Given the very accurate data from the BATSE and the Rossi X-Ray Timing Explorer and Chandra satellites, we use GRB 991216 as a prototypical case to test the theory that links the origin of the energy of gamma-ray bursts (GRBs) to the extractable energy of electromagnetic black holes (EMBHs). The fit of the afterglow fixes the only two free parameters of the model and leads to a new paradigm for the interpretation of the burst structure (the IBS paradigm). It leads as well to a reconsideration of the relative roles of the afterglow and burst in GRBs by defining two new phases in this complex phenomenon: (1) the injector phase, giving rise to the proper GRB, and (2) the beam-target phase, giving rise to the extended afterglow peak emission and to the afterglow. Such differentiation leads to a natural possible explanation of the bimodal distribution of GRBs observed by BATSE. The agreement with the observational data in regions extending from the horizon of the EMBH all the way out to the distant observer confirms the uniqueness of the model. Subject headings: black hole physics -gamma rays: bursts -supernovae: generalThe most decisive tool in the identification of the energetics of gamma-ray bursts (GRBs) has been the discovery by BeppoSAX of the afterglow phenomenon. In this Letter, we show how the afterglow data can be fitted using the theory that relates the GRB energy to the extraction process of the electromagnetic energy of a black hole endowed with electromagnetic structure (the EMBH model).

There is mounting evidence for the binary nature of the progenitors of gamma-ray bursts (GRBs). For a long GRB, the induced gravitational collapse (IGC) paradigm proposes as progenitor, or "in-state", a tight binary system composed of a carbon-oxygen core (CO core ) undergoing a supernova (SN) explosion which triggers hypercritical accretion onto a neutron star (NS) companion. For a short GRB, a NS-NS merger is traditionally adopted as the progenitor. We divide long and short GRBs into two sub-classes, depending on whether or not a black hole (BH) is formed in the merger or in the hypercritical accretion process exceeding the NS critical mass. For long bursts, when no BH is formed we have the sub-class of X-ray flashes (XRFs), with isotropic energy E iso 10 52 erg and rest-frame spectral peak energy E p,i 200 keV. When a BH is formed we have the sub-class of binary-driven hypernovae (BdHNe), with E iso 10 52 erg and E p,i 200 keV. In analogy, short bursts are similarly divided into two sub-classes. When no BH is formed, short gamma-ray flashes (S-GRFs) occur, with E iso 10 52 erg and E p,i 2 MeV. When a BH is formed, the authentic short GRBs (S-GRBs) occur, with E iso 10 52 erg and E p,i 2 MeV. We give examples and observational signatures of these four sub-classes and their rate of occurrence. From their respective rates it is possible that "in-states" of S-GRFs and S-GRBs originate from the "out-states" of XRFs. We indicate two additional progenitor systems: white dwarf-NS and BH-NS. These systems have hybrid features between long and short bursts. In the case of S-GRBs and BdHNe evidence is given of the coincidence of the onset of the high energy GeV emission with the birth of a Kerr BH.

The GRB 991216 and its relevant data acquired from the BATSE experiment and RXTE and Chandra satellites are used as a prototypical case to test the theory linking the origin of gamma ray bursts (GRBs) to the process of vacuum polarization occurring during the formation phase of a black hole endowed with electromagnetic structure (EMBH). The relative space-time transformation paradigm (RSTT paradigm) is presented. It relates the observed signals of GRBs to their past light cones, defining the events on the worldline of the source essential for the interpretation of the data. Since GRBs present regimes with unprecedently large Lorentz γ factor, also sharply varying with time, particular attention is given to the constitutive equations relating the four time variables: the comoving time, the laboratory time, the arrival time at the detector, duly corrected by the cosmological effects. This paradigm is at the very foundation of any possible interpretation of the data of GRBs.

Using GRB 991216 as a prototype, it is shown that the intensity substructures observed in what is generally called the "prompt emission" in gamma ray bursts (GRBs) do originate in the collision between the accelerated baryonic matter (ABM) pulse with inhomogeneities in the interstellar medium (ISM). The initial phase of such process occurs at a Lorentz factor γ ∼ 310. The crossing of ISM inhomogeneities of sizes ∆R ∼ 10 15 cm occurs in a detector arrival time interval of ∼ 0.4 s implying an apparent superluminal behavior of ∼ 10 5 c. The long lasting debate between the validity of the external shock model vs. the internal shock model for GRBs is solved in favor of the first.To reproduce the observed light curve of GRB 991216, we have adopted, as initial conditions (Ruffini et al. 2002a) at t = 10 −21 s ∼ 0 s, a spherical shell of electron-positronphoton neutral plasma laying between the radii r 0 = 6.03 × 10 6 cm and r 1 = 2.35 × 10 8 cm: the temperature of such a plasma is 2.2 MeV, the total energy E tot = 4.83 × 10 53 erg and the total number of pairs N e + e − = 1.99 × 10 58 .Such initial conditions follow from the EMBH theory we have recently developed based on energy extraction from a black hole endowed with electromagnetic structure (EMBH)

Following the induced gravitational collapse (IGC) paradigm of gamma-ray bursts (GRBs) associated with type Ib/c supernovae, we present numerical simulations of the explosion of a carbon-oxygen (CO) core in a binary system with a neutron-star (NS) companion. The supernova ejecta trigger a hypercritical accretion process onto the NS thanks to a copious neutrino emission and the trapping of photons within the accretion flow. We show that temperatures 1-10 MeV develop near the NS surface, hence electron-positron annihilation into neutrinos becomes the main cooling channel leading to accretion rates 10 −9 -10 −1 M s −1 and neutrino luminosities 10 43 -10 52 erg s −1 (the shorter the orbital period the higher the accretion rate). We estimate the maximum orbital period, P max , as a function of the NS initial mass, up to which the NS companion can reach by hypercritical accretion the critical mass for gravitational collapse leading to black-hole (BH) formation. We then estimate the effects of the accreting and orbiting NS companion onto a novel geometry of the supernova ejecta density profile. We present the results of a 1.4 × 10 7 particle simulation which show that the NS induces accentuated asymmetries in the ejecta density around the orbital plane. We elaborate on the observables associated with the above features of the IGC process. We apply this framework to specific GRBs: we find that X-ray flashes (XRFs) and binary-driven hypernovae (BdHNe) are produced in binaries with P > P max and P < P max , respectively. We analyze in detail the case of XRF 060218.

Context. The discovery by Swift and HETE-2 of an afterglow emission associated possibly with short GRBs opened the new problematic of their nature and classification. This issue has been further enhanced by the observation of GRB 060614 and by a new analysis of the BATSE catalog which led to the identification of a new class of GRBs with "an occasional softer extended emission lasting tenths of seconds after an initial spikelike emission". Aims. We plan a twofold task: a) to fit this new class of "hybrid" sources within our "canonical GRB" scenario, where all GRBs are generated by a "common engine" (i.e. the gravitational collapse to a black hole); b) to propose GRB 970228 as the prototype of the above mentioned class, since it shares the same morphology and observational features. Methods. We analyze BeppoSAX data on GRB 970228 within the "fireshell" model and we determine the parameters describing the source and the CircumBurst Medium (CBM) needed to reproduce its light curves in the 40-700 keV and 2-26 keV energy bands. Results. We find that GRB 970228 is a "canonical GRB", like e.g. GRB 050315, with the main peculiarity of a particularly low average density of the CBM n cbm ∼ 10 −3 particles/cm 3 . We also simulate the light curve corresponding to a rescaled CBM density profile with n cbm = 1 particle/cm 3 . From such a comparison it follows that the total time-integrated luminosity is a faithful indicator of the nature of GRBs, contrary to the peak luminosity which is merely a function of the CBM density. Conclusions. We call attention on discriminating the short GRBs between the "genuine" and the "fake" ones. The "genuine" ones are intrinsically short, with baryon loading B < ∼ 10 −5 , as stated in our original classification. The "fake" ones, characterized by an initial spikelike emission followed by an extended emission lasting tenths of seconds, have a baryon loading 10 −4 < ∼ B ≤ 10 −2 . They are observed as such only due to an underdense CBM consistent with a galactic halo environment which deflates the afterglow intensity.

A theoretical attempt to identify the physical process responsible for the afterglow emission of Gamma-Ray Bursts (GRBs) is presented, leading to the occurrence of thermal emission in the comoving frame of the shock wave giving rise to the bursts. The determination of the luminosities and spectra involves integration over an infinite number of Planckian spectra, weighted by appropriate relativistic transformations, each one corresponding to a different viewing angle in the past light cone of the observer. The relativistic transformations have been computed using the equations of motion of GRBs within our theory, giving special attention to the determination of the equitemporal surfaces. The only free parameter of the present theory is the "effective emitting area" in the shock wave front. A self consistent model for the observed hard-to-soft transition in GRBs is also presented. When applied to GRB 991216 a precise fit χ 2 ≃ 1.078 of the observed luminosity in the 2-10 keV band is obtained. Similarly, detailed estimates of the observed luminosity in the 50-300 keV and in the 10-50 keV bands are obtained.

We have performed our data analysis of the observations by Swift, NuStar and Fermi satellites in order to probe the induced gravitational collapse (IGC) paradigm for GRBs associated with supernovae (SNe), in the "terra incognita" of GRB 130427A. We compare and contrast our data analysis with those in the literature. We have verified that the GRB 130427A conforms to the IGC paradigm by examining the power law behavior of the luminosity in the early 10 4 s of the XRT observations. This has led to the identification of the four different episodes of the "binary driven hypernovae" (BdHNe) and to the prediction, on May 2, 2013, of the occurrence of SN 2013cq, duly observed in the optical band on May 13, 2013. The exceptional quality of the data has allowed the identification of novel features in Episode 3 including: a) the confirmation and the extension of the existence of the recently discovered "nested structure" in the late X-ray luminosity in GRB 130427A, as well as the identification of a spiky structure at 10 2 s in the cosmological rest-frame of the source; b) a power law emission of the GeV luminosity light curve and its onset at the end of Episode 2; c) different Lorentz Γ factors for the emitting regions of the X-ray and GeV emissions in this Episode 3. These results make it possible to test the details of the physical and astrophysical regimes at work in the BdHNe: 1) a newly born neutron star and the supernova ejecta, originating in Episode 1, 2) a newly formed black hole originating in Episode 2, and 3) the possible interaction among these components, observable in the standard features of Episode 3.