ИСТИНА

During this talk, we will describe, theoretically and through Monte-Carlo simulations, the formation of the 511 keV annihilation line due to photon-photon interacting very close to black hole horizons. Indeed, thermal photons in the Compton cloud very close to the horizon, interact with photons coming from far away, and "seen" highly blue-shifted, potentially above MeV energies. This effect results in the creation of electron-positron pairs, followed by the prompt annihilation of the created positrons with the Compton cloud electrons. Occurring at different radius from the horizon, the created annihilation line is seen by an Earth observer not as a line but rather as a bump at energies around (511/z) keV, where z~20 is a typical gravitational redshift experienced by the created annihilation-line photons when they emerge. This bump around 20 keV, that we derived analytically and confirmed through MC simulations, is thus similar to the so-called reflection bump observed in many Black Hole systems. This transient feature may be a Black Hole signature which should occur in any accreting BH system, either galactic or extragalactic. We will also explore observational evidences for this feature in several galactic BH systems.