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The propagation of long GRB jets through and beyond its progenitor star

Gerardo Urrutia, Agnieszka Janiuk

TL;DR

The paper investigates how long gamma-ray burst jets propagate from the central engine through and beyond the progenitor star. It employs 2.5D GRMHD simulations with adaptive mesh refinement on a MESA-derived 25 M_sun progenitor with a 5 M_sun black hole, spanning from the horizon to large radii to capture accretion, jet launching, and breakout. Across three magnetization models (unmagnetized, hybrid, and dipole), the results show that a magnetically saturated, MAD-like state yields high jet efficiency (eta > 50%), rapid breakout (t_bo ≈ 2.2 s), and a powerful jet (L_j ≈ 5×10^52 erg s^-1), while weaker or absent magnetic flux prevents breakout. These findings link engine magnetization and progenitor structure to observable GRB variability and afterglow characteristics, while highlighting the need for 3D, neutrino-transport-inclusive models to fully connect theory with observations.

Abstract

Long gamma-ray bursts (lGRB) are produced by relativistic jets arising from the collapse of massive stars. Such progenitor environments present complex physical conditions that are challenging to model by numerical simulations. The difficulty increases when solving the accretion process and propagation of the outflows, as it requires covering distances from the black hole horizon to beyond the progenitor star. General Relativistic Magnetohydrodynamic (GRMHD) simulations provide a convenient framework to study high-luminosity jets, where magnetic flux plays an important role in the process of jet launching from the central engine. To follow the propagation of the jet through and beyond its progenitor environment, we use multi-scale simulations (i.e., AMR-based). In this work, we report results of 2.5-dimensional GRMHD simulations of a lGRB progenitor. We present highly magnetized, weakly magnetized, and non-magnetized pre-collapse stars, and discuss the observational implications for lGRB jets.

The propagation of long GRB jets through and beyond its progenitor star

TL;DR

The paper investigates how long gamma-ray burst jets propagate from the central engine through and beyond the progenitor star. It employs 2.5D GRMHD simulations with adaptive mesh refinement on a MESA-derived 25 M_sun progenitor with a 5 M_sun black hole, spanning from the horizon to large radii to capture accretion, jet launching, and breakout. Across three magnetization models (unmagnetized, hybrid, and dipole), the results show that a magnetically saturated, MAD-like state yields high jet efficiency (eta > 50%), rapid breakout (t_bo ≈ 2.2 s), and a powerful jet (L_j ≈ 5×10^52 erg s^-1), while weaker or absent magnetic flux prevents breakout. These findings link engine magnetization and progenitor structure to observable GRB variability and afterglow characteristics, while highlighting the need for 3D, neutrino-transport-inclusive models to fully connect theory with observations.

Abstract

Long gamma-ray bursts (lGRB) are produced by relativistic jets arising from the collapse of massive stars. Such progenitor environments present complex physical conditions that are challenging to model by numerical simulations. The difficulty increases when solving the accretion process and propagation of the outflows, as it requires covering distances from the black hole horizon to beyond the progenitor star. General Relativistic Magnetohydrodynamic (GRMHD) simulations provide a convenient framework to study high-luminosity jets, where magnetic flux plays an important role in the process of jet launching from the central engine. To follow the propagation of the jet through and beyond its progenitor environment, we use multi-scale simulations (i.e., AMR-based). In this work, we report results of 2.5-dimensional GRMHD simulations of a lGRB progenitor. We present highly magnetized, weakly magnetized, and non-magnetized pre-collapse stars, and discuss the observational implications for lGRB jets.
Paper Structure (4 sections, 1 equation, 2 figures)

This paper contains 4 sections, 1 equation, 2 figures.

Table of Contents

  1. Introduction
  2. Methods
  3. Results
  4. Discussion and Conclusions

Figures (2)

  • Figure 1: Left panel: the evolution of the magnetic flux. Right panel: the jet efficiency. Model 1 is not reported in this figure because it is not magnetized.
  • Figure 2: Upper row: the density maps zoomed into the region of the stellar core $r \sim 10^8$ cm. We show the same snapshot at $t \sim 0.78$ s to compare the ejected outflows by the accretion process. Lower row: maps of the velocity magnitude $\Gamma u$. We show at different times and different zoom levels. The dashed circle in Model 3 represents the stellar boundary.