Neutrino emission via proton-proton interaction and magnetic field screening in GRBs

Gamma-Ray Bursts (GRBs) are one of the most energetic astrophysical events of our Universe and a precise study of all the physical mechanisms occuring in these systems involves different branches of physics (from particles physics to General Relativity). The main subjects of this thesis concern the particles physics and the plasma physics fields. I study two different physical processes, operated by elementary particles as protons, electron/positron paris, photons and neutrinos, occuring in GRBs. In Ch. (1) I give a general introduction to GRBs, with some of their structural physical generalities and properties (as their different emission phases, spectral and temporal properties etc.). I introduce also the fireshell model, which has been developed during the years by Prof. Ruffini, R. and his group, in order to study and understand the several mechanisms behind the GRB emission. I will also highlight the principal differences between this model and the fireball model (which was the first model adopted in order to study the GRBs emission). The structure of the fireshell model considers a Reissner-Nordoström Black Hole, with a strong electric field that converts part of the BH total energy in e + e − plasma by the vacuum polarization process. These particles are accelerated and emit photons, and this leads to the formation of a relativistic optically thin fireshell of e + e − γ plasma (the “PEM–pulse”). This shell interacts with baryons, deposited in the ambient near the BH due to the collapse event, forming a new accelerated optically thick plasma of e + e − γ-baryons (PEMB–pulse). The transparency of this shell brings to the formation of the proper GRB emission (P-GRB emission). In Ch. (2) I introduce a classification of the GRBs in classes and subclasses. They differ from each other principally for their different progenitors, formation process, their isotropic energy E iso , their rest- frame spectral peak energy E p,i and local observed rate. In the Thesis, I have focused my attention principally on a particular type of long GRB class: the type I Binary-driven HyperNova (BdHN). The physical scenario and process, that leads to the formation of the BdHN class, is the Induced Gravitational Collapse (IGC), with the hypercritical accretion process paradigm. The two original studies of the Thesis, developed in Chs. (3) and (4), are based on the physical scenario of BdHN. In this chapter, I also show the connections between the several observations of a GRB event and the basic processes of the BdHN model. In Ch. (3), the first topic of the Thesis is presented, namely the neutrinos and photons production by proton-proton interaction, between accelerated protons and protons at rest. Keeping in mind the above discussed scenario for the dynamics of the e + e − γ-baryons plasma, recent numerical simulations have shown that the SN ejecta becomes highly asymmetric. Therefore, the electron-positron (e ± ) plasma created in the BH formation, during its isotropic and self-accelerating expansion, engulfs different amounts of ejecta baryons along different directions, leading to a direction-dependent Lorentz factor. In this configuration, I have studied the pp interaction occurring in two regions: an high density region and a low density region. In the conclusion of this chapter I also try to give an estimate of a possible, direct or indirect, detection of the neutrinos and photons created throught the above mechanism. From this analysis it came out that a possible detection of these neutrinos with currently operating detectors is plausible only for sources several order of magnitude more energetic than the ones considered in this work, and very-high energy ineracting protons (this subject is treated in App. (D) and will be better developed in future works). It also came out that an indirect detection of these neutrinos by means of the related photons emission is possible. The second subject of the Thesis is presented in Ch. (4) and concerns the study of the screening process of an electromagnetic field near a BH operated by electron-positron pairs. It has been shown that a rotating BH immersed in a test background magnetic field, of initial strength B 0 and aligned parallel to the BH rotation axis, generates an induced electric field, whose strength is proportional to the background magnetic field, E = 1/2 ΥB (where Υ is the BH spin parameter). In this analysis, I consider the configuration of crossed fields: B = Bẑ and E = E ŷ. In this system, an huge number of e + e − pairs can be emitted by vacuum polarization process, start to be accelerated to high energies by the induced electric field and emit synchrotron photons. These photons interact with the magnetic field via the magnetic pair production process (MPP): γ + B → e + + e − . The motion of all these particles around the magnetic field lines generates also an induced magnetic field oriented in the opposite direction to the background one, which implies a reduction of the background magnetic field. The principal results are that the combination of the processes described above can reduce the magnetic field in a small time scale, even if the production of pairs is not so efficient due to the low energy of the emitted photons, for the selected initial conditions of the field strengths and particles densities.