2,912 research outputs found
The bright optical afterglow of the nearby gamma-ray burst of 29 March 2003
Many past studies of cosmological gamma-ray bursts (GRBs) have been limited
because of the large distance to typical GRBs, resulting in faint afterglows.
There has long been a recognition that a nearby GRB would shed light on the
origin of these mysterious cosmic explosions, as well as the physics of their
fireballs. However, GRBs nearer than z=0.2 are extremely rare, with an
estimated rate of localisation of one every decade. Here, we report the
discovery of bright optical afterglow emission from GRB 030329. Our prompt
dissemination and the brilliance of the afterglow resulted in extensive
followup (more than 65 telescopes) from radio through X-ray bands, as well as
measurement of the redshift, z=0.169. The gamma-ray and afterglow properties of
GRB 030329 are similar to those of cosmological GRBs (after accounting for the
small distance), making this the nearest known cosmological GRB. Observations
have already securely identified the progenitor as a massive star that exploded
as a supernova, and we anticipate futher revelations of the GRB phenomenon from
studies of this source.Comment: 13 pages, 4 figures. Original tex
Veterinary Conduct and Animal Welfare
This paper is a lecture presented to the same Association but fifteen years later: the 131st Annual Congress in 1984. This second presentation contemplates two points: First, it tries to indicate how this criticism has gradually emerged and a historical outline is put forth of the development of veterinary medicine, a differentiation being made between a mythical, a technical, and a critical approach. Second, a discussion of how veterinarians have to associate themselves with this criticism in their professional conduct is presented. This discussion is necessary for two reasons. Veterinarians have increasingly become aware that they bear a professional responsibility not only for animal health but also for animal welfare; and, veterinarians are expected to give their views in concrete situations
An integrated concurrency and core-ISA architectural envelope definition, and test oracle, for IBM POWER multiprocessors
Funding: Scottish Funding Council (SICSA Early Career Industry Fellowship)Weakly consistent multiprocessors such as ARM and IBM POWER have been with us for decades, but their subtle programmer-visible concurrency behaviour remains challenging, both to implement and to use; the traditional architecture documentation, with its mix of prose and pseudocode, leaves much unclear. In this paper we show how a precise architectural envelope model for such architectures can be defined, taking IBM POWER as our example. Our model specifies, for an arbitrary test program, the set of all its allowable executions, not just those of some particular implementation. The model integrates an operational concurrency model with an ISA model for the fixedpoint non-vector user-mode instruction set (largely automatically derived from the vendor pseudocode, and expressed in a new ISA description language). The key question is the interface between these two: allowing all the required concurrency behaviour, without overcommitting to some particular microarchitectural implementation, requires a novel abstract structure. Our model is expressed in a mathematically rigorous language that can be automatically translated to an executable test-oracle tool; this lets one either interactively explore or exhaustively compute the set of all allowed behaviours of intricate test cases, to provide a reference for hardware and software development.Postprin
Discovery of Early Optical Emission from GRB 021211
We report our discovery and early time optical, near-infrared, and radio
wavelength follow-up observations of the afterglow of the gamma-ray burst GRB
021211. Our optical observations, beginning 21 min after the burst trigger,
demonstrate that the early afterglow of this burst is roughly three magnitudes
fainter than the afterglow of GRB 990123 at similar epochs, and fainter than
almost all known afterglows at an epoch of 1d after the GRB. Our near-infrared
and optical observations indicate that this is not due to extinction. Combining
our observations with data reported by other groups, we identify the signature
of a reverse shock. This reverse shock is not detected to a 3-sigma limit of
110 uJy in an 8.46-GHz VLA observation at t=0.10d, implying either that the
Lorentz factor of the burst gamma <~ 200, or that synchrotron self-absorption
effects dominate the radio emission at this time. Our early optical
observations, near the peak of the optical afterglow (forward shock), allow us
to characterize the afterglow in detail. Comparing our model to flux upper
limits from the VLA at later times, t >~ 1 week, we find that the late-time
radio flux is suppressed by a factor of two relative to the >~ 80 uJy peak flux
at optical wavelengths. This suppression is not likely to be due to synchrotron
self-absorption or an early jet break, and we suggest instead that the burst
may have suffered substantial radiative corrections.Comment: 13 pages, 2 figures, ApJL accepted; edits for lengt
The Broadband Afterglow of GRB980329
We present radio observations of the afterglow of the bright gamma-ray burst
GRB980329 made between one month and several years after the burst, a
re-analysis of previously published submillimeter data, and late-time optical
and near-infrared (NIR) observations of the host galaxy. From the absence of a
spectral break in the optical/NIR colors of the host galaxy, we exclude the
earlier suggestion that GRB980329 lies at a redshift of z >~5. We combine our
data with the numerous multi-wavelength observations of the early afterglow,
fit a comprehensive afterglow model to the entire broadband dataset, and derive
fundamental physical parameters of the blast-wave and its host environment.
Models for which the ejecta expand isotropically require both a high
circumburst density and extreme radiative losses from the shock. No low density
model (n << 10 cm^{-3}) fits the data. A burst with a total energy of ~ 10^{51}
erg, with the ejecta narrowly collimated to an opening angle of a few degrees,
driven into a surrounding medium with density ~ 20 cm^{-3}, provides a
satisfactory fit to the lightcurves over a range of redshifts.Comment: 27 pages, incl. 6 figures, minor revisions (e.g. added/updated
references) Accepted by Ap
COP21 climate negotiators' responses to climate model forecasts
Policymakers involved in climate change negotiations are key users of climate science. It is therefore vital to understand how to communicate scientific information most effectively to this group. We tested how a unique sample of policymakers and negotiators at the Paris COP21 conference update their beliefs on year 2100 global mean temperature increases in response to a statistical summary of climate models' forecasts. We randomized the way information was provided across participants using three different formats similar to those used in Intergovernmental Panel on Climate Change reports. In spite of having received all available relevant scientific information, policymakers adopted such information very conservatively, assigning it less weight than their own prior beliefs. However, providing individual model estimates in addition to the statistical range was more effective in mitigating such inertia. The experiment was repeated with a population of European MBA students who, despite starting from similar priors, reported conditional probabilities closer to the provided models' forecasts than policymakers. There was also no effect of presentation format in the MBA sample. These results highlight the importance of testing visualization tools directly on the population of interest
Detection of a supernova signature associated with GRB 011121
Using observations from an extensive monitoring campaign with the Hubble
Space Telescope we present the detection of an intermediate-time flux excess
which is redder in color relative to the afterglow of GRB 011121, currently
distinguished as the gamma-ray burst with the lowest known redshift. The red
``bump,'' which exhibits a spectral roll-over at ~7200 Angstrom, is well
described by a redshifted Type Ic supernova that occurred approximately at the
same time as the gamma-ray burst event. The inferred luminosity is about half
that of the bright supernova 1998bw. These results serve as compelling evidence
for a massive star origin of long-duration gamma-ray bursts. Models that posit
a supernova explosion weeks to months preceding the gamma-ray burst event are
excluded by these observations. Finally, we discuss the relationship between
spherical core-collapse supernovae and gamma-ray bursts.Comment: Published in the Astrophysical Journal (Letters) on 20 May 2002.
Seven LaTeX pages, three Postscript figures, one tabl
GRB 011121: A Massive Star Progenitor
Of the cosmological gamma-ray bursts, GRB 011121 has the lowest redshift, z = 0.36. More importantly, the multicolor excess in the afterglow detected in the Hubble Space Telescope (HST) light curves is compelling observational evidence of an underlying supernova. Here we present near-infrared and radio observations of the afterglow, and from our comprehensive afterglow modeling, we find evidence favoring a wind-fed circumburst medium. Lacking X-ray data, we are unable to conclusively measure the mass-loss rate, M, but obtain an estimate, M ~ 2 Ă 10^(-7)/vw_3 Mâ yr^(-1), where vw_3 is the speed of the wind from the progenitor in units of 10^3 km s^(-1). This M is similar to that inferred for the progenitor of the Type Ibc supernova SN 1998bw that has been associated with the peculiar burst GRB 980425. Our data, taken in conjunction with the HST results of Bloom et al., provide a consistent picture: the long-duration GRB 011121 had a massive star progenitor that exploded as a supernova at about the same time as the gamma-ray burst event. Finally, we note that the gamma-ray profile of GRB 011121 is similar to that of GRB 980425
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