The dwarf planet Eris is a trans-Neptunian object with an orbital eccentricity of 0.44, an inclination of 44 degrees and a surface composition very similar to that of Pluto. It resides at present at ...95.7 astronomical units (1 AU is the Earth-Sun distance) from Earth, near its aphelion and more than three times farther than Pluto. Owing to this great distance, measuring its size or detecting a putative atmosphere is difficult. Here we report the observation of a multi-chord stellar occultation by Eris on 6 November 2010 UT. The event is consistent with a spherical shape for Eris, with radius 1,163 ± 6 kilometres, density 2.52 ± 0.05 grams per cm(3) and a high visible geometric albedo, Pv = 0.96(+0.09)(-0.04). No nitrogen, argon or methane atmospheres are detected with surface pressure larger than ∼1 nanobar, about 10,000 times more tenuous than Pluto's present atmosphere. As Pluto's radius is estimated to be between 1,150 and 1,200 kilometres, Eris appears as a Pluto twin, with a bright surface possibly caused by a collapsed atmosphere, owing to its cold environment. We anticipate that this atmosphere may periodically sublimate as Eris approaches its perihelion, at 37.8 astronomical units from the Sun.
We have gathered optical photometry data from the literature on a large sample of Swift-era gamma-ray burst (GRB) afterglows including GRBs up to 2009 September, for a total of 76 GRBs, and present ...an additional three pre-Swift GRBs not included in an earlier sample. Furthermore, we publish 840 additional new photometry data points on a total of 42 GRB afterglows, including large data sets for GRBs 050319, 050408, 050802, 050820A, 050922C, 060418, 080413A, and 080810. We analyzed the light curves of all GRBs in the sample and derived spectral energy distributions for the sample with the best data quality, allowing us to estimate the host-galaxy extinction. We transformed the afterglow light curves into an extinction-corrected z = 1 system and compared their luminosities with a sample of pre-Swift afterglows. The results of a former study, which showed that GRB afterglows clustered and exhibited a bimodal distribution in luminosity space, are weakened by the larger sample. We found that the luminosity distribution of the two afterglow samples (Swift-era and pre-Swift) is very similar, and that a subsample for which we were not able to estimate the extinction, which is fainter than the main sample, can be explained by assuming a moderate amount of line-of-sight host extinction. We derived bolometric isotropic energies for all GRBs in our sample, and found only a tentative correlation between the prompt energy release and the optical afterglow luminosity at 1 day after the GRB in the z = 1 system. A comparative study of the optical luminosities of GRB afterglows with echelle spectra (which show a high number of foreground absorbing systems) and those without, reveals no indication that the former are statistically significantly more luminous. Furthermore, we propose the existence of an upper ceiling on afterglow luminosities and study the luminosity distribution at early times, which was not accessible before the advent of the Swift satellite. Most GRBs feature afterglows that are dominated by the forward shock from early times on. Finally, we present the first indications of a class of long GRBs, which form a bridge between the typical high-luminosity, high-redshift events and nearby low-luminosity events (which are also associated with spectroscopic supernovae) in terms of energetics and observed redshift distribution, indicating a continuous distribution overall.
We present a comprehensive analysis of a bright, long-duration (T sub(90) ~ 257 s) GRB 110205A at redshift z = 2.22. The optical prompt emission was detected by Swift/UVOT, ROTSE-IIIb, and BOOTES ...telescopes when the gamma-ray burst (GRB) was still radiating in the gamma -ray band, with optical light curve showing correlation with gamma -ray data. Nearly 200 s of observations were obtained simultaneously from optical, X-ray, to gamma -ray (1 eV to 5 MeV), which makes it one of the exceptional cases to study the broadband spectral energy distribution during the prompt emission phase. In particular, we clearly identify, for the first time, an interesting two-break energy spectrum, roughly consistent with the standard synchrotron emission model in the fast cooling regime. Shortly after prompt emission (~1100 s), a bright (R = 14.0) optical emission hump with very steep rise ( alpha ~ 5.5) was observed, which we interpret as the reverse shock (RS) emission. It is the first time that the rising phase of an RS component has been closely observed. The full optical and X-ray afterglow light curves can be interpreted within the standard reverse shock (RS) + forward shock (FS) model. In general, the high-quality prompt and afterglow data allow us to apply the standard fireball model to extract valuable information, including the radiation mechanism (synchrotron), radius of prompt emission (R sub(GRB) ~ 3 x 10 super(13) cm), initial Lorentz factor of the outflow (Gamma sub(0) ~ 250), the composition of the ejecta (mildly magnetized), the collimation angle, and the total energy budget.
Gamma-ray bursts (GRBs) and their afterglows are the most brilliant transient events in the Universe. Both the bursts themselves and their afterglows have been predicted to be visible out to ...redshifts of z 20, and therefore to be powerful probes of the early Universe. The burst GRB 000131, at z = 4.50, was hitherto the most distant such event identified. Here we report the discovery of the bright near-infrared afterglow of GRB 050904 (ref. 4). From our measurements of the near-infrared afterglow, and our failure to detect the optical afterglow, we determine the photometric redshift of the burst to be z = 6.39 - 0.12 + 0.11 (refs 5-7). Subsequently, it was measured spectroscopically to be z = 6.29 ± 0.01, in agreement with our photometric estimate. These results demonstrate that GRBs can be used to trace the star formation, metallicity, and reionization histories of the early Universe.
In thick fully depleted CCDs charge carrier transport from the back window to the gates is accompanied by charge diffusion. Lateral diffusion smooths out density variations of the incoming photon ...flux by redistributing charges spatially. This creates short range positive correlations in recorded amplitudes. Pixel-to-pixel amplitude variations can also be caused by pixel size and quantum efficiency variations. Pixel size variations result in short range negative correlations. Our study shows that the characteristic diffusion width can be extracted from flat field data.
The study was performed on fully depleted, thick CCDs produced in a technology study for the Large Synoptic Survey Telescope (LSST). Data were taken in the laboratory at bias voltages between −5 and −40
V. To increase statistical accuracy, images taken in identical conditions were co-added after base line subtraction and master files were produced. A flat field image simulator was developed for statistical comparison of simulated and measured images.
Results on diffusion, pixel response variations, data features, analysis and modeling techniques are presented and discussed.
We use a sample of 19 gamma-ray bursts (GRBs) that exhibit single-peaked optical light curves to test the standard fireball model by investigating the relationship between the time of the onset of ...the afterglow and the temporal rising index. Our sample includes GRBs and X-ray flashes for which we derive a wide range of initial Lorentz factors (40 < Delta *G < 450). Using plausible model parameters, the typical frequency of the forward shock is expected to lie close to the optical band; within this low typical frequency framework, we use the optical data to constrain e and show that values derived from the early time light-curve properties are consistent with published typical values derived from other afterglow studies. We produce expected radio light curves by predicting the temporal evolution of the expected radio emission from forward and reverse shock components, including synchrotron self-absorption effects at early time. Although a number of GRBs in this sample do not have published radio measurements, we demonstrate the effectiveness of this method in the case of Swift GRB 090313, for which millimetric and centimetric observations were available, and conclude that future detections of reverse-shock radio flares with new radio facilities such as the EVLA and ALMA will test the low-frequency model and provide constraints on magnetic models.
DG Canum Venaticorum (DG CVn) is a binary system in which one of the components is an M-type dwarf ultrafast rotator, only three of which are known in the solar neighbourhood. Observations of DG CVn ...by the Swift satellite and several ground-based observatories during its superflare event on 2014 allowed us to perform a complete hard X-ray–optical follow-up of a superflare from the red-dwarf star. The observations support the fact that the superflare can be explained by the presence of (a) large active region(s) on the surface of the star. Such activity is similar to the most extreme solar flaring events. This points towards a plausible extrapolation between the behaviour from the most active red-dwarf stars and the processes occurring in the Sun.
Long γ-ray bursts (GRBs) are the most dramatic examples of massive stellar deaths, often associated with supernovae. They release ultra-relativistic jets, which produce non-thermal emission through ...synchrotron radiation as they interact with the surrounding medium. Here we report observations of the unusual GRB 101225A. Its γ-ray emission was exceptionally long-lived and was followed by a bright X-ray transient with a hot thermal component and an unusual optical counterpart. During the first 10 days, the optical emission evolved as an expanding, cooling black body, after which an additional component, consistent with a faint supernova, emerged. We estimate its redshift to be z = 0.33 by fitting the spectral-energy distribution and light curve of the optical emission with a GRB-supernova template. Deep optical observations may have revealed a faint, unresolved host galaxy. Our proposed progenitor is a merger of a helium star with a neutron star that underwent a common envelope phase, expelling its hydrogen envelope. The resulting explosion created a GRB-like jet which became thermalized by interacting with the dense, previously ejected material, thus creating the observed black body, until finally the emission from the supernova dominated. An alternative explanation is a minor body falling onto a neutron star in the Galaxy.
FTIR spectroscopy in transmission mode combined with a focal plane array (FPA) detector was employed for parallel characterization of Pt-containing zeolites ZSM-5 and Y. The different Pt species in ...the zeolite were investigated using the chemisorption of carbon monoxide. With the new transmission setup, 8-fold degree of parallelization was achieved. This significantly lowered the total time required for collection of the desired information from a set of samples. The optical setup based on FPA-IR detection provides data of high reliability. For the discussion of the individual IR band assignment, TEM analysis data are included to corroborate the conclusions.
ABSTRACT
The Swift era has posed a challenge to the standard blast‐wave model of gamma‐ray burst (GRB) afterglows. The key observational features expected within the model are rarely observed, such ...as the achromatic steepening (‘jet break’) of light curves. The observed afterglow light curves showcase additional complex features requiring modifications within the standard model. Here we present optical/near‐infrared observations, millimetre upper limits and comprehensive broad‐band modelling of the afterglow of the bright GRB 0505025A, detected by Swift. This afterglow cannot be explained by the simplistic form of the standard blast‐wave model. We attempt modelling multiwavelength light curves using (i) a forward–reverse shock model, (ii) a two‐component outflow model and (iii) a blast‐wave model with a wind termination shock. The forward–reverse shock model cannot explain the evolution of the afterglow. The two‐component model is able to explain the average behaviour of the afterglow very well but cannot reproduce the fluctuations in the early X‐ray light curve. The wind termination shock model reproduces the early light curves well but deviates from the global behaviour of the late‐time afterglow.
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