A systematic analysis of X-ray afterglows of gamma-ray burst observed by XMM-Newton

This work is part of a systematic re-analysis program of all the data of Gamma-Ray Burst (GRB) X-ray afterglows observed so far, in order to constrain the GRB models. We present here a systematic analysis of those afterglows observed by XMM-Newton between January 2000 and March 2004. This dataset includes GRB 011211 and GRB 030329. We have obtained spectra, light curves and colors for these afterglows. In this paper we focus on the continuum spectral and temporal behavior. We compare these values with the theoretical ones expected from the fireball model. We derive constraints about the burst environment (absorption, density profile) and put constraints on their beaming angle.Comment: 7 pages, 2 figures, COSPAR proceeding accepted for publication in Advances in Space Researc

Nonlinear Relaxation in Population Dynamics

We analyze the nonlinear relaxation of a complex ecosystem composed of many interacting species. The ecological system is described by generalized Lotka-Volterra equations with a multiplicative noise. The transient dynamics is studied in the framework of the mean field theory and with random interaction between the species. We focus on the statistical properties of the asymptotic behaviour of the time integral of the i-th population and on the distribution of the population and of the local field.Comment: 11 pages, 4 figures, in press in Int. Journal of Fractals (2001

A Correlation Between the Intrinsic Brightness and Average Decay Rate of Gamma-ray Burst X-ray Afterglow Light Curves

We present a correlation between the average temporal decay ({\alpha}X,avg,>200s) and early-time luminosity (LX,200s) of X-ray afterglows of gamma-ray bursts as observed by Swift-XRT. Both quantities are measured relative to a rest frame time of 200 s after the {\gamma}-ray trigger. The luminosity average decay correlation does not depend on specific temporal behavior and contains one scale independent quantity minimizing the role of selection effects. This is a complementary correlation to that discovered by Oates et al. (2012) in the optical light curves observed by Swift-UVOT. The correlation indicates that on average, more luminous X-ray afterglows decay faster than less luminous ones, indicating some relative mechanism for energy dissipation. The X-ray and optical correlations are entirely consistent once corrections are applied and contamination is removed. We explore the possible biases introduced by different light curve morphologies and observational selection effects, and how either geometrical effects or intrinsic properties of the central engine and jet could explain the observed correlation.Comment: Accepted for Publication in ApJ; 16 pages, 15 figures, 2 table

Soil-Transmitted Helminths in Schoolchildren in Grand Bois Haiti: A Prevalence Study

This study used secondary data collected in 2006 to assess the prevalence and severity of three common soil-transmitted helminths in schoolchildren in rural, mountainous, eastern Haiti, and using a case-control design looked at age and gender as independent risk factors, and at anemia and growth failure as potential outcomes of infection. The primary aim was to determine if prevalence and severity were high enough to meet World Health Organization (WHO) population-based deworming criteria. Results do support mass deworming, but overall, indicate no correlation between the other independent variables or outcome measures with presence of disease. A secondary data set from the coastal town of Leogane, Haiti was used as a comparison population where a similar study was performed in 1996. Based on findings, recommendations will be made to Haitian health authorities

An Estimation of the Gamma-Ray Burst Afterglow Apparent Optical Brightness Distribution Function

By using recent publicly available observational data obtained in conjunction with the NASA Swift gamma-ray burst mission and a novel data analysis technique, we have been able to make some rough estimates of the GRB afterglow apparent optical brightness distribution function. The results suggest that 71% of all burst afterglows have optical magnitudes with mR < 22.1 at 1000 seconds after the burst onset, the dimmest detected object in the data sample. There is a strong indication that the apparent optical magnitude distribution function peaks at mR ~ 19.5. Such estimates may prove useful in guiding future plans to improve GRB counterpart observation programs. The employed numerical techniques might find application in a variety of other data analysis problems in which the intrinsic distributions must be inferred from a heterogeneous sample.Comment: 15 pages including 2 tables and 7 figures, accepted for publication in Ap

GRB Flares: UV/Optical Flaring (Paper I)

We present a new algorithm for the detection of flares in gamma-ray burst (GRB) light curves and use this algorithm to detect flares in the UV/optical. The algorithm makes use of the Bayesian Information Criterion (BIC) to analyze the residuals of the fitted light curve, removing all major features, and to determine the statistically best fit to the data by iteratively adding additional `breaks' to the light curve. These additional breaks represent the individual components of the detected flares: T_start, T_stop, and T_peak. We present the detection of 119 unique flaring periods detected by applying this algorithm to light curves taken from the Second Swift Ultraviolet/Optical Telescope (UVOT) GRB Afterglow Catalog. We analyzed 201 UVOT GRB light curves and found episodes of flaring in 68 of the light curves. For those light curves with flares, we find an average number of ~2 flares per GRB. Flaring is generally restricted to the first 1000 seconds of the afterglow, but can be observed and detected beyond 10^5 seconds. More than 80% of the flares detected are short in duration with Delta t/t of < 0.5. Flares were observed with flux ratios relative to the underlying light curve of between 0.04 to 55.42. Many of the strongest flares were also seen at greater than 1000 seconds after the burst.Comment: Submitted to ApJ. 20 pages (including 8 figures and 1 table

Generation of short and long range temporal correlated noises

We present the implementation of an algorithm to generate Gaussian random noises with prescribed time correlations that can be either long or short ranged. Examples of Langevin dynamics with short and long range noises are presented and discussed.Comment: 7 pages, 6 figs, submitted to J. Comp. Phy