Morphology of blazar-induced gamma ray halos due to a helical intergalactic magnetic field

作者：Long Andrew J^*; Vachaspati Tanmay

来源：Journal of Cosmology and Astroparticle Physics, 2015, 2015(9): 065.

DOI：10.1088/1475-7516/2015/09/065

• extragalactic magnetic fields
• cosmic magnetic fields theory
• gamma ray theory
• primordial magnetic fields

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) less than or similar to B-0/Gauss less than or similar to 10(-13) and 10 Mpc less than or similar to lambda less than or similar to 10 Gpc where Script H similar to B-0(2)/lambda 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.

• 出版日期2015-9