Search results for "Galaxy Astrophysics"
showing 10 items of 1297 documents
Process-based microphysical characterization of a strong mid-latitude convective system using aircraft in situ cloud measurements
2022
Clouds in the mixed-phase temperature regime impose a large uncertainty onto climate prediction models, in part due to incomplete knowledge of the degree of glaciation affecting cloud radiative properties. To achieve a better representation of these clouds, it is crucial to improve the understanding of ice nucleation and growth as well as microphysical properties determining the cloud phase. In this case study, we provide a rare data set of aircraft in situ measurements in a strong mid-latitude convective system extending from the boundary layer to the tropopause and aim to extend the sparse database of such measurements. Data were obtained with the research aircraft HALO and cloud properti…
The B0.5IVe CoRoT target HD 49 330. I. Photometric analysis from CoRoT data
2009
Context. Be stars undergo outbursts producing a circumstellar disk from the ejected material. The beating of non-radial pulsations has been put forward as a possible mechanism of ejection. Aims. We analyze the pulsational behavior of the early B0.5IVe star HD 49330 observed during the first CoRoT long run towards the Galactical anticenter (LRA1). This Be star is located close to the lower edge of the β Cephei instability strip in the HR diagram and showed a 0.03 mag outburst during the CoRoT observations. It is thus an ideal case for testing the aforementioned hypothesis. Methods. We analyze the CoRoT light curve of HD 49330 usin g Fourier methods and non-lin ear least square fitting. Resul…
The ALHAMBRA Project: A large area multi medium-band optical and NIR photometric survey
2008
(ABRIDGED) We describe the first results of the ALHAMBRA survey which provides cosmic tomography of the evolution of the contents of the Universe over most of Cosmic history. Our approach employs 20 contiguous, equal-width, medium-band filters covering from 3500 to 9700 A, plus the JHKs bands, to observe an area of 4 sqdeg on the sky. The optical photometric system has been designed to maximize the number of objects with accurate classification by SED and redshift, and to be sensitive to relatively faint emission lines. The observations are being carried out with the Calar Alto 3.5m telescope using the cameras LAICA and O-2000. The first data confirm that we are reaching the expected magnit…
On the existence of a reverse shock in magnetized GRB ejecta
2007
The role of magnetic fields in gamma-ray burst (GRB) flows remains controversial. The study of the early afterglow phases and, in particular, of the reverse shock dynamics and associated emission offers a promising probe of the magnetization of the ejecta. In this paper, we derive the conditions for the existence of a reverse shock in arbitrarily magnetized ejecta that decelerate and interact with the circumburst medium. Both constant and wind-like density profiles are considered. We show, in contrast to previous estimates, that ejecta with magnetization larger than unity are not crossed by a reverse shock for a large fraction of the parameter space relevant to GRB flows. Allowing for shell…
Swift GRBs: The early afterglow spectral energy distribution
2007
We present the first results of a program to systematically study the optical-to-X-ray spectral energy distribution (SED) of Swift GRB afterglows with known redshift. The goal is to study the properties of the GRB explosion and of the intervening absorbing material. In this report we present the preliminary analysis on 23 afterglows. Thanks to Swift, we could build the SED at early times after the GRB (minutes to hours). We derived the Hydrogen column densities and the spectral slopes from the X-ray spectrum. We then constrained the visual extinction by requiring that the combined optical/X-ray SED is due to synchrotron, namely either a single power law or a broken power law with a slope ch…
INTEGRAL monitoring of the Black Hole candidate 1E 1740.7-2942
2004
The brightest persistent Galactic black hole candidate close to the Galactic Centre, 1E 1740.7-2942, has long been observed with INTEGRAL. In this paper, we report on the long-term hard X-ray monitoring obtained during the first year of observations as part of the Galactic Centre Deep Exposure. We discuss the temporal and spectral behaviours in different energy bands up to 250 keV, as well as the hardness-flux correlations.
VLBI Observations of a Complete Sample of Radio Galaxies V. 3C346 and 4C31.04: two Unusual CSS Sources
1995
We present observations at 1.7 and 8.4 GHz of two Compact Steep Spectrum (CSS) sources from a complete sample of low-intermediate power radio galaxies. 3C346 shows an asymmetric structure with a one-sided ``jet'' and ``hot spot''. Present observations suggest that the classification of this source as a CSS is inappropriate, and that it is a common radio galaxy at a small angle to the line of sight. Its properties are in agreement with the predictions of unified schemes models. 4C31.04 shows more complex structure with the possibility of a centrally located flat spectrum core in between two close lobes. We suggest that this source could be a low redshift Compact Symmetric Object.
The short GRB 051210 observed by Swift
2007
We report on the short GRB051210 detected by the Swift-BAT. The light curve, on which we focus mainly, shows a hint of extended emission in the BAT energy range, a steep decay of the X-ray emission, without any flattening or break, and two small flares in the first 300 sec. The emission fades out after ~1000 s.
How is really decelerating the expansion of SN1993J?
2002
SN1993J is to date the radio supernova whose evolution has been monitored in greatest detail and the one which holds best promise for a comprehensive theoretical-observational analysis. The shell-like radio structure of SN1993J has expanded in general accord with models of shock excited emission, showing almost circular symmetry for over 8 years, except for a bright feature at the south-eastern region of the shell that has been observed at every epoch. The spectrum of SN1993J has flattened from alpha =-1 to alpha =-0.67 (S_(\nu) propto nu**(alpha)). The decelerated expansion can be modeled well with a single slope but apparently better with two slopes. There are also intriguing hints of str…
Bending relativistic jets in AGNs
1997
We present simulations of relativistic jets propagating in a nonuniform medium. Specifically, we study the bending of jets propagating obliquely to the vector of the density-gradient. Our results are applied to the NGC 4258, where such a medium is assumed to be provided by the atmosphere of the sub-parsec accretion disk tilted with respect to the original direction of the jet propagation. As a result, the jet is bent on a scale comparable to the density scaleheight of the disk atmosphere. The magnitude of the bending effect is found to be largest for light jets with low Lorentz factors. The predicted direction of bending is consistent with the observations.