In light of recent claims of the discovery of an unidentified emission line at \sim 3.55 keV in stacked XMM-Newton spectra for galaxy clusters , as well as XMM-Newton and Chandra spectra for the Milky Way and M31 , and the possible association of this line with a decaying dark matter ( DM - possibly sterile neutrino ) origin , we search for the presence of unidentified emission lines in deep Suzaku X-ray spectra for the central regions of the four X-ray brightest galaxy clusters : Perseus , Coma , Virgo and Ophiuchus .
We employ an optimized energy range for our analysis ( 3.2 - 5.3 keV ) that is relatively free of instrumental features , and a baseline plasma emission model that incorporates the abundances of elements with the strongest expected emission lines at these energies ( S , Ar , Ca ) as free parameters .
For the Perseus Cluster core , employing our baseline plasma model , we find evidence for an additional emission feature at an energy E = 3.51 ^ { +0.02 } _ { -0.01 } keV with a flux of 2.87 _ { -0.38 } ^ { +0.33 } \times 10 ^ { -7 } \text { ph } \text { s } ^ { -1 } \text { cm } ^ { -2 } \text { % arcmin } ^ { -2 } .
At slightly larger radii , we detect an emission line at 3.59 \pm 0.02 keV with a flux of 4.8 _ { -1.4 } ^ { +1.7 } \times 10 ^ { -8 } \text { ph } \text { s } ^ { -1 } \text { cm } ^ { -2 } \text { % arcmin } ^ { -2 } .
The energies and fluxes of these features are broadly consistent with previous claims , although the radial variation of the line strength appears in tension with standard dark matter model predictions .
Assuming a decaying DM origin for the Perseus emission features allows us to predict the energies and detected line fluxes for the other clusters in our sample .
Critically , we do not detect an emission feature at the predicted energy and line flux in the Coma , Virgo and Ophiuchus clusters .
The formal 99.5 per cent upper limits on the strengths of an emission line in each cluster are below the decaying DM model predictions , scaling from the Perseus Cluster center , apparently ruling the model out .
In the light of these results , which disfavor a decaying DM interpretation , we search for other explanations for the \sim 3.55 keV emission feature in Perseus .
Refitting the spectra with a more complex plasma model that allows the abundances of additional elements ( Cl , K , Ti and V ) to be free parameters removes the need for any unidentified line in the 3.5 - 3.6 keV region .
Our results suggest that systematic effects associated with modeling the complex projected spectra for the Perseus Cluster core , details of the assumed ionization balance , and errors in the predicted emissivities of individual spectral lines may in part be responsible for the \sim 3.5 keV feature .
The upcoming Astro-H satellite will allow us to explore the origins of this feature more robustly .