Speaker
Description
In extreme astrophysical environments such as neutron stars, pulsars and magnetars, magnetic fields can reach strengths as high as 1015 Gauss. Due to the fast rotation of the star, a very large electric field is associated with these strong magnetic fields which accelerates charged particles to energies from GeV to TeV and provides an excellent environment for so-called QED shower [1-2]. Subject to an intense electromagnetic field, an electron can emit high-energy photons (non-linear Compton scattering) that can decay into an electron-positron pair (non-linear Breit-Wheeler process), further contributing to the shower. It will develop until the emitted photon does have not enough energy to decay and the remaining photons will escape thus providing the main source of radiation from the magnetized environments.
An analytical model of the shower characteristics has been proposed in [3] but shown to be inadequate for quantitative predictions [4]. 30 years later, the number of produced pairs as a function of the interaction time, the initial particle energy and the magnetic field intensity is identified using a different approach based on our previous work [5]. Two scaling laws respectively valid at short times (before the electron distribution has significantly cooled down) and at long times (when the majority of the incident particle energy is exhausted) are derived.
A systematic study using a Monte Carlo code shows excellent agreement with our model predictions for the photon energy spectrum and evolution of the number of pairs. The proposed scalings laws are also applied to a time-dependent field and show excellent agreement with the particle-in-cell code SMILEI [5] for laser-particle scattering. The model has practical applications for beam-beam interaction, laser-driven showers in the laboratory, astrophysical observations of pulsar radiation or astrophysics simulations.
[1] Goldreich & Julian (1969). ApJ 157 , 869
[2] Daugherty & Harding (1982). ApJ 252 , 337
[3] Akhiezer et al. (1994). Phys. G Nucl. Part. Phys. 20 ,1499
[4] Anguelov & Vankov (1999) J. Phys. G: Nucl. Part. Phys. 25 , 1755
[5] Pouyez et al. (2024), arXiv preprint arXiv:2402.04501
[6] Derouillat et al. (2018), Comput. Phys. Commun. 222 , 351
