3,505 research outputs found
The Brightness Distribution of Bursting Sources in Relativistic Cosmologies
We present analytical solutions for the integral distribution of arbitrary
bursting or steady source counts as a function of peak photon count rate within
Friedmann cosmological models. We discuss both the standard candle and
truncated power-law luminosity function cases with a power-law density
evolution. While the analysis is quite general, the specific example discussed
here is that of a cosmological gamma-ray burst distribution. These solutions
show quantitatively the degree of dependence of the counts on the density and
luminosity function parameters, as well as the the weak dependence on the
closure parameter and the maximum redshift. An approximate comparison with the
publicly available Compton Gamma Ray Observatory data gives an estimate of the
maximum source luminosity and an upper limit to the minimum luminosity. We
discuss possible ways of further constraining the various parameters.Comment: 16 pages plus one figure, uuencoded postscript file. to appear in
Ap.J
Cosmological Brightness Distribution Fits of Gamma Ray Burst Sources
We discuss detailed fits of the BATSE and PVO gamma-ray burst peak-flux
distributions with Friedman models taking into account possible density
evolution and standard candle or power law luminosity functions. A chi-square
analysis is used to estimate the goodness of the fits and we derive the
significance level of limits on the density evolution and luminosity function
parameters. Cosmological models provide a good fit over a range of parameter
space which is physically reasonable.Comment: Ap.J. in press, uuencoded .ps file, 9 pages manuscript plus 5 figure
On Linkedness of Cartesian Product of Graphs
We study linkedness of Cartesian product of graphs and prove that the product
of an -linked and a -linked graphs is -linked if the graphs are
sufficiently large. Further bounds in terms of connectivity are shown. We
determine linkedness of product of paths and product of cycles
Origin of Gamma Ray Bursters
The successful discovery of X-ray, optical and radio afterglows of GRB has
made possible the identification of host galaxies at cosmological distances.
The energy release inferred in these outbursts place them among the most
energetic and violent events in the Universe. They are thought to be the
outcome of a cataclysmic stellar collapse or compact stellar merger, leading to
a relativistically expanding fireball, in which particles are accelerated at
shocks and produce nonthermal radiation. The substantial agreement between
observations and the theoretical predictions of the fireball shock model
provide confirmation of the basic aspects of this scenario. Among recent issues
are the collimation of the outflow and its implications for the energetics, the
production of prompt bright flashes at wavelenghts much longer than gamma-rays,
the time structure of the afterglow, its dependence on the central engine or
progenitor system behavior, and the role of the environment on the afterglow.Comment: Expanded version of a review to appear in Prog.Theor.Phys. S.136
(1999), "Black Holes and Gravitational Waves - New Eyes in the 21st Century",
Yukawa International Seminar'99, eds. T. Nakamura et al. Uses ptpsty.tex,
ptp-text.sty (included), 21 pages, 6 figure
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