2 Search Results

In this paper we describe the afterglows of the long gamma-ray-burst (GRB) 130427A within the context of a binary-driven hypernova. The afterglows originate from the interaction between a newly born neutron star ($$ν$$NS), created by an Ic supernova (SN), and a mildly relativistic ejecta of a hypernova (HN). Such an HN in turn results from the impact of the GRB on the original SN Ic. The mildly relativistic expansion velocity of the afterglow ($Γ ~ 3$) is determined, using our model-independent approach, from the thermal emission between 196 and 461 s. The power law in the optical and X-ray bandsmore » of the afterglow is shown to arise from the synchrotron emission of relativistic electrons in the expanding magnetized HN ejecta. Two components contribute to the injected energy: the kinetic energy of the mildly relativistic expanding HN and the rotational energy of the fast-rotating highly magnetized $$ν$$NS. We reproduce the afterglow in all wavelengths from the optical (10¹⁴ Hz) to the X-ray band (10¹⁹ Hz) over times from 604 s to 5.18 × 10⁶ s relative to the Fermi-GBM trigger. Initially, the emission is dominated by the loss of kinetic energy of the HN component. After 10⁵ s the emission is dominated by the loss of rotational energy of the $$ν$$NS, for which we adopt an initial rotation period of 2 ms and a dipole plus quadrupole magnetic field of $$\lesssim$$ 7 × 10¹² G or ~10¹⁴ G. This scenario with a progenitor composed of a CO_core and an NS companion differs from the traditional ultra-relativistic-jetted treatments of the afterglows originating from a single black hole.« less

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 of 1–10 MeV develop near the NS surface, hence electron–positron annihilation into neutrinos becomes the main cooling channel leading to accretion rates of 10–9–$${10}^{-1}\,{M}_{\odot }$$ s–1 and neutrino luminosities of 10⁴³–10⁵² erg s^–1more » (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 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 $$1.4\times {10}^{7}$$ 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 are produced in binaries with $$P\gt {P}_{\max }$$ and $$P\lt {P}_{\max },$$ respectively. As a result, we analyze in detail the case of XRF 060218.« less