2009 Fermi Symposium, Washington, D.C., Nov. 2-5 6 if photon/axion mixing occurs in the IGMFs, then a mixing in the source will be at work as well. In par- ticular, for axion masses of the order or 10 − 10 eV, the induced effect is expected to be present in the gamma ray energy range. Since photon/axion mixing in both the source and the IGM are expected to be at work over several decades in energy, it is clear that a joint effort of Fermi and current IACTs is needed. The Fermi/LAT instru- ment is expected to play a key role, since it will detect thousands of AGNs (up to z ∼ 5), at energies where the EBL is not important. By the other hand, IACTs will be specially important at higher energies ( > 300 GeV), where the EBL is present. Main caveats: the effect of photon/axion oscillations could be attributed to conventional physics in the source and/or propagation of the gamma-rays towards the Earth. However, we believe that detailed observa- tions of AGNs at different redshifts and different flar- ing states could be successfully used to identify the signature of an effective photon/axion mixing. 10 2 10 3 Energy [GeV] 10 -15 10 -14 10 -13 10 -12 10 -11 10 -10 d F /dE [GeV GLYPH<a0> 1 cm GLYPH<a0> 2 s GLYPH<a0> 1 ] 3C279, Kneiske+04 bestfit, B=0.1nG measured EBL corrected EBL+axions corrected FIG. 5: Effect of the existence of ALPs in the intrinsic spectrum of 3C 279, assuming the fiducial model given in Table I and a Kneiske best-fit model for the EBL. Blue points correspond to observational data taken with the MAGIC telescope [28]. astro-ph/0502177 [1] S´ anchez-Conde M. A., Paneque D., Bloom E., Prada F. and Dom´ınguez A., 2009, Phys. Rev. D , 79, 123511 [2] Peccei R. D. and Quinn H. R., 1977, Phys. Rev. Lett. , 38 , 1440 [3] Dicus D. A., Kolb E. W., Teplitz V. L. and Wagoner R. V., 1978, Phys. Rev. D , 18 , 1829 [20] Kneiske T. M., Bretz T., Mannheim K. and Hartmann D. H., 2004, A&A , 413 , 807 [21] Acciari V. A., 2009, ApJ , 693 , L104 [22] Aliu E. et al., 2009, ApJ , 692 , L29 [23] Neshpor Y. I., Stepanyan A. A., Kalekin O. P., Fomin V. P., Chalenko N. N. & Shitov V. G. 1998, Astron. Lett. , 24 , 134 [4] Sikivie P., 1983, Phys. Rev. Lett. , 51 , 1415 [Erratum ibid., 1984, Phys. Rev. Lett. , 52 , 695 [24] Stepanyan A. A., Neshpor Y. I., Andreeva N. A., Kalekin O. P., Zhogolev N. A., Fomin V. P.& Shitov V. G., 2002, Astron. Rep. , 46 , 634 [5] Andriamonje S. et al, 2007, JCAP , 0704 , 010 [6] Duffy L. D. et al., 2006, Phys. Rev. D , 74 , 012006 [7] Hooper D. and Serpico P., 2007, Phys. Rev. Lett. , 99 , 231102 [8] De Angelis A., Roncadelli M. and Mansutti O., 2007, Phys. Rev. D , 76 , 121301 [9] Hochmuth K. A., Sigl G., 2007, Phys. Rev. D , 76 , 123011 [25] Levenson L. R. & Wright E. L., 2008, ApJ , 683 , 585 [26] Krennrich, Dwek and Imran, 2008, ApJ , 689 , L93 [27] S´ anchez-Conde M. A. & Dom´ınguez A., in prep. [28] Albert et al., 2008, Science , 320, 1752 [29] At present, a concise modeling of this effect is still very dependent on the largely unknown morphology of the magnetic field in the galaxy. Furthermore, in the most optimistic case, it would produce a photon flux enhancement of ∼ 3% of the initial photon flux emitted by the source [10]. [10] Simet M., Hooper D. and Serpico P., 2008, Phys. Rev. D , 77 , 063001 [11] Mirizzi A., Raffelt G. G. and Serpico P., 2007, Phys. Rev. D , 76 , 023001 [12] Lorentz E. et al., 2004, New Astron. Rev. , 48 , 339 [13] Hinton J. A., 2004, New Astron. Rev. , 48 , 331 [14] Weekes T. C. et al., 2002, Astropart. Phys. , 17 , 221 [30] Note, however, that the attenuation starts to decrease at higher energies ( > 10 GeV) gradually, the reason being the crucial role of the Cotton-Mouton term, which makes the efficiency of the source mixing to decrease as the energy increases. See Ref. [1] for de- tails. [31] We refer to Ref. [1] for a detailed description of the model and the related equations. [15] Enomoto R. et al., 2002, Astropart. Phys. , 16 , 235 [16] Gehrels N. and Michelson P., 1999, Astropart. Phys. , 11 , 277 [17] Hartmann et al., 2001, ApJ , 553 , 683 [18] Kusunose M. and Takahara F., 2008, ApJ , 682 [19] Primack J.R., 2005, Proceedings of the Gamma 2004 Symposium on High Energy Gamma Ray As- tronomy , 26-30 July 2004, Heidelberg, Germany, eConf C091122