Data: 21.10.2025

Gerardo Urrutia Sanchez (CFT,PL)

Numerical simulations of jet launching and breakout from collapsars

Streszczenie:
Long Gamma-Ray Bursts (LGRBs) are associated with the collapse of massive stars. The gamma radiation lasts between two and hundreds of seconds and luminosities of $L_j\sim 10^{53},$erg,s$^{-1}$. The subsequent afterglow lasts from days to several months in a wide range of frequencies, from X-rays to radio. The mechanism producing LGRB jets and failed jets remains uncertain due to the complex collapse. In addition, failed jets may lead to different types of transients. Simulating the entire GRB dynamics from its production until the jet's breakout from the stellar envelope is computationally expensive. Most of the studies on jet dynamics are limited to intermediate scales, lossing self-consistency with the accretion process. In this work, we investigate jet production at the black hole horizon and its evolution beyond the envelope boundary. We perform 2.5-dimensional GRMHD simulations. For the initial conditions, we use remapped massive star progenitors that have been previously evolved with a state-of-the-art stellar evolutionary code. Specifically, we adopt the Wolf-Rayet star models 12TH and 16TI from the Woosley & Heger framework, and we evolve our own Long GRB progenitor with the MESA code. A dipolar magnetic field is imposed, with variations in field strength to explore its influence. Our simulations show that a collapsar launches a successful, relativistic jet only when a strong, large-scale dipolar field is present, driving a magnetically arrested disk. The resulting jets have luminosities of $L_{j}\sim10^{49}$--$10^{53},$erg,s$^{-1}$. The final energy structure, collimation, and breakout time reveal that magnetisation distribution and progenitor stratification are the key determinants of jet structure and success.