A simple physical model for long-duration gamma ray bursts (GRBs) is used to fit the redshift (z) and the jet opening-angle distributions measured with earlier GRB missions and with Swift. The effect of different sensitivities for GRB triggering is sufficient to explain the difference in the z distributions of the pre-Swift and Swift samples, with mean redshifts of 〈z〉 ∼= 1.5 and 〈z〉 ∼= 2.7, re...

Beginning with the γ-ray bursts GRB 970228 and GRB 970508, a standard model for the interpretation of GRB afterglows emerged involving synchrotron emission from a constant energy blast wave expanding into a constant density, “interstellar” medium. However, a massive star origin for GRBs implies a stellar wind environment, probably a Wolf-Rayet star, and we have previously suggested wind interac...

TeV or Super TeV neutrinos are expected to originate at the Gamma ray burster ( GRB ) events in the universe. These neutrinos are expected to be produced from the photo-meson interaction of the protons in the GRB environment. In the usual picture, the protons in the GRB fireball undergo Fermi acceleration in the ambient magnetic field of the GRB to very high energy. These protons then interact ...

Using a simple off-axis jet model of GRBs, we can reproduce the observed unusual properties of the prompt emission of GRB 980425, such as the extremely low isotropic equivalent γ-ray energy, the low peak energy, the high fluence ratio, and the long spectral lag when the jet with the standard energy of ∼ 10 ergs and the opening half-angle of 10 . ∆θ . 30 is seen from the off-axis viewing angle θ...

While the high-z frontier of star formation rate (SFR) studies has advanced rapidly, direct measurements beyond z ∼ 4 remain difficult, as shown by significant disagreements among different results. Gamma-ray bursts, owing to their brightness and association with massive stars, offer hope of clarifying this situation, provided that the GRB rate can be properly related to the SFR. The Swift GRB ...

GRB 970508 is the second gamma-ray burst (GRB) for which an optical afterglow has been detected. It is the first GRB for which a distance scale has been determined: absorption and emission features in spectra of the optical afterglow place GRB 970508 at a redshift of z ≥ 0.835 [1,2]. The lack of a Lyman-α forest in these spectra further constrains this redshift to be less than z ∼ 2.1. I show t...

The past year has witnessed a large increase in our knowledge of the polarization properties of Gamma-Ray Burst (GRB) radiation. In the prompt phase, the measurement (albeit highly debated) of a large degree of linear polarization in GRB 021206 has stimulated a deep theoretical study of polarization from GRB jets. The optical afterglow of GRB 030329, on the other hand, has been followed thoroug...

Context. Gamma-ray burst (GRB) emission is believed to originate in highly relativistic fireballs. Aims. Currently, only lower limits were securely set to the initial fireball Lorentz factor Γ0. We aim to provide a direct measure of Γ0. Methods. The early-time afterglow light curve carries information about Γ0, which determines the time of the afterglow peak. We have obtained early observations...

Gamma-ray burst (GRB) progenitors are observationally linked to the death of massive stars. X–ray studies of the GRB afterglows can deepen our knowledge of the ionization status and metal abundances of the matter in the GRB environment. Moreover, the presence of local matter can be inferred through its fingerprints in the X–ray spectrum, i.e. the presence of absorption higher than the Galactic ...

Radio observations of gamma-ray burst (GRB) afterglows are essential for our understanding of the physics of relativistic blast waves, as they enable us to follow the evolution of GRB explosions much longer than the afterglows in any other wave band. We have performed a 3-year monitoring campaign of GRB 030329 with the Westerbork Synthesis Radio Telescopes and the Giant Metrewave Radio Telescop...