Neutrino cooled disk in post-merger system studied via numerical GR MHD simulation with a composition-dependent equation of state

The code HARM\_COOL, a conservative scheme for relativistic magnetohydrodynamics, is being developed in our group and works with a tabulated equation of state of dense matter. This EOS can be chosen and used during dynamical simulation, instead of the simple ideal gas one. In this case, the inversion scheme between the conserved and primitive variables is not a trivial task. In principle, the code needs to solve numerically five coupled non-linear equations at every time-step. The 5-D recovery schemes were originally implemented in HARM and worked accurately for a simple polytropic EOS which has an analytic form. Our current simulations support the composition-dependent EOS, formulated in terms of rest-mass density, temperature and electron fraction. In this proceeding, I discuss and compare several recovery schemes that have been included in our code. I also present and discuss their convergence tests. Finally, I show set of preliminary results of a numerical simulation, addressed to the post-merger system formed after the binary neutron stars (BNS) coalescence.Comment: 9 pages, 3 figures. To appear in the Proceedings of the 8th Conference of the Polish Society for Relativity, POTOR-8 (Warsaw, September 19-23, 2022

GLADIS: GLobal Accretion Disk Instability Simulation

I present the publicly available code GLADIS (GLobal Accretion Disk Instability Simulation) developed in my reserach group over the years 2002-2017. It can be freely downloaded and modified by the users via the link from the Astrophysics Source Code Library. The software computes time-dependent evolution of a black hole accretion disk, in one-dimensional, axisymmetric, vertically integrated scheme. The main applications are to explain the variability of accretion disks that can be subject to radiation-pressure instability. The phenomenon is relevant for fast variable microquasars, as well as for a class of changing-look AGN.Comment: 8 pages; submitted to the proceedings of Science; based on invited talk presented on the "Multifrequency Behaviour of High Energy Cosmic Sources - XIII", Palermo, June 3-8 201

Microphysics in GRB central engine

We study the structure and evolution of the accreting plasma in gamma ray burst central engines. The models are based on the general relativistic MHD simulations. The nuclear equation of state adequate for dense and degenerate plasma, is incorporated to the numerical scheme instead of a simple polytropic EOS. Plasma is cooled by neutrinos and energy is extracted from the rotating BH by magnetic fields. We discuss our results in the frame of the observable GRBs, and speculate about the origin of variability in the GRB jet emission. We also discuss the possible contribution from the heavy elements synthesized in winds from GRB engines to the kilonova emission.Comment: To be published in the proceedings of the XII Multifrequency Behaviour of High Energy Cosmic Sources Workshop, 12-17 June 2017, Palermo, Ital

Long Gamma Ray Bursts from binary black holes

We consider a scenario for the longest duration gamma ray bursts, resulting from the collapse of a massive rotating star in a close binary system with a companion black hole. The primary black hole born during the core collapse is first being spun up and increases its mass during the fallback of the stellar envelope just after its birth. As the companion black hole enters the outer envelope, it provides an additional angular momentum to the gas. After the infall and spiral-in towards the primary, the two black holes merge inside the circumbinary disk. The second episode of mass accretion and high final spin of the post-merger black hole prolongs the gamma ray burst central engine activity. The observed events should have two distinct peaks in the electromagnetic signal, separated by the gravitational wave emission. The gravitational recoil of the burst engine is also possible.Comment: 9 pages, 4 figures, accepted for publication in A&