126 research outputs found
LOFAR detectability of prompt low-frequency radio emission during gamma-ray burst X-ray flares
Testing the blast wave model with Swift GRBs
The complex structure of the light curves of Swift GRBs has made the
identification of breaks, and the interpretation of the blast wave caused by
the burst, more difficult than in the pre-Swift era. We aim to identify breaks,
which are possibly hidden, and to constrain the blast wave parameters; electron
energy distribution, p, density profile of the circumburst medium, k, and the
continued energy injection index, q. We do so by comparing the observed
multi-wavelength light curves and X-ray spectra of our sample to the
predictions of the blast wave model.
We can successfully interpret all of the bursts in our sample of 10, except
two, within this framework and we can estimate, with confidence, the electron
energy distribution index for 6 of the sample. Furthermore we identify jet
breaks in a number of the bursts. A statistical analysis of the distribution of
p reveals that, even in the most conservative case of least scatter, the values
are not consistent with a single, universal value. The values of k suggest that
the circumburst density profiles are not drawn from only one of the constant
density or wind-like media populations.Comment: 14 pages, accepted by MNRAS after minor changes, including extension
of discussion (section 4.3
Observational constraints on the optical and near-infrared emission from the neutron star-black hole binary merger candidate S190814bv
Spectroscopy and multiband photometry of the afterglow of intermediate duration gamma-ray burst GRB 040924 and its host galaxy
Detailed multiwavelength modelling of the dark GRB 140713A and its host galaxy
We investigate the afterglow of GRB 140713A, a gamma-ray burst (GRB) that was detected and relatively well sampled at X-ray and radio wavelengths, but was not present at optical and near-infrared wavelengths, despite searches to deep limits. We present the emission spectrum of the likely host galaxy at z = 0.935 ruling out a high-redshift explanation for the absence of the optical flux detection. Modelling the GRB multiwavelength afterglow using the radiative transfer hydrodynamics code boxfit provides constraints on physical parameters of the GRB jet and its environment, for instance a relatively wide jet opening angle and an electron energy distribution slope p below 2. Most importantly, the model predicts an optical flux about two orders of magnitude above the observed limits. We calculated that the required host extinction to explain the observed limits in the r, i, and z bands was A rm host-V gt 3.2 mag, equivalent to E(B ' V) host > 1.0 mag. From the X-ray absorption we derive that the GRB host extinction is A rm host-V = 11.6 +7.5-5.3 mag, equivalent to E(B-V) rm host = 3.7 +2.4-1.7 mag, which is consistent with the extinction required from our boxfit derived fluxes. We conclude that the origin of the optical darkness is a high level of extinction in the line of sight to the GRB, most likely within the GRB host galaxy
Opportunities for evaluating chemical exposures and child health in the United States: the Environmental influences on Child Health Outcomes (ECHO) Program
The Environmental Influences on Child Health Outcomes (ECHO) Program will evaluate environmental factors affecting children’s health (perinatal, neurodevelopmental, obesity, respiratory, and positive health outcomes) by pooling cohorts composed of >50,000 children in the largest US study of its kind. Our objective was to identify opportunities for studying chemicals and child health using existing or future ECHO chemical exposure data. We described chemical-related information collected by ECHO cohorts and reviewed ECHO-relevant literature on exposure routes, sources, and environmental and human monitoring. Fifty-six ECHO cohorts have existing or planned chemical biomonitoring data for mothers or children. Environmental phenols/parabens, phthalates, metals/metalloids, and tobacco biomarkers are each being measured by ≥15 cohorts, predominantly during pregnancy and childhood, indicating ample opportunities to study child health outcomes. Cohorts are collecting questionnaire data on multiple exposure sources and conducting environmental monitoring including air, dust, and water sample collection that could be used for exposure assessment studies. To supplement existing chemical data, we recommend biomonitoring of emerging chemicals, nontargeted analysis to identify novel chemicals, and expanded measurement of chemicals in alternative biological matrices and dust samples. ECHO’s rich data and samples represent an unprecedented opportunity to accelerate environmental chemical research to improve the health of US children
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