
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arXiv:0711.3603 [ps, pdf, other] :
Title: The Effect of Primordial Non--Gaussianity on the Topology of Large-Scale Structure
Authors: Chiaki Hikage, Peter Coles, Margherita Grossi, Lauro Moscardini, Klaus Dolag, Enzo Branchini, Sabino Matarrese
Comments: 9 pages, 3 figures, submitted to MNRAS
We study the effect of primordial non--Gaussianity on the development of large-scale cosmic structure using high-resolution N-body simulations. In particular, we focus on the topological properties of the ``cosmic web'', quantitatively characterized by the Minkowski Functionals, for models with quadratic non-linearities with different values of the usual non--Gaussianity parameter fNL. In the weakly non-linear regime, we find that analytic formulae derived from perturbation theory agree with the numerical results within a few percent of the amplitude of each MF when |fNL|<1000. In the non-linear regime, the detailed behavior of the MFs as functions of threshold density deviates more strongly from the analytical curves, while the overall amplitude of the primordial non--Gaussian effect remains comparable to the perturbative prediction. When smaller-scale information is included, the influence of primordial non--Gaussianity becomes increasingly significant statistically due to decreasing sample variance. We find that the effect of the primordial non-Gaussianity with |fNL|=50 is comparable to the sample variance of mass density fields with a volume of 0.125(Gpc/h)^3 when they are smoothed by Gaussian filter at a scale of 5Mpc/h. The detectability of this effect in actual galaxy surveys will strongly depend upon residual uncertainties in cosmological parameters and galaxy biasing. |
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arXiv:0711.4389 [ps, pdf, other] :
Title: Magnetic Field Amplification and Rapid Time Variations in SNR RX J1713.7-3946
Authors: Donald C. Ellison, Andrey Vladimirov
Comments: Submitted to ApJ Letters October 2007, 5 pages with 2 figures
Evidence is accumulating suggesting that collisionless shocks in supernova remnants (SNRs) can amplify the interstellar magnetic field to hundreds of microgauss or even milli-gauss levels, as recently claimed for SNR RX J1713.7-3946. If these fields exist, they are almost certainly created by magnetic field amplification (MFA) associated with the efficient production of cosmic rays by diffusive shock acceleration (DSA) and their existence strengthens the case for SNRs being the primary source of galactic cosmic ray ions to the `knee' and beyond. However, the high magnetic field values in SNRs are obtained exclusively from the interpretation of observations of radiation from relativistic electrons and if MFA via nonlinear DSA produces these fields the magnetic field that determines the maximum ion energy will be substantially less than the field that determines the maximum electron energy. We use results of a steady-state Monte Carlo simulation to show how nonlinear effects from efficient cosmic ray production and MFA reduce the maximum energy of protons relative to what would be expected from test-particle acceleration. |
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