X-ray observations of the Zwicky 3146 galaxy cluster reveal a 3.5 keV excess

Abstract

In this note, we present spectral fits of the well-documented sloshing cool-core cluster Zwicky 3146 ($z=0.291$), to test the existence of the highly speculated 3.5 keV line. We report excesses at $>3\ddot{I}ƒ$ significance at $E=3.575$ keV, yielding a flux $F=8.73_{-2.22}^{+2.17}$ $\times 10^{-6}$ photons cm${}^{-2}$ s${}^{-1}$, in \textit{XMM-Newton}, and $E=3.55$ keV, with a flux $F=10.0_{-2.96}^{+3.05}$ $\times 10^{-6}$ photons cm${}^{-2}$ s${}^{-1}$ in \textit{Chandra}. We explore the possibility that the 3.5 keV excess is correlated to the presence of cold gas within the cluster, based on optical and sub-mm literature analyses. Following the launch of the X-ray Imaging and Spectroscopy Mission (XRISM), high resolution spectroscopy ($\le 7$ eV) will reveal in unprecedented detail, the origin of this unidentified feature, for which Zwicky 3146 should be considered a viable target, due to the strength of the feature in two independent X-ray telescopes, opening a new window into plasma or charge exchange studies in galaxy clusters.

3 pages, 1 figure. Accepted for publication in the Research Notes of the AAS