On the Role of a Cavity in the Hypernova Ejecta of GRB 190114C

Abstract

Within the binary-driven hypernova I (BdHN I) scenario, the gamma-ray burst GRB190114C originates in a binary system composed of a massive carbon-oxygen core (CO core ), and a binary neutron star (NS) companion. As the CO core undergoes a supernova explosion with the creation of a new neutron star (νNS), hypercritical accretion occurs onto the companion binary neutron star until it exceeds the critical mass for gravitational collapse. The formation of a black hole (BH) captures 10 57 baryons by enclosing them within its horizon, and thus a cavity of approximately 10 11 cm is formed around it with initial density 10 −7 g/cm 3 . A further depletion of baryons in the cavity originates from the expansion of the electron-positron-photon (e + e − γ) plasma formed at the collapse, reaching a density of 10 −14 g/cm 3 by the end of the interaction. It is demonstrated here using an analytical model complemented by a hydrodynamical numerical simulation that part of the e + e − γ plasma is reflected off the walls of the cavity. The consequent outflow and its observed properties are shown to coincide with the featureless emission occurring in a time interval of duration t rf , measured in the rest frame of the source, between 11 and 20 s of the GBM observation. Moreover, similar features of the GRB light curve were previously observed in GRB 090926A and GRB 130427A, all belonging to the BdHN I class. This interpretation supports the general conceptual framework presented in ) and guarantees that a low baryon density is reached in the cavity, a necessary condition for the operation of the "inner engine" of the GRB presented in an accompanying article (Ruffini & Moradi 2019).

Induced Gravitational Collapse, Binary-Driven Hypernovae, Long Gramma-ray Bursts and Their Connection with Short Gamma-ray Bursts

“…We have taken the opportunity to include a brief summary of very recent developments published during the peer-review process of this article. These results cover the explanation of the observed GeV emission in BdHNe [84][85][86][87]. One of the most relevant aspects of this topic is that it requests the solution of one of the fundamental problems in relativistic astrophysics: how to extract the rotational energy from a BH.…”

“…In the case of BH formation, the rotation of the BH together with the presence of the magnetic field inherited from the NS and the surrounding matter conform to what we have called the inner engine of the high-energy emission [84][85][86][87]. The electromagnetic field of the engine is mathematically described by the Wald solution [88].…”

“…The asymmetric ejecta includes a "cavity" of ∼10 11 cm of very low-density matter around the newborn BH. The hydrodynamics inside such a low-density cavity have been recently studied by numerical simulations in [87].…”

“…The newborn Kerr BH, surrounded by ejecta and immersed in a test magnetic field (likely the one left by the magnetized, collapsed NS), represents what we have called the inner engine of the high-energy emission [84][85][86][87]. The rotating BH, of mass M and angular momentum J, in the presence of the magnetic field B 0 , induces an electromagnetic field described by the Wald solution [88].…”

“…In the direction pointing from the CO core to the accreting NS outwards and lying on the orbital plane, the aforementioned cavity represents a region of low baryonic contamination [86,87]. The e + e− plasma can then self-accelerate to Lorentz factors Γ ∼ 10 2 -10 3 reaching transparency and impacting on the CBM filaments as described in [37,110,111].…”