Nucleosynthesis of elements in gamma-ray burst engines

Abstract

Aims. We consider the gamma-ray burst (GRB) central engine that is powered by the collapse of a massive rotating star or compact binary merger. The engine is a hot and dense accretion disk, which is composed of free nucleons, electron-positron pairs, and helium, and cooled by neutrino emission. A significant number density of neutrons in the inner disk body provide conditions for neutron rich plasma in the GRB outflows or jets. helium is synthesized in the inner disk if the accretion rate is large, and heavy nuclei are also formed in the outer disk at distances above 150−250r g from the black hole. We study the process of nucleosynthesis in the GRB engine, depending on its physical properties. Methods. The GRB central engine is hydrodynamically modelled in the frame of a dense and hot disk, which accretes with a high rate (up to 1 Solar mass per second) onto a maximally spinning, stellar mass black hole. The synthesis of heavy nuclei up to germanium and gallium is then followed by the nuclear reaction network. Results. The accretion at high rate onto a Kerr black hole feeds the engine activity and establishes conditions for efficient synthesis of heavy nuclei in the disk. These processes may have important observational implications for the jet deceleration process and heavy elements observed in the spectra of GRB afterglows.

Microphysics in the Gamma-Ray Burst Central Engine

“…We use here a standard, publicly available software, and a more detailed description of our procedure can be found in Janiuk (2014). In Figure 10 we plot the electron fraction in the 2-D maps of the accretion flow.…”

“…In the outer parts of the disc, the heavy elements can be formed, and then the isotopes are prone to the radioactive decay (Fujimoto et al 2004). This may in the future bring observable effects on the measured hard Xray spectra of GRBs (Janiuk 2014) as well as the additional peaks in the blue and infrared bands a few days after the prompt GRB emission (Martin et al 2015). In addition, the gamma ray bursts contribute in this way to the galactic chemical evolution (Surman et al 2014).…”

Black Hole Accretion in Gamma Ray Bursts

“…For the NuSTAR satellite, sensitive in the 5-80 keV range, it's in principle possible to detect the photons from Ti, Co, Mn, Cu, Zn, Ga, Cr unstable isotopes decays. Additionally, the EPIC detector onboard the XMM-Newton, could be able to see lines below 15 keV, e.g., 45 Ti, 57 Mn, or 57 Co [26]. In Figure 3, we plot an example result of the nucleosynthesis computations, showing the volume integrated abundance distribution of elements, in the function of their mass number.…”

Nucleosynthesis in Supernovae, Hypernovae/Gamma-ray Bursts and Compact Binary Mergers

“…For the role of weak interactions and resulting nucleosynthesis see e.g. [25,69,70]). The basic (consensus) picture is the following: explosion energies can be found up to 5 × 10 52 erg, 56 Ni ejecta up to 0.5 M ⊙ , and the ejecta are beamed with relativistic jets.…”