2015/05/31 by Andrew J. Long, Tanmay Vachaspati
Physics and Astronomy · #Astrophysics and Cosmic Phenomena #Blazar #Cascade #Coherence (philosophical gambling strategy) #Dark Matter and Cosmic Phenomena #Galactic halo #Halo #Helicity #Intergalactic travel #Magnetic field #Neutrino Physics Research #astro-ph.CO #astro-ph.GA #astro-ph.HE
paper · pdf · doi:10.1088/1475-7516/2015/09/065
v3 - 33 pages, 14 figures; reduced file size; matches JCAP version
arxiv created 2015/09/29 · openalex publication_date 2015/09/29 · arxiv updated 2015/09/30 · openalex created_date 2020/11/23 · openalex updated_date 2026/08/06
We study the characteristic size and shape of idealized blazar-induced cascade halos in the 1–100,GeV energy range assuming various non-helical and helical configurations for the intergalactic magnetic field (IGMF). While the magnetic field creates an extended halo, the helicity provides the halo with a twist. Under simplifying assumptions, we assess the parameter regimes for which it is possible to measure the size and shape of the halo from a single source and then to deduce properties of the IGMF. We find that blazar halo measurements with an experiment similar to Fermi-LAT are best suited to probe a helical magnetic field with strength and coherence length today in the ranges 10 −17 ≲ B 0 / Gauss ≲ 10 −13 and 10 Mpc ≲ λ ≲ 10 Gpc where ℋ ∼ B 0 2 / λ is the magnetic helicity density. Stronger magnetic fields or smaller coherence scales can still potentially be investigated, but the connection between the halo morphology and the magnetic field properties is more involved. Weaker magnetic fields or longer coherence scales require high photon statistics or superior angular resolution.