Characterizing decaying dark matter: X-ray emission from sterile neutrinos

Recently, an unknown emission line at E $\sim$3.5 keV from several astrophysical objects has been detected. The line is suggested to be originating from decaying dark matter particles. The results have drawn great attention from the astrophysics and particle physics community. Since the detected line is significantly weak there has also been a long debate over the origin of this mysterious signal. The most accepted scenario is a radiatively decaying sterile neutrino of 7.1 keV in mass producing a monochromatic 3.5 keV line, which is observable in X-ray energy ranges. The problem has not been settled and further observations from more objects are needed to verify the detection in order to constrain the physical properties and the nature of the signal. In this paper, we present the current situation and provide further insights into the subject.