People · Undergraduate intern

Ioannis Riganas

COSMOS, Research Center for Astronomy and Applied Mathematics (RCAAM), Academy of Athens · Intern · Πρακτική άσκηση

Completed August 2026

Research

Internship work

Jets · simulations

Poynting-flux jets with BHAC

Simulations of a magnetically dominated jet, calibrated to a McKinney-type Poynting jet with target magnetization σ = 10, injected through an inner boundary at r = 1000 M (500 r_s) and followed out to 20 000 M. The jet is launched within a 7° core that tapers to an edge at 10°, and a passive tracer follows the jet material as it mixes with its surroundings.

Jets · energetics

Angular structure and engine duration

From the completed runs, the angular distribution of the outflowing energy, dE/dΩ, is measured far from the injection region, separating the jet material from the shocked surroundings with the tracer. The energy flux is also recorded at several extraction radii to compare the duration of the energy pulse with the engine time, as a proxy for gamma-ray burst durations.

Jets · semi-analytic

Magnetically driven jet solutions

In parallel, the semi-analytic AV24 jet model is solved as a system of ODEs, searching for magnetically dominated solutions that pass smoothly through the critical points of the flow. Latin-hypercube sampling of the free parameters gives a better coverage of the parameter space.

Simulations

Movies

A Poynting jet launched into a low-density exterior from a compact initial magnetosphere, up to t = 20 000 M. Panels: density, jet energy flux weighted by the tracer, Lorentz factor, comoving magnetization, jet tracer and specific enthalpy. BHAC simulation · inner boundary r = 1000 M

The McKinney-calibrated Poynting jet with target σ = 10 drilling through a denser ambient medium, with the same set of quantities. BHAC simulation · inner boundary r = 1000 M · domain to r = 20 000 M

Figures

Jet structure

Azimuthal magnetic field at the inner boundary as a function of angle from the jet axis — The azimuthal magnetic field injected at the inner boundary (r = 1000 M): nearly constant across the 7° core, falling smoothly to zero at the jet edge at 10°.

Outflowing energy per solid angle versus polar angle at r = 9000 M, total and tracer-weighted — Angular energy structure at r = 9000 M. The total outward dE/dΩ stays flat, while the tracer-weighted jet energy is confined near the axis and drops steeply beyond about 30°.

Interactive: density, pressure, Lorentz factor, magnetization, tracer and mixing across the jet at r = 9000 M; pick the snapshot time at the top right. Open full screen ↗

Interactive: the jet energy flux at the engine and at several extraction radii against retarded time (left), and the duration containing 90% of the energy, T90, against extraction radius compared with the engine T90 (right). Open full screen ↗

Figures

Semi-analytic jet model

Twelve polar maps of the AV24 jet solution: density, pressure, Lorentz factor, velocities, magnetic field components — The AV24 jet solution in polar coordinates, from 2 to 3000 r_s: density, pressure, ξ, Lorentz factor, velocity and magnetic field components. The dashed curve is the 5% validity surface.

Radial profiles of the AV24 jet solution at 5 degrees from the axis — Radial profiles of the same solution at θ ≈ 5°: the flow accelerates to a Lorentz factor of about 60 as the magnetic field is converted into bulk motion.