Consistency of Hitomi, XMM-Newton and Chandra 3.5 keV data from Perseus

TL;DR

This study reconciles previous 3.5 keV excess observations in Perseus by linking AGN spectral dips to diffuse emission features, supported by high-resolution Hitomi data and dark matter models.

Contribution

It demonstrates that the 3.5 keV feature can be explained by AGN spectral dips and fluorescent dark matter models, resolving previous observational inconsistencies.

Findings

Hitomi data shows no excess at 3.5 keV in diffuse emission.

Chandra data reveals a dip at 3.54 keV in the AGN spectrum.

Scaling the dip explains the diffuse excess observed by XMM-Newton.

Abstract

\emph{Hitomi} observations of Perseus with the Soft X-ray Spectrometer (SXS) provide a high-resolution look at the 3.5 keV feature reported by multiple groups in the Perseus cluster. The \emph{Hitomi} spectrum -- which involves the sum of diffuse cluster emission and the point-like central Active Galactic Nucleus (AGN) -- does not show any excess at $E \sim 3.5 {\rm keV}$, giving an apparent inconsistency with previous observations of excess diffuse emission. We point out that 2009 \emph{Chandra} data reveals a strong dip in the AGN spectrum at $E = (3.54 \pm 0.02) {\rm keV}$ (cluster frame) -- the identical energy to the diffuse excess observed by \emph{XMM-Newton}. Scaling this dip to the 2016 AGN luminosity and adding it to the diffuse \emph{XMM-Newton} excess, this predicts an overall dip in the SXS field of view of $(-5.9 \pm 4.4) \times 10^{-6} \, {\rm ph} \, {\rm cm}^{-2} \, {\rm s}^{-1}$ at $E= 3.54$ keV -- a precise match to the \emph{Hitomi} data when broadened by the dark matter virial velocity. We describe models of Fluorescent Dark Matter that can reproduce this physics, in which dark matter absorbs and then re-emits 3.5 keV photons emitted from the central AGN.