Search for line-like and box-shaped spectral features from nearby galaxy clusters with 11.4 years of Fermi LAT data

TL;DR

This study analyzed 11.4 years of Fermi LAT data from nearby galaxy clusters to search for gamma-ray spectral features indicative of dark matter, finding no significant signals but setting upper limits on annihilation cross sections.

Contribution

It provides the most comprehensive search for line-like and box-shaped gamma-ray features in galaxy clusters using extended Fermi LAT data, improving constraints on dark matter annihilation.

Findings

No statistically significant gamma-ray line detected.

Upper limits set on dark matter annihilation cross sections.

Hints at a spectral feature around 42 GeV are not statistically significant.

Abstract

Sharp spectral structures in the $\gamma$-ray band are an important dark matter (DM) signature. Previously, a tentative line feature at $\sim 43~{\rm GeV}$ is reported in 16 nearby galaxy clusters (GCls) with 7.1 years of Fermi-LAT data, whose TS value is $\sim 16.7$. In this work, we search for line signals and box-shaped structures using the stacked data from those 16 GCls with 11.4-yr P8R3 data. There is still a hint at $\sim {42~\rm GeV}$, dominated by the radiation of Virgo and Ophiuchus clusters. Though the TS value was high up to 21.2 in October 2016, currently it has dropped to 13.1. Moreover, the TS value at $\sim {42~\rm GeV}$ decreases to 2.4 when the EDISP2 data are excluded from the analysis. Consequently, we do not find any statistically significant line-like signal and then set up the 95% confidence level upper limits on the thermally averaged cross section of DM annihilating into double photons. The same line search has been carried out for an alternative GCl sample from the Two Micron All-Sky Survey but no any evidence has been found. We also search for box-shaped features in those 16 baseline GCls. No signal is found as well and the corresponding upper limits on the annihilation cross section are given.