We recently detected an unidentified emission line at 3.55 keV in the stacked observations of 73 nearby galaxy clusters from the European Space Agency's XMM-Newton space telescope with 4-5 astrophysical sigma. The signal is also detected with ~ 3 sigma in the NASA's Chandra X-ray observations of the Perseus cluster. It is physically difficult to attribute this line to any known emission lines from known atomic transitions at that specific energy. An intriguing possibility is the decay of sterile neutrino, a long-sought dark matter particle candidate. In this case, the detected line energy corresponds to sterile neutrino mass of 7 keV. The mixing angle referred from the X-ray observations are consistent with the previous upper limits (shown in the figure below). Press releases on this work can be found at the Science, New Scientist, and Quanta magazines.
The figure shows the mysterious line at 3.55 keV observed in the stacked XMM-Newton observations of 73 galaxy clusters.
The mass-mixing angle refered from our X-ray observations and previous upper limits are shown in the figure.
Supernova explosions (SN) enrich the intra-cluster medium (ICM) by creating and dispersing metals. The recent method we developed allow to measure contribution of supernovae type Ia and core-collapse supernovae explosions by directly modeling X-ray observations. The method, has been implemented as an X-ray spectral fitting software XSPEC model, and called snapec.
The figure shows an application of snapec model to simulated Astro-H spectrum of A3112.