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Astrophysics, High Energy Astrophysical Phenomena, astro-ph.HE
Abstract:
The acceleration cites of ultra-high-energy (UHE) protons can be traced by
the footprint left by these particles propagating through cosmic microwave
background (CMB) radiation. Secondary electrons produced in extended region of
several tens of Mpc emit their energy via synchrotron radiation predominantly
in the initial direction of the parent protons. It forms a non-variable and
compact (almost point-like) source of high energy gamma rays. The importance of
this effect is increased for cosmologically distant objects; because of severe
energy losses, UHE protons cannot achieve us even in the case of extremely weak
intergalactic magnetic fields. Moreover, at high redshifts the energy
conversion from protons to secondary particles becomes significantly more
effective due to the denser and more energetic CMB in the past. This increases
the chances of UHE cosmic rays to be traced by the secondary synchrotron gamma
radiation. We discuss the energy budget and the redshift dependence of the
efficiency of energy transfer from UHE protons to synchrotron radiation. The
angular and spectral distributions of radiation in the gamma- and X-ray energy
bands are calculated and discussed in the context of their detectability by
Fermi LAT and Chandra observatories.
