Hitomi Limits on the 3.5 keV signal.

http://iopscience.iop.org/article/10.3847/2041-8213/aa61fa
http://adsabs.harvard.edu/abs/2017ApJ...837L..15A

Hitomi Constraints on the 3.5 keV Line in the Perseus Galaxy Cluster

ADS: papers cited the Hitomi 3.5 keV paper
https://goo.gl/NHDreE