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Over the past five years evidence has mounted that long-duration (>2 s) γ-ray bursts (GRBs)—the most luminous of all astronomical explosions—signal the collapse of massive stars in our Universe. This evidence was originally based on the probable association of one unusual GRB with a supernova 1 , but now includes the association of GRBs with regions of massive star formation in distant galaxies 2 , 3 , the appearance of supernova-like ‘bumps’ in the optical afterglow light curves of several bursts 4 , 5 , 6 and lines of freshly synthesized elements in the spectra of a few X-ray afterglows 7 . These observations support, but do not yet conclusively demonstrate, the idea that long-duration GRBs are associated with the deaths of massive stars, presumably arising from core collapse. Here we report evidence that a very energetic supernova (a hypernova) was temporally and spatially coincident with a GRB at redshift z = 0.1685. The timing of the supernova indicates that it exploded within a few days of the GRB, strongly suggesting that core-collapse events can give rise to GRBs, thereby favouring the ‘collapsar’ model 8 , 9 .

Summary Background In laboratory animals, cerebral ischaemia is worsened by hyperthermia and improved by hypothermia. Whether these observations apply to human beings with stroke is unknown. We therefore examined the relation between body temperature on admission with acute stroke and various indices of stroke severity and outcome. Methods In a prospective and consecutive study 390 stroke patients were admitted to hospital within 6 h after stroke (median 2·4 h). We determined body temperature on admission, initial stroke severity, infarct size, mortality, and outcome in survivors. Stroke severity was measured on admission, weekly, and at discharge on the Scandinavian Stroke Scale (SSS). Infarct size was determined by computed tomography. Multiple logistic and linear regression outcome analyses included relevant confounders and potential predictors such as age, gender, stroke severity on admission, body temperature, infections, leucocytosis, diabetes, hypertension, atrial fibrillation, ischaemic heart disease, smoking, previous stroke, and comorbidity. Findings Mortality was lower and outcome better in patients with mild hypothermia on admission; both were worse in patients with hyperthermia. Body temperature was independently related to initial stroke severity (p<0·009), infarct size (p<0·0001), mortality (p<0·02), and outcome in survivors (SSS at discharge) (p<0·003). For each 1°C increase in body temperature the relative risk of poor outcome (death or SSS score on discharge <30 points) rose by 2·2 (95% Cl 1·4-3·5) (p<0·002). Interpretation We have shown that, in acute human stroke, an association exists between body temperature and initial stroke severity, infarct size, mortality, and outcome. Only intervention trials of hypothermic treatment can prove whether this relation is causal.

. Metallicity gradients are most frequently investigated directly from galaxies observed in emission. We have shown that galaxies detected via strong quasar absorption lines also exhibits a metallicity gradient in the outskirts and circumgalactic medium out to ~40 kpc distance. We infer a metallicity gradient of −0.022 dex kpc−1 for absorption-selected systems at redshifts 0.1 z 3. Applying this metallicity gradient and a flattening of the gradient beyond 12 kpc, we demonstrate that absorption-selected galaxies obey the same mass-metallicity relation (MZR) as observed for luminosity-selected galaxies.

ESO’s two FOcal Reducer and low-dispersion Spectrographs (FORS) are the primary optical imaging instruments for the VLT. They are not direct-imaging instruments, as there are several optical elements in the light path. In particular, both instruments are attached to a field rotator. Obtaining truly photometric data with such instruments presents a significant challenge. In this article, we investigate in detail twilight flats taken with the FORS instruments. We find that a large fraction of the structure seen in these flat fields rotates with the field rotator. We discuss in detail the methods we use to determine the cause of this effect. The effect was tracked down to be caused by the Linear Atmospheric Dispersion Corrector (LADC). The results are thus of special interest for designers of instruments with LADCs and developers of calibration plans and pipelines for such instruments. The methods described here to find and correct it, however, are of interest also for other instruments using a field rotator. If not properly corrected, this structure in the flat field may degrade the photometric accuracy of imaging observations taken with the FORS instruments by adding a systematic error of up to 4% for broadband filters. We discuss several strategies to obtain photometric images in the presence of rotating flat-field pattern.

Quasars are the visible signatures of gas falling into the deep potential well of super-massive black holes in the centres of distant galaxies. It has been suggested 1 that quasars are formed when two massive galaxies collide and merge, leading to the prediction that quasars should be found in the centres of regions of largest overdensity in the early Universe. In dark matter (DM)-dominated models of the early Universe, massive DM halos are predicted to attract the surrounding gas, which falls towards their centres. The neutral gas is not detectable in emission by itself, but gas falling into the ionizing cone of such a quasar will glow in the Lyman-α line of hydrogen, effectively imaging the DM halo 2 . Here we present a Lyα image of a DM halo at redshift z = 3, along with a two-dimensional spectrum of the gaseous halo. Our observations are best understood in the context of the standard model for DM haloes 3 ; we infer a mass of (2 - 7) × 10 12 solar masses ( M ⊙ ) for the halo.

To determine the types, severity and evolution of aphasia in unselected, acute stroke patients and evaluate potential predictors for language outcome 1 year after stroke. 270 acute stroke patients with aphasia (203 with first-ever strokes) were included consecutively and prospectively from three hospitals in Copenhagen, Denmark, and assessed with the Western Aphasia Battery. The assessment was repeated 1 year after stroke. The frequencies of the different types of aphasia in acute first-ever stroke were: global 32%, Broca's 12%, isolation 2%, transcortical motor 2%, Wernicke's 16%, transcortical sensory 7%, conduction 5% and anomic 25%. These figures are not substantially different from what has been found in previous studies of more or less selected populations. The type of aphasia always changed to a less severe form during the first year. Nonfluent aphasia could evolve into fluent aphasia (e.g., global to Wernicke's and Broca's to anomic), whereas a fluent aphasia never evolved into a nonfluent aphasia. One year after stroke, the following frequencies were found: global 7%, Broca's 13%, isolation 0%, transcortical motor 1%, Wernicke's 5%, transcortical sensory 0%, conduction 6% and anomic 29%. The distribution of aphasia types in acute and chronic aphasia is, thus, quite different. The outcome for language function was predicted by initial severity of the aphasia and by the initial stroke severity (assessed by the Scandinavian Stroke Scale), but not by age, sex or type of aphasia. Thus, a scoring of general stroke severity helps to improve the accuracy of the prognosis for the language function. One year after stroke, fluent aphasics were older than nonfluent aphasics, whereas such a difference was not found in the acute phase.

An optical spectrum of the afterglow from the unusually bright gamma-ray burst GRB 990123 obtained on 24.25 January 1999 universal time showed an absorption system at a redshift of z = 1.600. The absence of a hydrogen Lyman α forest sets an upper limit of z < 2.17, whereas ultraviolet photometry indicates an upper limit of z < 2.05. The probability of intersecting an absorption system as strong as the one observed along a random line of sight out to this z is at most a few percent, implying that GRB 990123 was probably at z = 1.600. Currently favored cosmological parameters imply that an isotropic energy release equivalent to the rest mass of 1.8 neutron stars (4.5 × 10$^{54}$ erg) was emitted in gamma rays. Nonisotropic emission, such as intrinsic beaming, may resolve this energy problem.

Aim: To determine the types, severity and evolution of aphasia in unselected, acute stroke patients and evaluate potential predictors for language outcome 1 year after stroke. Methods: 270 acute stroke patients with aphasia (203 with first-ever strokes) were included consecutively and prospectively from three hospitals in Copenhagen, Denmark, and assessed with the Western Aphasia Battery. The assessment was repeated 1 year after stroke. Results: The frequencies of the different types of aphasia in acute first-ever stroke were: global 32%, Broca’s 12%, isolation 2%, transcortical motor 2%, Wernicke’s 16%, transcortical sensory 7%, conduction 5% and anomic 25%. These figures are not substantially different from what has been found in previous studies of more or less selected populations. The type of aphasia always changed to a less severe form during the first year. Nonfluent aphasia could evolve into fluent aphasia (e.g., global to Wernicke’s and Broca’s to anomic), whereas a fluent aphasia never evolved into a nonfluent aphasia. One year after stroke, the following frequencies were found: global 7%, Broca’s 13%, isolation 0%, transcortical motor 1%, Wernicke’s 5%, transcortical sensory 0%, conduction 6% and anomic 29%. The distribution of aphasia types in acute and chronic aphasia is, thus, quite different. The outcome for language function was predicted by initial severity of the aphasia and by the initial stroke severity (assessed by the Scandinavian Stroke Scale), but not by age, sex or type of aphasia. Thus, a scoring of general stroke severity helps to improve the accuracy of the prognosis for the language function. One year after stroke, fluent aphasics were older than nonfluent aphasics, whereas such a difference was not found in the acute phase.

The MZ relation between stellar mass (M*) and metallicity (Z) of nearby galaxies has been described as both a global and local property, i.e. valid also on sub-galaxy scales. Here we show that Z has remained a local property, following the gravitational potential, since z=3. In absorption the MZ relation has been well studied, and was in place already at z=5.1. A recent absorption study of GRB galaxies revealed a close match to Damped Ly{\\alpha} (DLA) galaxies, surprising due to their vastly different impact parameters and leading the authors to suggest that local metallicity follows the local gravitational potential. In this paper we formulate an observational test of this hypothesis. The test, in essence, forms a prediction that the velocity dispersion of the absorbing gas in galaxy halos, normalized by the central velocity dispersion, must follow a steep log scale slope of -0.015 dex/kpc as a function of impact parameter out to at least 20-30 kpc. We then compile an archival data and literature based sample of galaxies seen in both emission and absorption suitable for the test, and find that current data confirm the hypothesis out to 40-60 kpc. In addition we show that the distribution of the velocity offsets between z em and z abs favours a model where DLA systems are composed of individual sub-clouds distributed along the entire path through the halo, and disfavours a model where they are one single cloud with a bulk motion and internal sub-structure.

Dust plays a pivotal role in the chemical enrichment of the interstellar medium. In the era of mid/high resolution spectra and multi-band spectral energy distributions, testing extinctions against gas and dust-phase properties is becoming possible. In order to test relations between metals, dust and depletions, and comparing those to the Local Group (LG) relations, we build a sample of 93 gamma-ray bursts and quasar absorbers (the largest sample so far) which have extinction and elemental column density measurements available. We find that extinctions and total column density of the volatile elements (Zn, S) are correlated (with a best-fit of dust-to-metals (DTM) 4.05x10-22 mag cm2) and consistent with the LG DTM relation. The refractory elements (Fe, Si) follow a similar, but less significant, relation offset about 1 dex from the LG relation. On the assumption that depletion onto dust grains is the cause, we compute the total (gas+dust-phase) column density and find a remarkable agreement with the LG DTM relation: a best-fit of 4.91x10-22 mag cm2. We then use our results to compute the amount of 'intervening metal from unknown sources' in random sightlines out to redshifts of z=5. Those metals implicate the presence of dust and give rise to an average 'cosmic dust dimming' effect which we express as a function of redshift, CDD(z). The CDD is unimportant out to redshifts of about 3, but because it is cumulative it becomes significant at redshifts z=3-5. Our results in this paper are based on a minimum of assumptions and effectively relying on observations.