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Author: Publisher: ISBN: Category : Languages : en Pages :
Book Description
Spectral measurements by the Solar Maximum Mission have been used to confirm the cyclotron lines in gamma-ray bursts reported from the Konus experiment. We present ISEE-3 data for the same burst (GB800419) during the same period of time which show no line. We discuss various problems in the analysis of scintillator spectra and point out that unfolded spectra are not necessarily unique and that the position of a data point in a deconvolved spectrum may vary depending on the assumed overall shape of the spectrum. As a result, if the analysis assumes a soft spectrum (such as optically thin thermal bremsstrahlung) an absorption feature might appear, whereas a harder spectrum (such as a Comptonized blackbody) would not require the feature. Since the continuum shape probably changes during the duration of a typical burst, the nonuniqueness of the spectral unfolding, combined with the assumption that the continuum is optically thin thermal bremsstrahlung, could give rise to spurious absorption features which vary on a time scale of seconds. Despite these problems, there is still some evidence for narrow spectral lines in the range 45 to 65 keV but not for the broad lines reported from the Konus experiment. Unfortunately, the range 45 to 65 keV is the most difficult spectral region to unfold.
Author: Publisher: ISBN: Category : Languages : en Pages :
Book Description
Spectral measurements by the Solar Maximum Mission have been used to confirm the cyclotron lines in gamma-ray bursts reported from the Konus experiment. We present ISEE-3 data for the same burst (GB800419) during the same period of time which show no line. We discuss various problems in the analysis of scintillator spectra and point out that unfolded spectra are not necessarily unique and that the position of a data point in a deconvolved spectrum may vary depending on the assumed overall shape of the spectrum. As a result, if the analysis assumes a soft spectrum (such as optically thin thermal bremsstrahlung) an absorption feature might appear, whereas a harder spectrum (such as a Comptonized blackbody) would not require the feature. Since the continuum shape probably changes during the duration of a typical burst, the nonuniqueness of the spectral unfolding, combined with the assumption that the continuum is optically thin thermal bremsstrahlung, could give rise to spurious absorption features which vary on a time scale of seconds. Despite these problems, there is still some evidence for narrow spectral lines in the range 45 to 65 keV but not for the broad lines reported from the Konus experiment. Unfortunately, the range 45 to 65 keV is the most difficult spectral region to unfold.
Author: Publisher: ISBN: Category : Languages : en Pages : 3
Book Description
This report summarizes the work carried out under LLNL Contract Number B108527, subcontracted by the Regents of the University of California at Berkeley. The research carried out under this contract includes assisting in the data analysis for the Prognoz-9 mission, linking results of the computer codes to the Prognoz-9 data library in order to study the spectral shape and evolution of cosmic gamma-ray burst energy spectra, and using the results of this study to help to determine or constrain the physical conditions at the gamma-ray bursts sources. The results of this work led to several publications that have shed considerable insight into the gamma-ray burst mystery, and gives a new diagnostic for determining the nature of gamma-ray burst sources. The outcome of this work also provides a new spectral form for studying the temporal evolution and spectral behavior of gamma-ray bursts.
Author: Gordon Gilmore Publisher: John Wiley & Sons ISBN: 1119964695 Category : Science Languages : en Pages : 597
Book Description
The Second Edition of Practical Gamma-Ray Spectrometry has been completely revised and updated, providing comprehensive coverage of the whole gamma-ray detection and spectrum analysis processes. Drawn on many years of teaching experience to produce this uniquely practical volume, issues discussed include the origin of gamma-rays and the issue of quality assurance in gamma-ray spectrometry. This new edition also covers the analysis of decommissioned nuclear plants, computer modelling systems for calibration, uncertainty measurements in QA, and many more topics.
Author: Gilbert Vedrenne Publisher: Springer Science & Business Media ISBN: 354039088X Category : Science Languages : en Pages : 613
Book Description
Since their discovery was first announced in 1973, gamma-ray bursts (GRBs) have been among the most fascination objects in the universe. While the initial mystery has gone, the fascination continues, sustained by the close connection linking GRBs with some of the most fundamental topics in modern astrophysics and cosmology. Both authors have been active in GRB observations for over two decades and have produced an outstanding account on both the history and the perspectives of GRB research.
Author: Cheng Ho Publisher: Cambridge University Press ISBN: 9780521414494 Category : Nature Languages : en Pages : 532
Book Description
Summarizes the current understanding of Astronomical gamma-ray bursts, short-lived flashes of high-energy radiation, which have eluded even a basic explanation for over twenty years, and describes directions for future research.
Author: Alexander Lazarian Publisher: Springer ISBN: 3662446251 Category : Science Languages : en Pages : 627
Book Description
This volume presents the current knowledge of magnetic fields in diffuse astrophysical media. Starting with an overview of 21st century instrumentation to observe astrophysical magnetic fields, the chapters cover observational techniques, origin of magnetic fields, magnetic turbulence, basic processes in magnetized fluids, the role of magnetic fields for cosmic rays, in the interstellar medium and for star formation. Written by a group of leading experts the book represents an excellent overview of the field. Nonspecialists will find sufficient background to enter the field and be able to appreciate the state of the art.
Author: James C. Bezdek Publisher: Springer Science & Business Media ISBN: 147570450X Category : Mathematics Languages : en Pages : 267
Book Description
The fuzzy set was conceived as a result of an attempt to come to grips with the problem of pattern recognition in the context of imprecisely defined categories. In such cases, the belonging of an object to a class is a matter of degree, as is the question of whether or not a group of objects form a cluster. A pioneering application of the theory of fuzzy sets to cluster analysis was made in 1969 by Ruspini. It was not until 1973, however, when the appearance of the work by Dunn and Bezdek on the Fuzzy ISODATA (or fuzzy c-means) algorithms became a landmark in the theory of cluster analysis, that the relevance of the theory of fuzzy sets to cluster analysis and pattern recognition became clearly established. Since then, the theory of fuzzy clustering has developed rapidly and fruitfully, with the author of the present monograph contributing a major share of what we know today. In their seminal work, Bezdek and Dunn have introduced the basic idea of determining the fuzzy clusters by minimizing an appropriately defined functional, and have derived iterative algorithms for computing the membership functions for the clusters in question. The important issue of convergence of such algorithms has become much better understood as a result of recent work which is described in the monograph.
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Author: Jay Preston Norris
Author: Bing Zhang
Author: Gordon Gilmore
Author: Gilbert Vedrenne
Author: Cheng Ho
Author: Alexander Lazarian
Author: Timothy W. Giblin
Author: James C. Bezdek