240 research outputs found

    X-Ray Afterglows of Gamma-Ray Bursts

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    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 >10deg‚Ā°>10 \deg.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

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    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

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    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

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    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

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    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

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    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 creaci√≥n, conscientes de la necesidad de a√Īadir algo a la pura realizaci√≥n funcional de la construcci√≥n. Y no es m√°s que el contraste que surge al tener que compaginarse dos elementos, inevitablemente algo distintos, como son las exigencias de la. obra en s√≠ o de su due√Īo con la concepci√≥n del proyectista
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