arXiv subjects

Emma Dreas

Publications and source records attributed to Emma Dreas.

4 recordsLinked to original sources

arXiv2026

Simulating the quasi-ballistic regime of a short Gamma-Ray Burst jet

This study extends the 3D magnetohydrodynamic (MHD) simulation of a jet emerging from a binary neutron star (BNS) merger presented in Pavan et al. (2023), in which an incipient jet was manually injected into the realistic environment imported from a previous general-relativistic MHD simulation of a merging BNS system. The jet evolution is followed up to almost 10 seconds without loss of resolution. Our results reveal that the jet faces challenges in penetrating the dense surroundings, leading to a barely successful outflow that exhibits structural asymmetries and low Lorentz factors. By the end of the extended simulation, 98% of the jet energy is converted to kinetic form and its angular structure is stabilized. The physical quantities inferred thus provide reliable inputs for afterglow emission calculations. This work demonstrates a method for simulating jets in 3D up to nearly ballistic regimes that is general and ready to be applied to any jet in a BNS merger context.

astro-ph.HE↗

arXiv2026

Evolution and afterglow emission of gamma-ray burst jets from binary neutron star mergers

Relativistic jets launched in binary neutron star (BNS) mergers are widely accepted as the engines powering most of the population of short gamma-ray bursts (GRBs). Understanding their structure and dynamics-particularly during and after breakout from the merger ejecta-is crucial for interpreting GRB afterglows, especially for off-axis observers. Traditional models often assume simple angular or radial jet profiles, potentially missing key features emerging for jets piercing through realistic environments. This work aims to investigate the formation and evolution of the jet structure as it propagates through a non-homogeneous, anisotropic BNS merger environment. We focus on how the interaction with the ambient medium shapes the jet's angular and velocity distributions and assess the impact of this realistic structure on the resulting afterglow light curves. We perform a series of 3D relativistic magnetohydrodynamic simulations of jets launched in post-merger environments, exploring different injection conditions. Simulations are evolved to late times, approaching the ballistic regime, where further dynamical evolution becomes negligible. From the resulting outflows, we extract energy and velocity profiles and compute multi-wavelength afterglow light curves using a semi-analytic model that includes radial stratification and the full 3D jet geometry. More energetic or earlier-launched jets drill more efficiently through the ejecta, but all develop asymmetries that leave clear imprints in the off-axis afterglow light curves. All models exhibit a complex multi-shock breakout structure responsible for an early, dimmer peak in the afterglow. Despite structural differences, all simulated jets are consistent with the observational data of the multi-messenger BNS merger event GW170817.

astro-ph.HE↗

arXiv2025

Role of injection parameters in jet propagation through realistic binary neutron star merger environments

After the first multi-messenger observation of a binary neutron star (BNS) merger powering a short-duration gamma-ray burst (GRB), GW170817-GRB 170817A, remarkable effort is ongoing to unravel the evolution of the collimated, relativistic outflow (or jet) that was launched during the merger and fed the GRB event, imprinting its angular structure onto the follow-up afterglow signal. Current theoretical models, based on relativistic magneto-hydrodynamic (RMHD) simulations, offer detailed insights into the launch and propagation processes that govern jet evolution. Notably, these simulations point out that jet injection parameters, such as luminosity, magnetization, power decay time scale, and launch time relative to merger, play a crucial role. However, the impact of these parameters is typically investigated within simplified jet propagation environments, lacking a direct connection with a realistic BNS merger aftermath. In this work, we present the first suite of 3D RMHD simulations exploring the influence of such parameters on the propagation of magnetized incipient GRB jets injected into magnetized environments directly imported from the outcome of a general-relativistic MHD BNS merger simulation. Our results demonstrate that, alongside the injection parameters, the BNS merger environment has a central role in shaping the overall jet evolution. Specifically, under identical jet parameters, the fate of an incipient jet (whether it successfully breaks out or becomes choked) depends strongly on the properties of such an environment. Further quantitative comparison between realistic and simplified environments reveals major differences, emphasizing the importance of incorporating the former for accurate modeling.

astro-ph.HE↗

arXiv2025

Approaching ballistic motion in 3D simulations of gamma-ray burst jets in realistic binary neutron star merger environments

Context. The concomitant observation of gravitational wave and electromagnetic signals from a binary neutron star (BNS) merger in 2017 confirmed that these events can produce relativistic jets responsible for short Gamma-Ray Bursts (sGRBs). The complex interaction between the jet and the surrounding post-merger environment shapes the angular structure of the outflow, which is then imprinted in the prompt and afterglow sGRB emission. Aims. The outcome of relativistic (magneto)hydrodynamic simulations of jets piercing through post-merger environments is often used as input to compute afterglow signals to be compared with observations. However, for reliable comparisons, the jet propagation should be followed until nearly ballistic regimes, in which the jet acceleration is essentially over and the angular structure is no longer evolving. This condition is typically reached in 2D simulations, but not in 3D. Our goal is to extend a (specific) jet simulation in 3D up to a nearly ballistic phase, analysing the overall dynamical evolution from the jet breakout. Methods. Our work is based on a previous 3D magnetohydrodynamic jet simulation employing a realistic environment imported from a BNS merger simulation, extended here far beyond the evolution time originally covered. After approximately 3 seconds of the jet evolution on the original spherical grid, we remap the system into a uniform Cartesian grid and reach about 10 seconds without loss of resolution. Results. The specific jet considered here struggles to pierce the dense surroundings, resulting in a rather asymmetrical emerging outflow with relatively low Lorentz factor. The analysis of the energy conversion processes and corresponding acceleration shows that at the end of our simulation 98% of the energy is in kinetic form. Moreover, at that time the angular structure is frozen. We thus obtain suitable inputs for...

astro-ph.HE↗