Optical/Multiwavelength Observations of GRB Afterglows

I review gamma-ray burst optical/multiwavelength afterglow observations since 1997, when the first counterparts to GRBs were discovered. I discuss what we have learned from multiwavelength observations of GRB afterglows in relation to the `standard' fireball plus relativistic blast-wave models. To first order the `standard' model describes the afterglow observations well, but a wealth of information can be gathered from the deviations of GRB afterglow observations from this `standard' model. These deviations provide information on the nature of the progenitor and on the physics of GRB production. In particular I focus on the possible connection of GRBs to supernovae, on jet and circumstellar wind models, on the early-time afterglow, and on the emission from the reverse shock.Comment: 10 pages, 4 figures; invited review for the 5th Huntsville Gamma-Ray Burst Workshop, eds. M. Kippen, R. Mallozzi, and G. Fishma

Discovery of a tight correlation between pulse lag/luminosity and jet-break times: a connection between gamma-ray burst and afterglow properties

A correlation is presented between the pulse lag and the jet-break time for seven BATSE gamma-ray bursts with known redshifts. This is, to our best knowledge, the first known direct tight correlation between a property of the gamma-ray burst phase (the pulse lag) and the afterglow phase (the jet-break time). As pulse lag and luminosity have been found to be correlated this also represents a correlation between peak luminosity and jet-break time. Observed timescales (variability or spectral lags) as well as peak luminosity naturally have a strong dependence on the Lorentz factor of the outflow and so we propose that much of the variety among GRBs has a purely kinematic origin (the speed or direction of the outflow). We explore a model in which the variation among GRBs is due to a variation in jet-opening angles, and find that the narrowest jets have the fastest outflows. We also explore models in which the jets have similar morphology and size, and the variation among bursts is caused by variation in viewing angle and/or due to a velocity profile. The relations between luminosity, variability, spectral lag and jet-break time can be qualitatively understood from models in which the Lorentz factor decreases as a function of angle from the jet axis. One expects to see high luminosities, short pulse lags and high variability as well as an early jet-break time for bursts viewed on axis, while higher viewing inclinations will yield lower luminosities, longer pulse lags, smoother bursts and later jet-break times.Comment: 10 pages, 3 figures, accepted to ApJ (new version contains minor changes

Grossman’s Missing Health Threshold

We present a generalized solution to Grossman’s model of health capital (1972), relaxing the widely used assumption that individuals can adjust their health stock instantaneously to an “optimal” level without adjustment costs. The Grossman model then predicts the existence of a health threshold above which individuals do not demand medical care. Our generalized solution addresses a significant criticism: the model’s prediction that health and medical care are positively related is consistently rejected by the data. We suggest structural and reduced form equations to test our generalized solution and contrast the predictions of the model with the empirical literature.health, demand for health, health capital, medical care, labor

On the role of extinction in failed gamma-ray burst optical/IR afterglows

While all but one Gamma-Ray Bursts observed in the X-ray band showed an X-ray afterglow, about 60 per cent of them have not been detected in the optical band. We demonstrate that in many cases this is not due to adverse observing conditions, or delay in performing the observations. We also show that the optically non-detected afterglows are not affected by particularly large Galactic absorbing columns, since its distribution is similar for both the detected and non-detected burst subclasses. We then investigate the hypothesis that the failure of detecting the optical afterglow is due to absorption at the source location. We find that this is a marginally viable interpretation, but only if the X-ray burst and afterglow emission and the possible optical/UV flash do not destroy the dust responsible for absorption in the optical band. If dust is efficiently destroyed, we are led to conclude that bursts with no detected optical afterglow are intrinsically different. Prompt infrared observations are the key to solve this issue.Comment: Accepted for publication in MNRAS, changes in the tables and in the statistical analysi

Met melkvee rondtrekken in natuurgebieden

Met welk vee kunnen we natuurdoelen op een rendabele manier realiseren? Vaak wordt jongvee of vleesvee gebruikt voor beheer van natuurgebieden. Melkvee vergt meer werk, maar is economisch aantrekkelijker, mits niet geïnvesteerd hoeft te worden in melkquotum. De economische resultaten van extensief beheer met melkvee zijn in 2 tabellen weergegeve

Workshop over “Vee in balans” levert veel discussie op

Eiwitrijke brok is overbodig, een hoge productie per koe is niet rendabel, minder beweiden is ook niet nodig om te voldoen aan de Minas-eindnormen van 2003 en tevens een goed saldo te realiseren. Ook de angst dat vee te weinig sporenelementen krijgt, zoals selenium of koper, is niet terecht. Deze boodschap werd uitgedragen tijdens de workshop “Vee in balans”. De middag was een vervolg op het symposium“Melkers van morgen” op 14 mei 2003 en bedoeld voor deskundigen van de mengvoerindustrie, voorlichting, dierenartspraktijken, gezondheidsdiensten, faculteit diergeneeskunde en Koeien & Kansen boeren. Samen discussieerden zij over de cijfers van Koeien & Kansen