246 research outputs found
X-Ray Afterglows of Gamma-Ray Bursts
The afterglow emission has become the main stream of Gamma-Ray burst research
since its discovery three years ago. With the distance-scale enigma solved, the
study of the late-time GRB emission is now the most promising approach to
disclose the origin of these explosions and their relationship with the
environment of the host galaxy in the early phase of the Universe. In this
contribution I will review X-ray observations and their implication on our
undertstanding on the GRB phenomenon. These measurements are providing a direct
probe into the nature of the progenitor and a measurement of the GRB beaming
properties, crucial to establish the total energy output. Some evidence of iron
lines connects the GRB explosion with massive progenitors, thence with
star-forming regions. Furthermore a comparison of the spectral properties with
the temporal evolution indicates that the fireball expansion should not be - on
average - highly collimated, with a jet angle .Comment: 14 pages, 8 figures, Proc.s. of "X-Ray Astronomy '99:Stellar
Endpoints, AGN and the Diffuse X-ray Background", September 6-10, 1999, CNR
Bologn
Global properties of X-ray afterglows of GRB
In this paper we review the general properties of X-ray afterglows. We
discuss in particular on the powerful diagnostics provided by X-ray afterglows
in constraining the environment and fireball in normal GRB, and the
implications on the origin of dark GRB and XRF. We also discuss on the observed
properties of the transition from the prompt to the afterglow phase, and
present a case study for a late X-ray outburst interpreted as the onset of the
afterglow stage.Comment: 8 pages, 1 color figure. Accepted for publication in "il nuovo
cimento". Proceeding of the 4th Rome GRB conference, eds. L. Piro, L. Amati,
S. Covino, B. Gendre. Corrected a typo in caption of Fig.
2D and 3D data processing of archaeo-magnetic data
Introduction. The Sabine Necropolis at Colle del Forno (700-300 B.C.) at Montelibretti, Rome is characterized by dromos chamber tombs, most of them unexplored till now. The tombs can be assimilated to cavities of a standard volume of some cubic meters; the entrance of the tombs is a corridor 6 m long with a 1 square meter section . The surficial geology of the area consists of a series of tuffs about 10 m thick overlying Pleistocene-Quaternary sandy-clayey sediments. A thin layer of top soil (20 - 30 cm) covers the tuff. The investigation of the Necropolis in the past decade has been performed by different geophysical methodologies: electrical, electromagnetic and magnetic methods have been widely adopted to investigate several chamber tombs (Piro et al, 2001). The aim of this paper is to analyze an integrated approach to the processing of magnetic survey data. The magnetic susceptibility contrast between topsoil, subsoil and rocks (topsoil is normally more magnetic than subsoil) permits to detect ditches, pits and other silted-up features that were excavated and then silted or back-filled with topsoil. Meanwhile back-filled areas produce positive anomalies, less magnetic material introduced into topsoil, including many kinds of masonry (for example, limestone walls) may produce negative anomalies of the order of some nanoteslas. The same behavior is related to the presence of cultural voids and tombs whose magnetic anomaly is generated by the lack of magnetic materials due to the cavities of the tombs. In the area a diffused magnetisation is manly due to the presence of top soil and tuff materials and high negative susceptibility contrasts can be expected because of the presence of the tombs. The magnetic survey was performed along a regular grid of 0.5 m x 0.5 m using a optical pumped Caesium-vapour magnetometer G858 (Geometrics), in the gradient configuration, on an area which is well known as far as the presence, size and position of tombs are concerne
The Cryogenic AntiCoincidence detector for ATHENA X-IFU: a scientific assessment of the observational capabilities in the hard X-ray band
ATHENA is a large X-ray observatory, planned to be launched by ESA in 2028
towards an L2 orbit. One of the two instruments of the payload is the X-IFU: a
cryogenic spectrometer based on a large array of TES microcalorimeters, able to
perform integral field spectrography in the 0.2-12 keV band (2.5 eV FWHM at 6
keV). The X-IFU sensitivity is highly degraded by the particle background
expected in the L2 orbit, which is induced by primary protons of both galactic
and solar origin, and mostly by secondary electrons. To reduce the particle
background level and enable the mission science goals, the instrument
incorporates a Cryogenic AntiCoincidence detector (CryoAC). It is a 4 pixel TES
based detector, placed <1 mm below the main array. In this paper we report a
scientific assessment of the CryoAC observational capabilities in the hard
X-ray band (E>10 keV). The aim of the study has been to understand if the
present detector design can be improved in order to enlarge the X-IFU
scientific capability on an energy band wider than the TES array. This is
beyond the CryoAC baseline, being this instrument aimed to operate as
anticoincidence particle detector and not conceived to perform X-ray
observations.Comment: Accepted for publication on Experimental Astronom
X-Ray Spectroscopy of Gamma-Ray Bursts
Observational evidence of iron absorption and emission lines in X-ray spectra
of Gamma-Ray Bursts is quite compelling. I will briefly review the results,
summarize different models and describe the connection with massive progenitors
in star-forming regions implied by these results. This link is also supported
by measurements of the X-ray absorbing gas in several GRB's, with column
density consistent with that of Giant Molecular Clouds harbouring
star-formation in our Galaxy, as well as by evidences gathered in other
wavelengths. However, the volume density inferred by the fireball-jet model is
much lower than typical of a GMC, and I will confront this with the alternative
explanation of fireball expansion in a high dense medium, outlining the
problems that both models have at present. Finally I will briefly summarize
some results on dark GRB's, and describe the prospects of high resolution X-ray
spectroscopy in getting closer to the central environment of GRB, and far in
the Early Universe by using GRB as beacons to probe star and galaxy formation.Comment: 7 pages, 2 fig.s, invited talk at "GRB and Afterglow Astronomy 2001:
a workshop celebrating the first year of the HETE mission", Woods Hole, 5-9
Nov.200
Almacén de mercancías
Esta obra hace patente un problema con el que muy frecuentemente han de enfrentarse los arquitectos e ingenieros dotados de un especial instinto y deseo de creación, conscientes de la necesidad de añadir algo a la pura realización funcional de la construcción. Y no es más que el contraste que surge al tener que compaginarse dos elementos, inevitablemente algo distintos, como son las exigencias de la. obra en sí o de su dueño con la concepción del proyectista
Data-mining approach to investigate sedimentation features in combined sewer overflows
Sedimentation is the most common and effectively practiced method of urban drainage control in terms of operating installations and duration of service. Assessing the percentage of suspended solids removed after a given detention time is essential for both design and management purposes. In previous experimental studies by some of the authors, the expression of iso-removal curves (i.e. representing the water depth where a given percentage of suspended solids is removed after a given detention time in a sedimentation column) has been demonstrated to depend on two parameters which describe particle settling velocity and flocculation factor. This study proposes an investigation of the influence of some hydrological and pollutant aggregate information of the sampled events on both parameters. The Multi-Objective (EPR-MOGA) and Multi-Case Strategy (MCS-EPR) variants of the Evolutionary Polynomial Regression (EPR) are originally used as data-mining strategies. Results are proved to be consistent with previous findings in the field and some indications are drawn for relevant practical applicability and future studies
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