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Gamma-Ray Burst (GRB) explosions from the first generation of stars offer an exciting opportunity to probe the epoch of reionization. Clues about how and when the intergalactic medium was ionized can be read off their UV emission spectrum.…
Long gamma-ray bursts (GRBs) are commonly accepted to originate in the explosion of particularly massive stars, which gives rise to a highly relativistic jet. Internal inhomogeneities in the expanding flow give rise to internal shock waves…
The unrivalled, extreme luminosities of gamma-ray bursts (GRBs) make them the favored beacons for sampling the high redshift Universe. To employ GRBs to study the cosmic terrain -- e.g., star and galaxy formation history -- GRB luminosities…
The various possibilities for the progenitors of gamma-ray bursts (GRBs) manifest in differing observable properties. Through deep spectroscopic and high-resolution imaging observations of some GRB hosts, I demonstrate that well-localized…
Gamma-ray burst sources are distributed with a high level of isotropy, which is compatible with either a cosmological origin or an extended Galactic halo origin. The brightness distribution is another indicator used to characterize the…
Two classes of gamma-ray bursts have been identified in the BATSE catalogs characterized by durations shorter and longer than about 2 seconds. There are, however, some indications for the existence of a third one. Swift satellite detectors…
This article gives an overview of gamma-ray bursts (GRBs) and their relation to astroparticle physics and cosmology. GRBs are the most powerful explosions in the universe that occur roughly once per day and are characterized by flashes of…
The isotropic distribution of gamma-ray bursts as observed with the Burst and Transient Experiment (BATSE) strongly suggests that the bursts are at cosmological distances. At such distances, the expansion of the universe should redshift the…
Gamma-ray bursts (GRBs) are short, intense flashes of soft gamma-rays coming from the distant Universe. Long-duration GRBs (those lasting more than ~2 s) are believed to originate from the deaths of massive stars, mainly on the basis of a…
We examine the effects of time dilation on the temporal profiles of gamma-ray burst (GRB) pulses. By using prescriptions for the shape and evolution of prompt gamma-ray spectra, we can generate a simulated population of single pulsed GRBs…
The association of long gamma-ray bursts with supernovae naturally suggests that the cosmic GRB rate should trace the star formation history. Finding otherwise would provide important clues concerning these rare, curious phenomena. Using a…
We study the properties of short gamma-ray bursts (GRBs), based on the assumption that they are all connected to the binary neutron star mergers, whose formation mechanism contains a large amount of uncertainty. In particular, the merger…
Photoexcitation and ionization of partially ionized heavy atoms in highly relativistic flows by interstellar photons, followed by their reemission in radiative recombination and decay, boost star-light into beamed $\gamma$ rays along the…
Gamma ray bursts (GRBs) are known to come in two duration classes, separated at ~2 s. Long bursts originate from star forming regions in galaxies, have accompanying supernovae (SNe) when near enough to observe and are likely caused by…
The mechanism responsible for the prompt emission of gamma-ray bursts (GRBs) is still a debated issue. The prompt phase-related GRB correlations can allow to discriminate among the most plausible theoretical models explaining this emission.…
Cosmological gamma-ray bursts (GRBs) are probably powered by systems harboring a rotating black hole. These may result from hypernovae or black hole-neutron star coalescence. We identify short/long bursts with hyper- and suspended-accretion…
A review on the spectral and temporal properties of gamma-ray bursts is given. Special attention is paid to the spectral evolution of their continuum emission and its connection to the time evolution of the intensity. Efforts on…
The present common view about GRB origin is related to cosmology, what is based on statistical analysis, and on measurements of the redshifts in the GRB optical afterglows of long GRB. Models of radiation, and models of the central machine…
There is now an increasing number of evidence supporting the idea that the cosmic Gamma-ray Bursts (GRBs) originate from the collapse of massive stars in distant star-forming galaxies. Because GRBs are likely detectable up to very high…
The empirical classification of Gamma-Ray Bursts (GRBs) is based on their distribution in the plane of burst duration and spectral hardness. Two distinct distributions, long-soft and short-hard bursts, are observed in this plane, forming…