There have been several reports of a detection of an unexplained excess of X-ray emission at $simeq$ 3.5 keV in astrophysical systems. One interpretation of this excess is the decay of sterile neutrino dark matter. The most influential study to date analysed 73 clusters observed by the XMM-Newton satellite. We explore evidence for a $simeq$ 3.5 keV excess in the XMM-PN spectra of 117 redMaPPer galaxy clusters ($0.1 < z < 0.6$). In our analysis of individual spectra, we identify three systems with an excess of flux at $simeq$ 3.5 keV. In one case (XCS J0003.3+0204) this excess may result from a discrete emission line. None of these systems are the most dark matter dominated in our sample. We group the remaining 114 clusters into four temperature ($T_{rm X}$) bins to search for an increase in $simeq$ 3.5 keV flux excess with $T_{rm X}$ - a reliable tracer of halo mass. However, we do not find evidence of a significant excess in flux at $simeq$ 3.5 keV in any $T_{rm X}$ bins. To maximise sensitivity to a potentially weak dark matter decay feature at $simeq$ 3.5 keV, we jointly fit 114 clusters. Again, no significant excess is found at $simeq$ 3.5 keV. We estimate the upper limit of an undetected emission line at $simeq$ 3.5 keV to be $2.41 times 10^{-6}$ photons cm$^{-2}$ s$^{-1}$, corresponding to a mixing angle of $sin^2(2theta)=4.4 times 10^{-11}$, lower than previous estimates from cluster studies. We conclude that a flux excess at $simeq$ 3.5 keV is not a ubiquitous feature in clusters and therefore unlikely to originate from sterile neutrino dark matter decay.
تحميل البحث