Search for electromagnetic super-preshowers using gamma-ray telescopes.

Any considerations on propagation of particles through the Universe must involve particle interactions: processes leading to production of particle cascades. While one expects existence of such cascades, the state of the art cosmic-ray research is oriented purely on a detection of single particles, gamma rays or associated extensive air showers. The natural extension of the cosmic-ray research with the studies on ensembles of particles and air showers is being proposed by the Cosmic-Ray Extremely Distributed Observatory (CREDO) Collaboration. Within the CREDO strategy the focus is put on generalized super-preshowers (SPS): spatially and/or temporally extended cascades of particles originated above the Earth atmosphere, possibly even at astrophysical distances. With CREDO we want to find out whether SPS can be at least partially observed by a network of terrestrial and/or satellite detectors receiving primary or secondary cosmic-ray signal. This paper addresses electromagnetic SPS, e.g. initiated by very high energy photons interacting with the cosmic microwave background, and the SPS signatures that can be seen by gamma-ray telescopes, exploring the example of Cherenkov Telescope Array. The energy spectrum of secondary electrons and photons in an electromagnetic super-preshower might be extended over a wide range of energy, down to TeV or even lower, as it is evident from the simulation results. This means that electromagnetic showers induced by such particles in the Earth atmosphere could be observed by imaging atmospheric Cherenkov telescopes. We present preliminary results from the study of response of the Cherenkov Telescope Array to SPS events, including the analysis of the simulated shower images on the camera focal plane and implemented generic reconstruction chains based on the Hillas parameters. The eventual detection of super-preshowers will mean opening a new window to the Universe - a new chance for solving the most pending issues of contemporary astrophysics.