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We develop the connection between intergalactic helical magnetic fields and parity odd signatures in the diffuse gamma ray sky. We find that the location and the amplitude of a peak in a parity odd correlator, $Q(R)$, can be used to infer…

Cosmology and Nongalactic Astrophysics · Physics 2015-06-22 Hiroyuki Tashiro , Tanmay Vachaspati

Large-scale intergalactic magnetic fields may contain a mixture of galactic and cosmogenic contributions, that can be probed via observations of $\gamma$-ray "echo" - a delayed emission from electromagnetic cascades initiated by the highest…

High Energy Astrophysical Phenomena · Physics 2026-02-10 Ievgen Vovk

The presence of non-zero helicity in intergalactic magnetic fields (IGMF) has been suggested as a clear signature for their primordial origin. We extend a previous analysis of diffuse Fermi-LAT gamma-ray data from 2.5 to more than 11 years…

High Energy Astrophysical Phenomena · Physics 2020-11-06 M. Kachelriess , B. C. Martinez

We determine the effect of intergalactic magnetic fields on the distribution of high energy gamma rays by performing three-dimensional Monte Carlo simulations of the development of gamma-ray-induced electromagnetic cascades in the…

High Energy Astrophysical Phenomena · Physics 2016-10-19 Rafael Alves Batista , Andrey Saveliev , Guenter Sigl , Tanmay Vachaspati

We search for observational signatures of magnetic helicity in data from all-sky radio polarization surveys of the Milky Way Galaxy. Such a detection would help confirm the dynamo origin of the field and may provide new observational…

Astrophysics of Galaxies · Physics 2020-10-14 J. L. West , R. N. Henriksen , K. Ferrière , A. Woodfinden , T. Jaffe , B. M. Gaensler , J. A. Irwin

We explore potential of current and next-generation gamma-ray telescopes for the detection of weak magnetic fields in the intergalactic medium. We demonstrate that using two complementary techniques, observation of extended emission around…

Cosmology and Nongalactic Astrophysics · Physics 2009-12-31 A. Neronov , D. Semikoz

The existence of a cosmological magnetic field could be revealed by the effects of non-trivial helicity on large scales. We evaluate a CP odd statistic, $Q$, using gamma ray data obtained from Fermi satellite observations at high galactic…

Cosmology and Nongalactic Astrophysics · Physics 2014-09-12 Hiroyuki Tashiro , Wenlei Chen , Francesc Ferrer , Tanmay Vachaspati

We report a measurement of intergalactic magnetic fields using combined data from Atmospheric Cherenkov Telescopes and Fermi Gamma-Ray Space Telescope, based on the spectral data alone. If blazars are assumed to produce both gamma rays and…

High Energy Astrophysical Phenomena · Physics 2012-04-03 Warren Essey , Shin'ichiro Ando , Alexander Kusenko

The presence of delayed GeV emission after a strong transient, such as a GRB (Gamma-Ray Burst), in the VHE (Very-High Energy, $E>100$ GeV) band can be the signature of a non-zero magnetic field in the intergalactic medium. We used a…

High Energy Astrophysical Phenomena · Physics 2023-04-05 Paolo Da Vela , Guillem Martí-Devesa , Francesco Gabriele Saturni , Peter Veres , Antonio Stamerra , Francesco Longo

We study the characteristic size and shape of idealized blazar-induced cascade halos in the $1-100 \, {\rm GeV}$ energy range assuming various non-helical and helical configurations for the intergalactic magnetic field (IGMF). While the…

Cosmology and Nongalactic Astrophysics · Physics 2015-09-30 Andrew J. Long , Tanmay Vachaspati

In over two years of operation Fermi-LAT has revolutionized our knowledge of the gamma-ray sky. Interstellar gamma rays are part of this new era and allow unprecedented tests for models of cosmic rays in the Galaxy. The extension to lower…

High Energy Astrophysical Phenomena · Physics 2017-08-23 A. W. Strong

Delayed "pair echo" signal from interactions of very-high-energy gamma rays in the intergalactic medium can be used for detection of the inter-galactic magnetic field (IGMF). We use the data of Fermi/LAT telescope coupled with LHAASO…

High Energy Astrophysical Phenomena · Physics 2023-06-14 Ie. Vovk , A. Korochkin , A. Neronov , D. Semikoz

A cosmological origin of the magnetic fields in large scale structures of the Universe would require a non-negligible magnetic field in cosmic voids, which, however, remains undetected. Gamma-ray emission from gamma-ray bursts (GRBs) offers…

High Energy Astrophysical Phenomena · Physics 2026-02-24 Lea Burmeister , Paolo Da Vela , Francesco Longo , Guillem Marti-Devesa , Manuel Meyer , Francesco Saturni , Antonio Stamerra , Peter Veres

Inter-galactic magnetic fields can imprint their structure on the morphology of blazar-induced gamma ray halos. We show that the halo morphology arises through the interplay of the source's jet and a two-dimensional surface dictated by the…

High Energy Astrophysical Phenomena · Physics 2017-05-04 Francis Duplessis , Tanmay Vachaspati

Using one-dimensional models, we show that a helical magnetic field with an appropriate sign of helicity can compensate the Faraday depolarization resulting from the superposition of Faraday-rotated polarization planes from a spatially…

Cosmology and Nongalactic Astrophysics · Physics 2014-04-23 Axel Brandenburg , Rodion Stepanov

TeV emission from blazars can be used to probe the intergalactic magnetic fields and measure their intensity, coherence length, and helicity. Intergalactic magnetic fields deflect the electron-positron pairs produced by very-high-energy…

High Energy Astrophysical Phenomena · Physics 2018-11-15 Wenlei Chen , Manel Errando , James H. Buckley , Francesc Ferrer

Very-high energy observations of blazars can be used to constrain the strength of the intergalactic magnetic field. A simplifying assumption which is often made is that of a magnetic field of constant strength composed by randomly oriented…

Cosmology and Nongalactic Astrophysics · Physics 2015-06-17 Chiara Caprini , Stefano Gabici

The extragalactic magnetic field could be detected by searching for signatures of the electromagnetic cascade initiated by high-energy photons on the intergalactic radiation and deflected by the field. This process produces a time delay and…

Cosmology and Nongalactic Astrophysics · Physics 2025-12-04 Boris Stern , Igor Tkachev

Helical intergalactic magnetic fields at the $\sim 10^{-14}~{\rm G}$ level on $\sim 10~{\rm Mpc}$ length scales are indicated by current gamma ray observations. The existence of magnetic fields in cosmic voids and their non-trivial helicity…

Cosmology and Nongalactic Astrophysics · Physics 2017-03-15 Tanmay Vachaspati

Combined data from gamma-ray telescopes and cosmic-ray detectors have produced some new surprising insights regarding intergalactic and galactic magnetic fields, as well as extragalactic background light. We review some recent advances,…

High Energy Astrophysical Phenomena · Physics 2015-06-05 Alexander Kusenko
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