Pop III GRBs: an estimative of the event rate for future surveys

We discuss the theoretical event rate of gamma-ray bursts (GRBs) from the collapse of massive primordial stars. We construct a theoretical model to calculate the rate and detectability of these GRBs taking into account all important feedback and recent results from numerical simulations of pristine gas. We expect to observe a maximum of N $\lesssim$ 0.2 GRBs per year integrated over at z > 6 with \textit{Swift} and N $\lesssim$ 10 GRBs per year integrated over at z > 6 with EXIST.Comment: 6 pages, 2 figures, published in Proceedings of the Gamma-Ray Bursts 2012 Conference (GRB 2012

AMADA-Analysis of Multidimensional Astronomical Datasets

We present AMADA, an interactive web application to analyse multidimensional datasets. The user uploads a simple ASCII file and AMADA performs a number of exploratory analysis together with contemporary visualizations diagnostics. The package performs a hierarchical clustering in the parameter space, and the user can choose among linear, monotonic or non-linear correlation analysis. AMADA provides a number of clustering visualization diagnostics such as heatmaps, dendrograms, chord diagrams, and graphs. In addition, AMADA has the option to run a standard or robust principal components analysis, displaying the results as polar bar plots. The code is written in R and the web interface was created using the Shiny framework. AMADA source-code is freely available at https://goo.gl/KeSPue, and the shiny-app at http://goo.gl/UTnU7I.Comment: Accepted for publication in Astronomy & Computin

Random Primordial Magnetic Fields and the Gas Content of Dark Matter Halos

We recently predicted the existence of random primordial magnetic fields (RPMF) in the form of randomly oriented cells with dipole-like structure with a cell size $L_0$ and an average magnetic field $B_0$. Here we investigate models for primordial magnetic field with a similar web-like structure, and other geometries, differing perhaps in $L_0$ and $B_0$. The effect of RPMF on the formation of the first galaxies is investigated. The filtering mass, $M_F$, is the halo mass below which baryon accretion is severely depressed. We show that these RPMF could influence the formation of galaxies by altering the filtering mass and the baryon gas fraction of a halo, $f_g$. The effect is particularly strong in small galaxies. We find, for example, for a comoving B_0=0.1\muG, and a reionization epoch that starts at $z_s=11$ and ends at $z_e=8$, for $L_0=100\,\text{pc}$ at $z=12$, the $f_g$ becomes severely depressed for M<10^7\msun, whereas for $B_0=0$ the $f_g$ becomes severely depressed only for much smaller masses, M<10^5\msun. We suggest that the observation of $M_F$ and $f_g$ at high redshifts can give information on the intensity and structure of primordial magnetic fields.Comment: 7 pages, 10 figures, accepted for publication in MNRAS (several improvements after suggestions of the referee

Discrete and finite Genral Relativity

We develop the General Theory of Relativity in a formalism with extended causality that describes physical interaction through discrete, transversal and localized pointlike fields. The homogeneous field equations are then solved for a finite, singularity-free, point-like field that we associate to a ``classical graviton". The standard Einstein's continuous formalism is retrieved by means of an averaging process, and its continuous solutions are determined by the chosen imposed symetry. The Schwarzschild metric is obtained by the imposition of spherical symmetry on the averaged field.Comment: Modified conform the version to appear in Classical and Quantum Gravit