New emission line at ~3.5 keV - observational status, connection with radiatively decaying dark matter and directions for future studies

Abstract

Recent works of Bulbul et al. (2014) and Boyarsky et al. (2014), claiming the detection of the extra emission line with energy ∼3.5 keV in X-ray spectra of certain clusters of galaxies and nearby Andromeda galaxy, have raised a considerable interest in astrophysics and particle physics communities. A number of new observational studies claim detection or non-detection of the extra line in X-ray spectra of various cosmic objects. In this review I summarise existing results of these studies, overview possible interpretations of the extra line, including intriguing connection with radiatively decaying dark matter, and show future directions achievable with existing and planned X-ray cosmic missions.