Physics of cosmological cascades and observable properties

T. Fitoussi (1) , R. Belmont (1) , J. Malzac (1) , Alexandre Marcowith (2) , Johann Cohen-Tanugi (2) , P. Jean (1)

1 IRAP - Institut de recherche en astrophysique et planétologie
2 LUPM - Laboratoire Univers et Particules de Montpellier

TeV photons from extragalactic sources are absorbed in the intergalactic medium and initiate electromagnetic cascades. These cascades offer a unique tool to probe the properties of the universe at cosmological scales. We present a new Monte Carlo code dedicated to the physics of such cascades. This code has been tested against both published results and analytical approximations, and is made publicly available. Using this numerical tool, we investigate the main cascade properties (spectrum, halo extension and time delays), and study in detail their dependence on the physical parameters (extragalactic magnetic field, extragalactic background light, source redshift, source spectrum and beaming emission). The limitations of analytical solutions are emphasized. In particular, analytical approximations account only for the first generation of photons and higher branches of the cascade tree are neglected.

Mots clés: gamma-rays: general; astroparticles physics; extra-galactic magnetic field; scattering; relativistic processes; astroparticle physics; magnetic fields; opacity; cosmic background radiation; gamma-rays: diffuse background; cascade: electromagnetic; gamma ray: VHE; magnetic field; Monte Carlo; background; time delay; redshift; halo; spectrum; tree approximation

Domaines: Astrophysique [astro-ph]

T. Fitoussi, R. Belmont, J. Malzac, Alexandre Marcowith, Johann Cohen-Tanugi, et al.. Physics of cosmological cascades and observable properties. Monthly Notices of the Royal Astronomical Society, 2017, 466 (3), pp.3472-3487. ⟨10.1093/mnras/stw3365⟩. ⟨hal-01554935⟩