Pair Cascades initiated by ultra-high-energy gamma-rays from Galactic PeVatrons

Project Description:

The Large High Altitude Air Shower Observatory (LHAASO) has detected ~30 Galactic gamma-ray sources at extremely high energies above 100 TeV (100 x 10^{12} Electron Volt). In order to produce gamma-rays at those energies, these sources must be able to accelerate particles (electrons or protons) to at least 10^{15} eV = 1 PeV. Hence such sources are often referred to as PeVatrons. Gamma-rays at those extreme energies are susceptible to gamma-gamma-absorption on interstellar radiation fields, leading to electron-positron pair production (see Zhang and Guo 2026: ApJ, 1000, 19, https://iopscience.iop.org/article/10.3847/1538-4357/ae48f4). However, those secondary pairs will produce additional high-energy gamma-rays through Compton scattering, which can again be absorbed to produce more pairs, and so on, until the radiation produced is of sufficiently low energy to propagate freely through the Galaxy. This is called a pair cascade, and it is the goal of this M.Sc. project to develop a Monte-Carlo code to simulate the development of such cascades as TeV gamma-rays from Galactic PeVatrons propagate towards Earth. The M.Sc. project will focus on spectral signatures of the cascade. It can be naturally extended towards a Ph.D., where detailed spatial signatures ("pair halos") may be simulated, possibly placing strong constraints on interstellar magnetic fields, which are difficult to measure by other means. The code development may build on a code developed for the simulation of pair cascades initiated by very-high-energy gamma-rays from active galactic nuclei by Roustazadeh & Boettcher (2010: ApJ, 717, 468; 2011: ApJ, 728, 134; 2012: ApJ, 750, 26) and currently further extended by UJ Ph.D. student Mfuphi Ntshatsha (e.g., Ntshatsha, Boettcher, & Razzaque, 2025, proceedings of HEASA 2025: Online at https://pos.sissa.it/cgi-bin/reader/conf.cgi?confid=514, id.2). As that code is written in C, familiarity with that programming language will be advantageous.

Research Area:

Astrophysics

Project Level:

Masters

This Project Is Offered At The Following Node(s):

(NWU)