Evidence for Strong Extragalactic Magnetic Fields from Fermi Observations of TeV Blazars

By Andrii Y. Neronov, I. Vovk. Science, 2010

878 citations recorded by the source corpus.

On the Origins of Magnetism The magnetic fields in galaxies and galaxy clusters are thought to result from the amplification of weak primordial magnetic fields, which, according to one class of theories, should exist in the voids between galaxies and galaxy clusters. Neronov and Vovk (p. 73) present evidence for the existence of intergalactic magnetic fields and derive a lower limit for their strength, based on an analysis of data from the Fermi Large Area Telescope. The results place constraints on magnetogenesis models and suggest that magnetic fields originated in the early universe before galaxy formation took place. An analysis of data from the Fermi Large Area Telescope sets a lower limit for the strength of intergalactic magnetic fields. Magnetic fields in galaxies are produced via the amplification of seed magnetic fields of unknown nature. The seed fields, which might exist in their initial form in the intergalactic medium, were never detected. We report a lower bound B ≥ 3 × 10−16 gauss on the strength of intergalactic magnetic fields, which stems from the nonobservation of GeV gamma-ray emission from electromagnetic cascade initiated by tera–electron volt gamma rays in intergalactic medium. The bound improves as λB−1/2 if magnetic field correlation length, λB, is much smaller than a megaparsec. This lower bound constrains models for the origin of cosmic magnetic fields.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/f1318b631b2159adc3ea6588fe638f014d403df7

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EVIDENCE FOR GAMMA-RAY HALOS AROUND ACTIVE GALACTIC NUCLEI AND THE FIRST MEASUREMENT OF INTERGALACTIC MAGNETIC FIELDS (2010, background): “Very recently, IGMF above 3 × 10−16 G were proposed as an explanation of non-observation by Fermi of several AGN known to be bright TeV sources (Neronov & Vovk 2010; see also Tavecchio et al. 2010).”
Simulations of magnetic fields in isolated disc galaxies (2012, background): “There have even been claims of an indirect detection of magnetic fields in cosmic voids (Neronov & Vovk 2010), although the robustness of this result is debated (Broderick et al. 2012).”
Can slow roll inflation induce relevant helical magnetic fields (2010, background): “Recently, using the absence of extended GeV emission around TeV blazar gamma-rays, a lower limit of 3× 10 Gauss on the strength of intergalactic magnetic fields was derived [5, 6, 7, 8].”
Extreme TeV blazars and the intergalactic magnetic field (2010, background): “…for deriving upper limits on the still unknown inte - c© 0000 RAS sity of the intergalactic magnetic field (IGMF, e.g. Kronberg 2001, Widrow 2002), based on the measured upper limits of the flux inthe GeV band (Neronov & Vovk 2010, Tavecchio et al. 2010b, hereafter T10b, Dolag et al. 2011).”
The Search for Spatial Extension in High-latitude Sources Detected by the Fermi Large Area Telescope (2018, methodology): “…to an excess in the GeV regime of γ-ray spectra, and the non-observation of this feature has been used to derive lower limits on the IGMF strength—or conversely, on the filling factor of the IGMF (Neronov & Vovk 2010; Dolag et al. 2011; Tavecchio et al. 2011; Taylor et al. 2011; Vovk et al. 2012).”
Ultra high energy cosmic rays: implications of Auger data for source spectra and chemical composition (2013, methodology): “At present this method only provided lower limits on the magnetic field B > (10−18 − 10−15) G [65, 66, 67], thereby leaving nG fields on a Mpc coherence scale as still allowed, although, as discussed above, it represents the highest values still compatible with current simulations of large scale”
The Astrophysics of Ultrahigh-Energy Cosmic Rays (2011, methodology): “15 G has been suggested using upper limits on the secondary emission of a few blazars Neronov & Vovk (2010) and by the apparent (and debated, see e.g., Neronov et al. 2011) detection of pair halos in stacked images of a large number of sources Ando & Kusenko (2010).”
Cosmological Magnetic Fields: Their Generation, Evolution and Observation (2013, background): “Another possibility to distinguish cosmological IGMF from the fields spread by galactic winds is to search for turbulence in the voids of LSS.”
BLAZARS AS ULTRA-HIGH-ENERGY COSMIC-RAY SOURCES: IMPLICATIONS FOR TeV GAMMA-RAY OBSERVATIONS (2011, background): “Extreme TeV blazars, in sources like 1ES 0229+200, 1ES 0347-121, H 2346-309, and 1ES 1101- 232 (Neronov & Vovk 2010), are extreme both in their deabsorbed TeV spectra and their quiescent, non-blazar-like behavior.”
Dark matter and fundamental physics with the Cherenkov Telescope Array (2012, background): “and lower limits lie many orders of magnitude below [153,154].”
Planck 2015 results: XIX. Constraints on primordial magnetic fields (2015, neutral): “A recent addition to the largescale magnetic field constraints comes from the interpretation of Fermi-LAT data (Neronov & Vovk 2010).”
Magnetic Fields in Galaxies (2010, background): “Recently Neronov & Vovk (2010) have set a lower limit of 3 10−16 G for large scale fields along the line of sight to two TeV blazar sources observed by the Fermi satellite, while Ando & Kusenko (2010) claim to have detected a field of 10−15G, also from Fermi .”