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Evidence for Gamma-ray Halos Around Active Galactic Nuclei and the First Measurement of Intergalactic Magnetic Fields

Ando, Shin’ichiro and Kusenko, Alexander (2010) Evidence for Gamma-ray Halos Around Active Galactic Nuclei and the First Measurement of Intergalactic Magnetic Fields. Astrophysical Journal Letters, 722 (1). L39-L44. ISSN 2041-8205.

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Intergalactic magnetic fields (IGMFs) can cause the appearance of halos around the gamma-ray images of distant objects because an electromagnetic cascade initiated by a high-energy gamma-ray interaction with the photon background is broadened by magnetic deflections. We report evidence of such gamma-ray halos in the stacked images of the 170 brightest active galactic nuclei (AGNs) in the 11 month source catalog of the Fermi Gamma-Ray Space Telescope. Excess over the point-spread function in the surface brightness profile is statistically significant at 3.5σ (99.95% confidence level), for the nearby, hard population of AGNs. The halo size and brightness are consistent with IGMF, B_(IGMF) ≈10^(–15) G. The knowledge of IGMF will facilitate the future gamma-ray and charged-particle astronomy. Furthermore, since IGMFs are likely to originate from the primordial seed fields created shortly after the big bang, this potentially opens a new window on the origin of cosmological magnetic fields, inflation, and the phase transitions in the early universe.

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Additional Information:© 2010 The American Astronomical Society. Received 2010 June 10; accepted 2010 September 1; published 2010 September 17. S.A. was supported by Japan Society for Promotion of Science and partially by NASA through the Fermi GI Program grant NNX09AT74G. A.K. was supported by DOE grant DE-FG03-91ER40662 and NASA ATP grant NNX08AL48G. A.K. thanks Aspen Center for Physics for hospitality.
Funding AgencyGrant Number
Japan Society for Promotion of ScienceUNSPECIFIED
Department of Energy (DOE)DE-FG03-91ER40662
Subject Keywords:galaxies: active; gamma rays: general; ISM: magnetic fields
Issue or Number:1
Classification Code:PACS: 98.54.Cm; 98.62.Ra; 98.70.Rz; 98.58.Ay; 98.62.Py
Record Number:CaltechAUTHORS:20101021-112323356
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Official Citation:Shin'ichiro Ando and Alexander Kusenko 2010 ApJ 722 L39. doi: 10.1088/2041-8205/722/1/L39
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:20467
Deposited By: Tony Diaz
Deposited On:12 Nov 2010 00:28
Last Modified:03 Oct 2019 02:10

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