paper on keV sterile neutrinos [@2016arXiv160204816A].

We thank the anonymous referee for constructive comments that helped to improve the clarity of the paper. We thank J. Buchner, A. Del Moro, C. Pulsoni, and J. Ridl for helpful discussions. This research has made use of data obtained from the *Chandra* Data Archive, software provided by the *Chandra* X-ray Center (CXC) in the application package CIAO, NASA’s Astrophysics Data System, data and software provided by the High Energy Astrophysics Science Archive Research Center (HEASARC), which is a service of the Astrophysics Science Division at NASA/GSFC and the High Energy Astrophysics Division of the Smithsonian Astrophysical Observatory, the tools Veusz, the matplotlib library for Python, and TOPCAT. M.G. is supported by the National Aeronautics and Space Administration through Einstein Postdoctoral Fellowship Award Number PF-160137 issued by the *Chandra* X-ray Observatory Center, which is operated by the Smithsonian Astrophysical Observatory for and on behalf of the National Aeronautics Space Administration under contract NAS8-03060.

Dark matter mass profiles {#sec:acalc}
=========================

We assumed the cluster density follows an NFW profile [@1997ApJ...490..493N] depending on the radius r from the centre,

$$\rm{\rho(r)=\frac{\delta_c\rho_c}{r/r_s~(1+r/r_s)^2}}$$

$$\rm{\delta_c=\frac{500}{3}\times\frac{C^3}{ln(1+C)-C/(1+C)}}$$

where concentration C and radius $\rm{r_s}$ are empirical cluster specific values. C describes how strongly 