1,290 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
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
The Fireball Shock Model of Gamma Ray Bursts
Gamma-ray bursts are thought to be the outcome of a cataclysmic event leading
to a relativistically expanding fireball, in which particles are accelerated at
shocks and produce nonthermal radiation. We discuss the theoretical predictions
of the fireball shock model and its general agreement with observations. Some
of the recent work deals with the collimation of the outflow and its
implications for the energe tics, 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 evolution of the afterglow.Comment: To appear in "Cosmic Explosions", Procs. 10th October Astrophysics
Conference, Maryland, Oct. 11-13 1999; 13 pages, 3 figures, aipproc.st
Gamma Ray Burst Afterglows and their Implications
The discovery of X-ray, optical and radio afterglows of GRBs provides an
important tool for understanding these sources. Most current models envisage
GRB as arising in a cataclysmic stellar event leading to a relativistically
expanding fireball, where particle acceleration at shocks lead to nonthermal
radiation. The predictions of this scenario are in substantial agreement with
the bulk of the observations. In addition, the data show a diversity of finer
structure behavior, which is providing constraints for more detailed models.
Current issues of interest are the implications of the beaming for the
energetics, the afterglow time structure, dependence on progenitor system, and
the role of the environment.Comment: Invited talk at the Rome Conference on Gamma Ray Bursts in the
Afterglow Age; latex file, 4 pages, 4 figures, uses aa macro
Theories of GRB Early Afterglow
The rapid follow-up of gamma-ray burst (GRB) afterglows made possible by the
multi-wavelength satellite Swift, launched in November 2004, has put under a
microscope the GRB early post-burst behavior, This is leading to a significant
reappraisal and expansion of the standard view of the GRB early afterglow
behavior, and its connection to the prompt gamma-ray emission. In addition to
opening up the previously poorly known behavior on minutes to hours timescales,
two other new pieces in the GRB puzzle being filled in are the the discovery
and follow-up of short GRB afterglows, and the opening up of the z\simg 6
redshift range. We review some of the current theoretical interpretations of
these new phenomena.Comment: 10 pages, 1 figure, uses aipproc.cls; to appear in ``16th Annual
October Astrophysics Conference in Maryland", eds. S. Holt, N. Gehrels and J.
Nousek, AIP Conf.Proc
Some observational tests of X-ray pulsar emission models
The understanding of neutron star physics which relies heavily on knowing values of their mass, radius and magnetic field strength was studied. The only information about these till now comes from the surface radiation. Major uncertainties concerning the nature of the mass exchange and the accretion flow, the magnetopause structure, the infall deceleration, the actual pulsation mechanism and the atmosphere geometry are examined. The alternatives and several possible observational tests are discussed
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