A weakly magnetized (∼ 107G) neutron star, slowly spun up by accretion in an X-ray binary, crosses the instability boundary for r-mode instability at P=1–2 msec. The amplitude of the oscillation, which initially increases only at the spinup time scale, is secularly unstable due to the negative temperature dependence of the viscosity in neutron star matter, and diverges after a few hundred years...

We consider possible interpretations of the recently detected X-ray afterglow from the gamma-ray burst source GRB 970228. Cosmological and Galactic models of gamma-ray bursts predict different flux and spectral evolution of X-ray afterglows. We show that models based on adiabatic expansion of relativistic forward shocks require very efficient particle energization or post-burst re-acceleration ...

The degree and the temporal evolution of linear polarization in the prompt and afterglow emission of gamma-ray bursts is a very robust diagnostic of some key features of gamma-ray bursts jets and their micro and macro physics. In this contribution, I review the current status of the theory of polarized emission from GRB jets during the prompt, optical flash, and afterglow emission. I compare th...

Cosmic ray protons accelerated in the internal shocks of a long duration gamma ray burst can escape the fireball by converting to neutrons. Hadronic interactions of these neutrons inside a stellar wind bubble created by the progenitor star will produce TeV gamma rays via neutral meson decay and synchrotron radiation by charged pion-decay electrons in the wind magnetic field. Such gamma rays may...

GRB 990123 was the Ðrst burst from which simultaneous optical, X-ray, and gamma-ray emission was detected ; its afterglow has been followed by an extensive set of radio, optical, and X-ray observations. We have studied the gamma-ray burst itself as observed by the Compton Gamma Ray Observatory detectors. We Ðnd that gamma-ray Ñuxes are not correlated with the simultaneous optical observations a...

The origin of GRBs, bursts of 0.1 MeV—1 MeV photons lasting for a few seconds, remained unknown for over 20 years, primarily because GRBs were not detected prior to 1997 at wave-bands other than γ-rays [1]. The isotropic distribution of bursts over the sky suggested that GRB sources lie at cosmological distances, and general phenomenological considerations were used to argue that the bursts are...

Despite of more than 25 years of observational and theoretical investigations gamma{ray bursts are still an unresolved question. In this article we review the current status of observations of temporal and spectral properties of gamma{ray bursts and recent data on their spatial distribution. We discuss also the possible distance scales to gamma{ray bursts.