Search for spectral features in extragalactic background light with gamma-ray telescopes

A. Korochkin, A. Neronov, D. Semikoz

Published 2019-06-28Version 1

Cumulative optical / infrared emission from galaxies accumulated over cosmological time scales, the Extragalactic Background Light (EBL), could be probed by complementary techniques of direct observations and source counting in the visible / infrared and via its imprint on the signal of distant active galactic nuclei in gamma-rays. We compare the visible / infrared measurements with the gamma-ray constraints and study if the discrepancies of the measurements with different methods could be due to the presence of features in the EBL spectrum localised in the micron wavelength range. We combine data on time-averaged spectra of selected blazars obtained by Fermi and ground-based \gr\ telescopes and model the effect of absorption on EBL while allowing for existence of a previously unaccounted spectral feature. We show that previously reported "excess" EBL flux in $\sim 1$~micron wavelength range is consistent with gamma-ray measurements, if the excess has the form of a narrow feature of the width $\delta \lambda < \lambda$ and overall flux of up to 15 nW/(cm$^2$ sr) above the "minimal" EBL estimated from the visible / infrared source counts. Such "bump-like" spectral feature could originate e.g. from decaying dark matter particles, or axions or peculiar astrophysical processes in the course of star formation history. We discuss possibilities for the search of spectral features in the EBL with Cherenkov Telescope Array.