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We present a model of a gamma-ray burst (GRB) related to “very massive” stars. In the framework of our model, the GRB phenomenon is a result of helium burning in degenerate conditions in a massive star (≳130  M ⊙ ), in which the thermal nuclear burning occurs in the deflagration regime and has a pulsating temporal pattern. The shock runs away from the burning (reaction) zone, which leads to the development of a coronal outflow (jet-like) structure. In our scenario the GRB observable prompt fast rise and decay part can be a result of photon propagation through the hot corona (Comptonization photosphere) of the star. On the other hand, the GRB afterglow is a cooling phase of the expanding and outflowing envelope. Presumably, the X-ray part of the GRB emergent spectrum is formed due to upscattering of soft photons of outer layers of the star off hot coronal electrons, and thus it should have a specific shape of the Comptonization spectrum.

The following sections are included: Introduction The overdensity computed with the UZC survey Results and conclusions Acknowledgments References

The study of propagation of Ultra High Energy Cosmic Rays (UHECR) is a key step in order to unveil the secret of their origin. Up to now it was considered only the influence of the galactic and the extragalactic magnetic fields. In this article we focus our analysis on the influence of the magnetic field of the galaxies standing between possible UHECR sources and us. Our main approach is to start from the well known galaxy distribution up to 120 Mpc. We use the most complete galaxy catalog: the LEDA catalog. Inside a sphere of 120 Mpc around us, we extract 60130 galaxies with known position. In our simulations we assign a Halo Dipole magnetic Field (HDF) to each galaxy. The code developed is able to retro-propagate a charged particle from the arrival points of UHECR data across our galaxies sample. We present simulations in case of Virgo cluster and show that there is a non negligible deviation in the case of protons of \\(7 \\times 10^{19}\\) eV, even if the \\(B\\) value is conservative. Then special attention is devoted to the AGASA triplet where we find that NGC3998 and NGC3992 could be possible candidates as sources.

Compton Gamma Ray Observatory, OSSE, SMM, TGRS, balloon and recent INTEGRAL data reveal a feature of the 0.511 MeV annihilation radiation of the Galactic Center with a flux of approximately 5x 10^{-4}~0.511 MeV photons cm^{-2} s^{-1}. We argue that e+e- pairs can be generated when the X-ray radiation photons and ~10-30 MeV photons interact with each other in the compact region in the proximity of the Galactic Center black hole. In fact, disks formed near black holes of 10^{17} g mass should emit the ~ 10 MeV temperature blackbody radiation. If positron e+ sources are producing about 10^{42} e+ s^{-1} near the Galactic Center they would annihilate on the way out and result in 0.511 MeV emission. We suggest that the annihilation radiation can be an observational consequence of the interaction of the accretion disk radiation of the SMall Mass Black Holes (SMMBHs) with X-ray radiation in the Galactic Center. This is probably the only way to identify and observe these SMMBHs.

We show how an emission endowed with an instantaneous thermal spectrum in the co-moving frame of the expanding fireshell can reproduce the time-integrated GRB observed non-thermal spectrum. An explicit example in the case of GRB 031203 is presented.

Within the \"fireshell\" model we define a \"canonical GRB\" light curve with two sharply different components: the Proper-GRB (P-GRB), emitted when the optically thick fireshell of electron-positron plasma originating the phenomenon reaches transparency, and the afterglow, emitted due to the collision between the remaining optically thin fireshell and the CircumBurst Medium (CBM). We here present the consequences of such a scenario on the theoretical interpretation of the nature of \"long\" and \"short\" GRBs.

(Shortened) [...] After recalling the basic features of the \"fireshell model\", we emphasize the following novel results: 1) the interpretation of the X-ray flares in GRB afterglows as due to the interaction of the optically thin fireshell with isolated clouds in the CircumBurst Medium (CBM); 2) an interpretation as \"fake - disguised\" short GRBs of the GRBs belonging to the class identified by Norris & Bonnell [...] consistent with an origin from the final coalescence of a binary system in the halo of their host galaxies with particularly low CBM density [...]; 3) the first attempt to study a genuine short GRB with the analysis of GRB 050509B, that reveals indeed still an open question; 4) the interpretation of the GRB-SN association in the case of GRB 060218 via the \"induced gravitational collapse\" process; 5) a first attempt to understand the nature of the \"Amati relation\", a phenomenological correlation between the isotropic-equivalent radiated energy of the prompt emission E_{iso} with the cosmological rest-frame \\nu F_{\\nu} spectrum peak energy E_{p,i}. In addition, recent progress on the thermalization of the electron-positron plasma close to their formation phase, as well as the structure of the electrodynamics of Kerr-Newman Black Holes are presented. An outlook for possible explanation of high-energy phenomena in GRBs to be expected from the AGILE and the Fermi satellites are discussed. As an example of high energy process, the work by Enrico Fermi dealing with ultrarelativistic collisions is examined. It is clear that all the GRB physics points to the existence of overcritical electrodynamical fields. In this sense we present some progresses on a unified approach to heavy nuclei and neutron stars cores, which leads to the existence of overcritical fields under the neutron star crust.