1,268 research outputs found
Population III Gamma Ray Bursts
We discuss a model of Poynting-dominated gamma-ray bursts from the collapse
of very massive first generation (pop. III) stars. From redshifts of order 20,
the resulting relativistic jets would radiate in the hard X-ray range around 50
keV and above, followed after roughly a day by an external shock component
peaking around a few keV. On the same timescales an inverse Compton component
around 75 GeV may be expected, as well as a possible infra-red flash. The
fluences of these components would be above the threshold for detectors such as
Swift and Fermi, providing potentially valuable information on the formation
and properties of what may be the first luminous objects and their black holes
in the high redshift Universe.Comment: 12 pages; Apj, subm. 12/10/2009; accepted 04/12/201
Gamma photometric redshifts for long gamma-ray bursts
It is known that the soft tail of the gamma-ray bursts' spectra show excesses
from the exact power-law dependence. In this article we show that this
departure can be detected in the peak flux ratios of different BATSE DISCSC
energy channels. This effect allows to estimate the redshift of the bright long
gamma-ray bursts in the BATSE Catalog. A verification of these redshifts is
obtained for the 8 GRB which have both BATSE DISCSC data and measured optical
spectroscopic redshifts. There is good correlation between the measured and
esti redshifts, and the average error is . The method is
similar to the photometric redshift estimation of galaxies in the optical
range, hence it can be called as "gamma photometric redshift estimation". The
estimated redshifts for the long bright gamma-ray bursts are up to . For the the faint long bursts - which should be up to - the
redshifts cannot be determined unambiguously with this method.Comment: accepted in A&A, 7 pages incl. 7 figure
Gamma Ray Bursts and Bursters
Major advances have been made in the field of gamma-ray bursts in the last
two years. The successful discovery of X-ray, optical and radio afterglows,
which were predicted by theory, 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. Current models envisage this 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. The substantial
agreement between observations and the theoretical predictions of the standard
fireball shock model provide confirmation of the basic aspects of this
scenario. The continued observations show a diversity of behavior, providing
valuable constraints for more detailed, post-standard models which incorporate
more realistic physical features. Crucial questions being now addressed are the
beaming at different energies and its implications for the energetics, 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: Invited talk at the 19th Texas Symposium on Relativistic Astrophysics
and Cosmology, Paris, Dec. 1998. To appear in Nuclear Phys. B, (Proceedings
Supplements), Elsevier Science; latex file, 15 pages, 6 figures, uses
espcrc2.sty, included; minor revision
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