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

TL;DR

This study reports the detection of a 3.5 keV emission line in the galaxy cluster Zwicky 3146 using XMM-Newton and Chandra, suggesting potential links to cold gas or new physics, and highlights future high-resolution spectroscopy prospects.

Contribution

First detection of a 3.5 keV line in Zwicky 3146 with two X-ray telescopes, supporting further investigation into its origin and implications.

Findings

Excess at 3.575 keV with >3σ significance in XMM-Newton data.

Excess at 3.55 keV with >3σ significance in Chandra data.

Potential correlation between the 3.5 keV excess and cold gas presence.

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 $>3\sigma$ 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 ($\leq 7$ 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.