Combining the Swift/BAT and the INTEGRAL/ISGRI observations

Current surveys of Active Galactic Nuclei (AGN) find only a very small fraction of AGN contributing to the Cosmic X-ray Background (CXB) at energies above 15 keV. Roughly 99% of the CXB is so far unresolved. In this work we address the question of the unresolved component of the CXB with the combined surveys of INTEGRAL and Swift. These two currently flying X-ray missions perform independent surveys at energies above 15 keV. Our approach is to perform the independent surveys and merge them in order to enhance the exposure time and reduce the systematic uncertainties. We do this with resampling techniques. As a result we obtain a new survey over a wide sky area of 6200 deg2 that is a factor ~4 more sensitive than the survey of Swift or INTEGRAL alone. Our sample comprises more than 100 AGN. We use the extragalactic source sample to resolve the CXB by more than a factor 2 compared to current parent surveys.Comment: 4 pages, 1 figure. To appear on World Scientific Vol.7 "Proceedings of the 13th ICATPP Conference on Astroparticle, Particle, Space Physics and Detectors for Physics Applications

Deeply x-raying the high-energy sky

All-sky explorations by Fermi-LAT have revolutionized our view of the gamma-ray sky. While its ongoing all-sky survey counts thousands of sources, essential issues related to the nature of unassociated sources call for sensitive all-sky surveys at hard X-ray energies that allow for their identification. We present the results of the association of the Fermi-LAT second source catalog to hard X-ray detected sources.Comment: 5 pages, 4 figures, submitted JPC

Scaling of the linear response function from zero field cooled and thermoremanent magnetization in phase ordering kinetics

In this paper we investigate the relation between the scaling properties of the linear response function $R(t,s)$, of the thermoremanent magnetization (TRM) and of the zero field cooled magnetization (ZFC) in the context of phase ordering kinetics. We explain why the retrival of the scaling properties of $R(t,s)$ from those of TRM and ZFC is not trivial. Preasymptotic contributions generate a long crossover in TRM, while ZFC is affected by a dangerous irrelevant variable. Lack of understanding of both these points has generated some confusion in the literature. The full picture relating the exponents of all the quantities involved is explicitely illustrated in the framework of the large $N$ model. Following this scheme, an assessment of the present status of numerical simulations for the Ising model can be made. We reach the conclusion that on the basis of the data available up to now, statements on the scaling properties of $R(t,s)$ can be made from ZFC but not from TRM. From ZFC data for the Ising model with $d=2,3,4$ we confirm the previously found linear dependence on dimensionality of the exponent $a$ entering $R(t,s) \sim s^{-(1+a)}f(t/s)$. We also find evidence that a recently derived form of the scaling function $f(x)$, using local scale invariance arguments [M.Henkel, M.Pleimling, C.Godr\`{e}che and J.M.Luck, Phys.Rev.Lett. {\bf 87}, 265701 (2001)], does not hold for the Ising model.Comment: 26 pages, 14 figure

Comment on "Scaling of the linear response in simple aging systems without disorder"

We have repeated the simulations of Henkel, Paessens and Pleimling (HPP) [Phys.Rev.E {\bf 69}, 056109 (2004)] for the field-cooled susceptibility $\chi_{FC}(t) - \chi_0 \sim t^{-A}$ in the quench of ferromagnetic systems to and below $T_C$. We show that, contrary to the statement made by HPP, the exponent $A$ coincides with the exponent $a$ of the linear response function $R(t,s) \sim s^{-(1+a)}f_R(t/s)$. We point out what are the assumptions in the argument of HPP that lead them to the conclusion $A<a$.Comment: 4 pages, 4 figure

Semiclassical states for weakly coupled nonlinear Schr\"odinger systems

We consider systems of weakly coupled Schr\"odinger equations with nonconstant potentials and we investigate the existence of nontrivial nonnegative solutions which concentrate around local minima of the potentials. We obtain sufficient and necessary conditions for a sequence of least energy solutions to concentrate.Comment: 23 pages, no figure

A Robust BAO Extractor

We define a procedure to extract the oscillating part of a given nonlinear Power Spectrum, and derive an equation describing its evolution including the leading effects at all scales. The intermediate scales are taken into account by standard perturbation theory, the long range (IR) displacements are included by using consistency relations, and the effect of small (UV) scales is included via effective coefficients computed in simulations. We show that the UV effects are irrelevant in the evolution of the oscillating part, while they play a crucial role in reproducing the smooth component. Our "extractor" operator can be applied to simulations and real data in order to extract the Baryonic Acoustic Oscillations (BAO) without any fitting function and nuisance parameter. We conclude that the nonlinear evolution of BAO can be accurately reproduced at all scales down to $z=0$ by our fast analytical method, without any need of extra parameters fitted from simulations.Comment: Published version, 20 pages, 8 figure

Off-equilibrium generalization of the fluctuation dissipation theorem for Ising spins and measurement of the linear response function

We derive for Ising spins an off-equilibrium generalization of the fluctuation dissipation theorem, which is formally identical to the one previously obtained for soft spins with Langevin dynamics [L.F.Cugliandolo, J.Kurchan and G.Parisi, J.Phys.I France \textbf{4}, 1641 (1994)]. The result is quite general and holds both for dynamics with conserved and non conserved order parameter. On the basis of this fluctuation dissipation relation, we construct an efficient numerical algorithm for the computation of the linear response function without imposing the perturbing field, which is alternative to those of Chatelain [J.Phys. A \textbf{36}, 10739 (2003)] and Ricci-Tersenghi [Phys.Rev.E {\bf 68}, 065104(R) (2003)]. As applications of the new algorithm, we present very accurate data for the linear response function of the Ising chain, with conserved and non conserved order parameter dynamics, finding that in both cases the structure is the same with a very simple physical interpretation. We also compute the integrated response function of the two dimensional Ising model, confirming that it obeys scaling $\chi (t,t_w)\simeq t_w^{-a}f(t/t_w)$, with $a =0.26\pm 0.01$, as previously found with a different method.Comment: 12 pages, 5 figure

Extracting the BAO scale from BOSS DR12 dataset

We present the first application to real data from the BOSS DR12 dataset of the Extractor procedure to determine the acoustic scale imprinted on Baryonic Acoustic Oscillations (BAO). We show that, being largely insensitive to the broadband shape of the Power Spectrum, this procedure requires a lower number of nuisance parameters than those used by the BOSS collaboration, For non-reconstructed data our analysis improves the accuracy on the acoustic scale by about 20 %, while for reconstructed ones we get essentially the same level of accuracy as the BOSS analysis.Comment: 16 pages, replaced to match with the published versio

Phase ordering in 3d disordered systems

We study numerically the phase-ordering kinetics of the site-diluted and bond-diluted Ising models after a quench from an infinite to a low temperature. We show that the speed of growth of the ordered domain's size is non-monotonous with respect to the amount of dilution $D$: Starting from the pure case $D=0$ the system slows down when dilution is added, as it is usually expected when disorder is introduced, but only up to a certain value $D^*$ beyond which the speed of growth raises again. We interpret this counterintuitive fact in a renormalization-group inspired framework, along the same lines proposed for the corresponding two-dimensional systems, where a similar pattern was observed.Comment: 8 pages, 4 figures.To appear on Journal of Statistical Mechanics: Theory and Experiment. arXiv admin note: text overlap with arXiv:1306.514