8,189 research outputs found
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
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
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
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
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