The vast majority of the celestial gamma-ray sources detected so far have not yet been identified with secure counterparts at other wavelenghts. Here we report the preliminary evidence of a probable association between galaxy clusters and unidentified gamma-ray sources of high galactic latitude (|b| > 20 deg) in the Third EGRET catalog. All of the clusters which are most probably associated wit...

We present a study of the unidentified gamma-ray source 3EG J0542+2610. This source is spatially superposed to the supernova remnant G180.0-1.7, but its time variability makes unlikely a physical link. We have searched into the EGRET location error box for compact radio sources that could be the low energy counterpart of the gamma-ray source. Although 29 point-like radio sources were detected a...

It is widely believed that outflows of gamma-ray bursts are jetted. Some people also suggest that the jets may have structures like ǫ(θ) ∝ θ. We test the possibility of X-ray flashes coming from such jets in this paper. Both qualitative and quantitative analyses have shown that this model can reproduce most observational features for both X-ray flashes and gamma-ray bursts. Using common paramet...

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...