Abstract
One of the most promising ways to probe intergalactic magnetic fields (IGMFs) is through gamma rays produced in electromagnetic cascades initiated by high-energy gamma rays or cosmic rays in the intergalactic space. Because the charged component of the cascade is sensitive to magnetic fields, gamma-ray observations of distant objects such as blazars can be used to constrain IGMF properties. Ground-based and space-borne gamma-ray telescopes deliver spectral, temporal, and angular information of high-energy gamma-ray sources, which carries imprints of the intervening magnetic fields. This provides insights into the nature of the processes that led to the creation of the first magnetic fields and into the phenomena that impacted their evolution. Here we provide a detailed description of how gamma-ray observations can be used to probe cosmic magnetism. We review the current status of this topic and discuss the prospects for measuring IGMFs with the next generation of gamma-ray observatories.
Highlights
The advent of imaging air Cherenkov telescopes (IACTs) enabled the study of veryhigh-energy (VHE; E 1 TeV) processes involving gamma rays with unprecedented precision
If intergalactic magnetic fields (IGMFs) have been generated in the early Universe—called primordial magnetic fields (PMFs)—they have an impact on several cosmological aspects
The most widely studied beyond the Standard Model (BSM) processes that could interfere with the gamma-ray–IGMF framework we present here involve Lorentz invariance violation (LIV) and interactions with axion-like particles (ALPs)
Summary
The advent of imaging air Cherenkov telescopes (IACTs) enabled the study of veryhigh-energy (VHE; E 1 TeV) processes involving gamma rays with unprecedented precision. In cosmic voids, measurements are more difficult because of the low density of these regions This is where high-energy gamma rays from electromagnetic cascades excel: they provide tomographic information of the magnetic fields in these regions. Would indicate that seed magnetic fields originated in astrophysical objects, and were subsequently amplified through dynamo processes until they reached present-day levels of ∼1 μG in galaxies [52,57] Another way to constrain cosmic magnetic fields (or to explain certain observations) provides only upper bounds. If IGMFs have been generated in the early Universe—called primordial magnetic fields (PMFs)—they have an impact on several cosmological aspects First of all, they represent an additional constituent of the total energy of the Universe and, as such, have an impact on its evolution which results in manifold imprints onto the CMB (see [60] and the references therein).
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