GRB central engines and their electromagnetic transients

Massive hyper-accretion disks around black holes of mass ∼2−10M_⊙, with the accretion rate of about 0.01−10M_⊙s⁻¹, are considered to be plausible candidates for gamma-ray bursts’ central engine. Getting cool through neutrinos and anti-neutrinos efficiently, these accretion disks are called Neutrino Dominated Accretion Flows. Moreover, high magnetic field (∼ 10¹⁵⁻¹⁶G) and large density (∼ 10¹⁰g cm⁻³) can be considered as the two important physical features of Neutrino Dominated Accretion Flows, and as a result, self-gravity and gravitational instability might get highlighted in these dense accretion flows.

We have considered the effects of self-gravity together with those of magnetic field, on vertical structure of Neutrino Dominated Accretion Flows. The possibility of magnetic barrier and fragmentation processes, as the two promising mechanisms lead to late time X-ray flares, have studied as well.

On the other hand, as a consequence of gravitational instability, the outer disk’s fragmentation may result in a ring-like structure whose viscous evolution, at late times, can produce X-ray flares’ light curves. We also probe the possibility of such a mechanism as a responsible for flaring activity of GRB’s central engine.

Under the highly dense circumstances of the inner disk, Neutrino viscosity in addition to the impacts of self-gravity on the possibility of gravitational instability and fragmentation, in the inner zones, may result in a clumpy structure. The accretion of such a clumpy inner region of the disk can reproduce the highly variable light curve of the prompt emission. We investigate this scenario, as well.

To take the impacts of self-gravity in a General Relativistic Magneto-Hydro Dynamics (GRMHD) framework into consideration, we further computed the time-dependent axially-symmetric GRMHD model of a collapsar in the dynamical Kerr metric. Collapsing massive stars can account for Long Gamma Ray Bursts’ (GRBs) origines. We have explored the influence of self-gravity in such stars, where the newly formed black hole is of an increasing mass, and variable spin. We seek for the possibility of gravitational instability as well as self-gravity interfacial/ Rayleigh–Taylor instabilities. The effect of some magnetic field configurations on the outcome has been also studied.

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This is a hybrid event:
Room D, the Institute of Physics PAS, Al. Lotników 32/46

Online: https://meet.google.com/ccv-robc-rdn

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