Long gamma-ray bursts as binary-driven hypernovae - analysis within the induced gravitational collapse paradigm

The central engine of long gamma-ray bursts (GRBs) is still under debate. The (currently) prevailing theoretical understanding is referred to as the standard fireball model. Here, the prompt emission is attributed to the internal shocks and the afterglow emission is attributed to the external shocks. The GRB outflow contains a wide range of bulk Lorentz factors. When a fast-moving portion overtakes the slower one, an internal shock is generated. On the other hand, the external shocks are caused by the interaction between the outflow and the circum-burst medium. However, data that was accumulated in the last 25 years challenges the overall picture. Some of the observed properties can not be explained within the standard framework. For example, the immense isotropic energy requirements of GRBs can be considerably reduced if one assumes the outflow is collimated. As a consequence, an achromatic break should appear in the afterglow light-curves. However, for the majority of GRBs the break is not achromatic, if present at all. In addition, the model itself does not deal with the exact mechanism of this initial energy release, but only its consequences. space{0.5cm} One of the alternatives to the fireball model is the fireshell model. Its origins can be traced back to the idea which revolves around the energy extraction from a charged black hole. During the years, with the implementation of new available data, the fireshell model evolved into the induced gravitational collapse (IGC) paradigm. This theory emphasizes the importance of binary system interaction for the GRB production mechanism, offering additional channels to study the role these systems have in GRB formation. In it, all GRBs originate from binary systems. Different observational properties are a direct consequence of a wide spectrum of acceptable binary system parameters. According to these observational properties, long and short GRBs are divided into nine different sub-classes. GRBs belonging to the type-I binary driven hypernova (BdHNe-I) class are of main interest in this thesis. The name is referring to GRBs with energies above $sim 10^{52}; m erg$ that originate from a collapse of a neutron star into a black hole. This collapse is initiated by the supernova explosion of its binary companion. space{0.5cm} In the work presented here, the theoretical framework of the IGC paradigm was tested on twelve GRBs. From these, only GRB 160829A is a member of the short GRB class. The remaining ones are long bursts, classified as BdHNe-I on the account of their energetics and GeV emission. Two main tools were put to use in order to analyze and interpret the data: the erb|rmfit| software and the simulation of the fireshell propagation that is available on our group's server. All of the GRBs were detected with the GBM detector onboard the extit{Fermi} satellite. Time-integrated and time-resolved analysis was carried out for each GRB in order to determine their isotropic equivalent energy and to possibly identify the P-GRB signature. The latter is expected to occur in the beginning of the prompt emission and to have a spectrum that shows a presence of thermal signatures. From 11 BdHNe-I, five had an identified P-GRB associated emission: GRB 100728A, GRB151027A, GRB 090618, GRB 110731A and GRB 141028A. A black body component was found in six GRBs. For three of them, the component did not exhibit the expected P-GRB spectral and temporal properties and it was therefore rejected as a possible P-GRB. GRB 110731A, GRB151027A and GRB 090618 were further interpreted within the fireshell model. Average values of circum-burst medium density inferred from the simulations are $sim0.03; m cm ^{-3}$, $sim15; m cm ^{-3}$ and $sim1; m cm ^{-3}$, respectively. Therefore, these bursts occurred in different environments. The averaged value of this sample, $sim$1 baryon per $; m cm ^{3}$, is consistent with previous findings. Baryon load and the relativistic Lorentz gamma factor at transparency point were also consistent with long GRBs, although we find that GRB 110731A shared some of these values with short bursts. In the case of short GRB 160829A, the fireshell simulation up to the transparency point was used in order to evaluate the redshift. Poor S/N ratio constrained its redshift to $z<5$. This is not particularly helpful considering it is true for all of the short GRBs observed so far. That is, if one does not take into account GRB 080913 at $z=6.7$, which was observed to last longer than $2; m s$ due to its high redshift, but it may be intrinsically short. The difficulties encountered during the analyses played a role in the further development of the IGC paradigm. The ongoing work is also discussed. It was devised with a goal to enable a more consistent and faster analysis. Then, a more complete BdHNe-I catalog with all of the fireshell parameters included would be easier to produce.