Generation of 10(15)-10(17) eV photons by ultrahigh-energy cosmic rays in the Galactic magnetic field

It is shown that the expected dip in the diffuse photon spectrum above the threshold of e(+)e(-) pair production, i.e., at energies 10(15)-10(17) eV, may be absent due to the synchrotron radiation by the electron component of the extragalactic ultrahigh-energy cosmic rays (UHE CRs) in the Galactic m agnetic field. The mechanism we propose requires small (< 2 x 10(-12) G) ex tragalactic magnetic fields and a large photon fraction in the UHE CRs. For a typical photon flux expected in top-down scenarios of UHE CRs, the predi cted flux in the region of the dip is close to the existing experimental li mit. The sensitivity of our mechanism to the extragalactic magnetic field m ay be used to improve existing bounds on the latter by two orders of magnit ude. (C) 1999 American Institute of Physics. [S0021-3640(99)00220-0].