Searches for 3.5 keV Absorption Features in Cluster AGN Spectra

TL;DR

This study searches for a potential 3.5 keV absorption feature in cluster AGN spectra using deep Chandra observations, finding mild statistical improvements that suggest possible but inconclusive evidence for such a feature.

Contribution

It provides a re-analysis of Chandra data focusing on the 3.5 keV spectral dip, contributing new insights into the ongoing search for dark matter signatures.

Findings

Mild spectral fit improvements at 3.5 keV in Perseus and Virgo clusters

Re-analysis of archival data confirms similar fit improvements

Results are suggestive but not definitive of a spectral dip at 3.5 keV

Abstract

We investigate possible evidence for a spectral dip around 3.5 keV in central cluster AGNs, motivated by previous results for archival Chandra observations of the Perseus cluster and the general interest in novel spectral features around 3.5 keV that may arise from dark matter physics. We use two deep Chandra observations of the Perseus and Virgo clusters that have recently been made public. In both cases, mild improvements in the fit ($\Delta \chi^2 = 4.2$ and $\Delta \chi^2 = 2.5$) are found by including such a dip at 3.5 keV into the spectrum. A comparable result ($\Delta \chi^2 = 6.5$) is found re-analysing archival on-axis Chandra ACIS-S observations of the centre of the Perseus cluster.