Wednesday, June 26, 2013

1306.5865 (Olga Mena et al.)

Hints of an axion-like particle mixing in the GeV gamma-ray blazar data?    [PDF]

Olga Mena, Soebur Razzaque
Axion-Like Particles (ALPs), if exist in nature, are expected to mix with photons in the presence of an external magnetic field. The energy range of photons which undergo strong mixing with ALPs depends on the ALP mass, on its coupling with photons as well as on the external magnetic field and particle density configurations. Recent observations of blazars by the Fermi Gamma-Ray Space Telescope in the 0.1-300 GeV energy range show a break in their spectra in the 1-10 GeV range. We have modeled this spectral feature for the flat-spectrum radio quasar 3C454.3 during its November 2010 outburst, assuming that a significant fraction of the gamma rays convert to ALPs in the large scale jet of this blazar. Using theoretically motivated models for the magnetic field and particle density configurations in the kiloparsec scale jet, outside the broad-line region, we find an ALP mass $m_a\sim (1-3)\cdot 10^{-7}$ eV and coupling $g_{a\gamma} \sim (1-3)\cdot 10^{-10}$ GeV$^{-1}$ after performing an illustrative statistical analysis of spectral data in four different epochs of emission. The precise values of $m_a$ and $g_{a\gamma}$ depend weakly on the assumed particle density configuration and are consistent with the current experimental bounds on these quantities. We find that the ALP-photon mixing effect on the GeV spectra may not be washed out for any reasonable estimate of the magnetic field in the intergalactic media.
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