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.

We here propose a new model-independent technique to overcome the circularity problem affecting the use of gamma-ray bursts (GRBs) as distance indicators through the use of Ep−Eiso correlation. We calibrate the Ep−Eiso correlation and find the GRB distance moduli that can be used to constrain dark energy models. We use observational Hubble data to approximate the cosmic evolution through Bézier parametric curve obtained through the linear combination of Bernstein basis polynomials. In doing so, we build up a new data set consisting of 193 GRB distance moduli. We combine this sample with the supernova JLA data set to test the standard ΛCDM model and its wCDM extension. We place observational constraints on the cosmological parameters through Markov Chain Monte Carlo numerical technique. Moreover, we compare the theoretical scenarios by performing the Akaike and Deviance Information statistical criteria.the 2σ level, while for the wCDM model we obtain $\Omega _m=0.34^{+0.13}_{-0.15}$ and $w=-0.86^{+0.36}_{-0.38}$ at the 2σ level. Our analysis suggests that ΛCDM model is statistically favoured over the wCDM scenario. No evidence for extension of the ΛCDM model is found.

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.

We analyze the early X-ray flares in the GRB "flare-plateau-afterglow" (FPA) phase observed by Swift-XRT. The FPA occurs only in one of the seven GRB subclasses: the binary-driven hypernovae (BdHNe). This subclass consists of long GRBs with a carbon-oxygen core and a neutron star (NS) binary companion as progenitors. The hypercritical accretion of the supernova (SN) ejecta onto the NS can lead to the gravitational collapse of the NS into a black hole. Consequently, one can observe a GRB emission with isotropic energy E iso 10 52 erg, as well as the associated GeV emission and the FPA phase. Previous work had shown that gamma-ray spikes in the prompt emission occur at ∼ 10 15 -10 17 cm with Lorentz gamma factor Γ ∼ 10 2 -10 3 . Using a novel data analysis we show that the time of occurrence, duration, luminosity and total energy of the X-ray flares correlate with E iso . A crucial feature is the observation of thermal emission in the X-ray flares that we show occurs at radii ∼ 10 12 cm with Γ 4. These model independent observations cannot be explained by the "fireball" model, which postulates synchrotron and inverse Compton radiation from a single ultra relativistic jetted emission extending from the prompt to the late afterglow and GeV emission phases. We show that in BdHNe a collision between the GRB and the SN ejecta occurs at 10 10 cm reaching transparency at ∼ 10 12 cm with Γ 4. The agreement between the thermal emission observations and these theoretically derived values validates our model and opens the possibility of testing each BdHN episode with the corresponding Lorentz gamma factor.

Context. Data from cosmic microwave background radiation (CMB), baryon acoustic oscillations (BAO), and supernovae Ia (SNe-Ia) support a constant dark energy equation of state with w 0 ∼ −1. Measuring the evolution of w along the redshift is one of the most demanding challenges for observational cosmology. Aims. We discuss the existence of a close relation for gamma-ray bursts (GRBs), named Combo-relation, based on characteristic parameters of GRB phenomenology such as the prompt intrinsic peak energy E p,i , the X-ray afterglow initial luminosity L 0 and the rest-frame duration τ of the shallow phase, and the index of the late power-law decay α X . We use it to measure Ω m and the evolution of the dark energy equation of state. We also propose a new calibration method for the same relation, which reduces the dependence on SNe Ia systematics. Methods. We have selected a sample of GRBs with 1) a measured redshift z; 2) a determined intrinsic prompt peak energy E p,i ; and 3) a good coverage of the observed (0.3-10) keV afterglow light curves. The fitting technique of the rest-frame (0.3-10) keV luminosity light curves represents the core of the Combo-relation. We separate the early steep decay, considered a part of the prompt emission, from the X-ray afterglow additional component. Data with the largest positive residual, identified as flares, are automatically eliminated until the p-value of the fit becomes greater than 0.3. Results. We strongly minimize the dependency of the Combo-GRB calibration on SNe Ia. We also measure a small extra-Poissonian scatter of the Combo-relation, which allows us to infer from GRBs alone Ω M = 0.29 Conclusions. In view of the increasing size of the GRB database, thanks to future missions, the Combo-relation is a promising tool for measuring Ω m with an accuracy comparable to that exhibited by SNe Ia, and to investigate the dark energy contribution and evolution up to z ∼ 10.

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Context. It has been recently shown that GRB 090618, observed by AGILE, Coronas Photon, Fermi, Konus, Suzaku, and Swift, is composed of two very different components: episode 1, lasting 50 s, shows a thermal plus power-law spectrum with a characteristic temperature evolving in time as a power law; episode 2 (the remaining 100 s) is a canonical long GRB. We have associated episode 1 to the progenitor of a collapsing bare core leading to the formation of a black hole: what was defined as a "proto black hole" Aims. In precise analogy with GRB 090618 we aim to analyze the 89 s of the emission of GRB 101023, observed by Fermi, Gemini, Konus and Swift, to see if there are two different episodes: the first one presenting a characteristic black-body temperature evolving in time as a broken power law, and the second one consistent with a canonical GRB. Methods. To obtain information on the spectra, we analyzed the data provided by the GBM detector onboard the Fermi satellite, and we used the heasoft package XSPEC and RMFIT to obtain their spectral distribution. We also used the numerical code GRBsim to simulate the emission in the context of the fireshell scenario for episode 2. Results. We confirm that the first episode can be well fit by a black body plus power-law spectral model. The temperature changes with time following a broken power law, and the photon index of the power-law component presents a soft-to-hard evolution. We estimate that the radius of this source increases with time with a velocity of 1.5 × 10 4 km s −1 . The second episode appears to be a canonical GRB. By using the Amati and the Atteia relations, we determined the cosmological redshift, z ∼ 0.9±0.084(stat.)±0.2(sys.). The results of GRB 090618 are compared and contrasted with the results of GRB 101023. Particularly striking is the scaling law of the soft X-ray component of the afterglow. Conclusions. We identify GRB 090618 and GRB 101023 with a new family of GRBs related to a single core collapse and presenting two astrophysical components: a first one related to the proto-black hole prior to the process of gravitational collapse (episode 1), and a second one, which is the canonical GRB (episode 2) emitted during the formation of the black hole. For the first time we are witnessing the process of a black hole formation from the instants preceding the gravitational collapse up to the GRB emission. This analysis indicates progress towards developing a GRB distance indicator based on understanding the P-GRB and the prompt emission, as well as the soft X-ray behavior of the late afterglow.

The time-resolved spectral analysis of GRB 090227B, made possible by the Fermi-GBM data, allows us to identify in this source the missing link between the genuine short and long gamma-ray bursts (GRBs). Within the Fireshell model of the GRBs we predict genuine short GRBs: bursts with the same inner engine of the long bursts but endowed with a severely low value of the baryon load, B 5 × 10 −5 . A first energetically predominant emission occurs at the transparency of the e + e − plasma, the Proper-GRB (P-GRB), followed by a softer emission, the extended afterglow. The typical separation between the two emissions is expected to be of the order of 10 −3 -10 −2 s. We identify the P-GRB of GRB 090227B in the first 96 ms of emission, where a thermal component with the temperature kT = (517 ± 28) keV and a flux comparable with the non-thermal part of the spectrum is observed. This non-thermal component as well as the subsequent emission, where there is no evidence for a thermal spectrum, is identified with the extended afterglow. We deduce a theoretical cosmological redshift z = 1.61 ± 0.14. We then derive the total energy E tot e + e − = (2.83 ± 0.15) × 10 53 erg, the baryon load B = (4.13 ± 0.05) × 10 −5 , the Lorentz Γ factor at transparency Γ tr = (1.44 ± 0.01) × 10 4 , and the intrinsic duration Δt ∼ 0.35 s. We also determine the average density of the circumburst medium (CBM), n CBM = (1.90 ± 0.20) × 10 −5 particles cm −3 . There is no evidence of beaming in the system. In view of the energetics and of the baryon load of the source, as well as of the low interstellar medium and of the intrinsic timescale of the signal, we identify the GRB progenitor as a binary neutron star. From the recent progress in the theory of neutron stars, we obtain masses of the stars m 1 = m 2 = 1.34 M and their corresponding radii R 1 = R 2 = 12.24 km and thickness of their crusts ∼0.47 km, consistent with the above values of the baryon load, of the energetics and of the time duration of the event.