Microphysics in the Gamma-Ray Burst Central Engine

Abstract

We calculate the structure and evolution of a gamma ray burst central engine where an accreting torus has formed around the newly born black hole. We study the general relativistic, MHD models and we self-consistently incorporate the nuclear equation of state. The latter accounts for the degeneracy of relativistic electrons, protons, and neutrons, and is used in the dynamical simulation, instead of a standard polytropic γ-law. The EOS provides the conditions for the nuclear pressure in the function of density and temperature, which evolve with time according to the conservative MHD scheme. We analyze the structure of the torus and outflowing winds, and compute the neutrino flux emitted through the nuclear reactions balance in the dense and hot matter. We also estimate the rate of transfer of the black hole rotational energy to the bipolar jets. Finally, we elaborate on the nucleosynthesis of heavy elements in the accretion flow and the wind, through computations of the thermonuclear reaction network. We discuss the possible signatures of the radioactive elements decay in the accretion flow. We suggest that further detailed modeling of the accretion flow in GRB engine, together with its microphysics, may be a valuable tool to constrain the black hole mass and spin. It can be complementary to the gravitational wave analysis, if the waves are detected with an electromagnetic counterpart.

Shocks in the relativistic transonic accretion with low angular momentum

“…The simulations were performed on the Cray supercomupter cluster, typically using 16 nodes, and the message-passing interface supplemented with the hyperthreading technique was used, similarly as in Janiuk (2017). The code is supposed to conserve the axi-symmetry of the initial state, which we confirm.…”

“…We performed 1D to 3D hydrodynamical simulations of the non-magnetized accreting gas on the fixed background using the HARMPI 1 computational code (Ressler et al 2015(Ressler et al , 2017McKinney et al 2012;Tchekhovskoy et al 2007;Mignone & McKinney 2007;Janiuk et al 2013;Janiuk 2017) based on the original HARM code (Gammie et al 2003;McKinney & Gammie 2004). The background spacetime is given by the stationary Kerr solution.…”

Study of Timing Evolution from Nonvariable to Structured Large-amplitude Variability Transition in GRS 1915 + 105 Using AstroSat

“…The large-amplitude variability κ and λ classes are not observed as often (Belloni et al 1997a,b). The origin of such large amplitude variability is usually associated with the radiationpressure instability due to its persistently high, near-Eddington mass accretion rate (Janiuk et al 2000). In another approach, Nayakshin et al (2001) showed that a modified viscosity law could reproduce large-amplitude variability qualitatively.…”

Accretion in a Dynamical Spacetime and the Spinning Up of the Black Hole in the Gamma-Ray Burst Central Engine

“…The hole itself should also fastly rotate, in order to efficiently transport the power to the remote jets. Both Blandford-Znajek process and neutrino anihillation may act as the source of this power, and in these two mechanisms their efficiency is similarly scaled with the agnes@cft.edu.pl arXiv:1810.05261v1 [astro-ph.HE] 11 Oct 2018 black hole spin Liu et al 2015;Janiuk 2017). The process is further mitigated by the magnetic fields.…”