Search for Line-like and Box-shaped Spectral Features from Nearby Galaxy Clusters with 11.4 Years of Fermi Large Area Telescope Data

Abstract

Sharp spectral structures in the γ-ray band are an important dark matter (DM) signature. Previously, a tentative line feature at ∼43 GeV was reported in 16 nearby galaxy clusters (GCls) with 7.1 yr of Fermi Large Area Telescope (LAT) data, whose test statistic (TS) value is ∼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 of Fermi-LAT P8R3 data. There is still a hint at ∼42 GeV, dominated by the radiation of the Virgo and Ophiuchus clusters. Though the TS value was high up to 21.2 in 2016 October, currently it has dropped to 13.1. Moreover, the TS value at ∼42 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 evidence has been found. We also search for box-shaped features in those 16 baseline GCls. No signal is found, and the corresponding upper limits on the annihilation cross section are given.

Search for gamma-ray spectral lines with the DArk Matter Particle Explorer

“…The potential ∼ 133 GeV line reported in the Galactic center [18,19,21] was recognized as a systematic effect later [26]. The tentative signature at ∼ 43 GeV from a nearby Galaxy cluster sample [28] is found to have a strange temporal behavior of its significance [33]. Nevertheless, the γ-ray line signal is so important that independent line searches with data from different telescopes are needed.…”

“…Though plentiful works have been carried out to search for γ-ray lines after the launch of Fermi Gamma-ray Space Telescope, no GeV line signal has been formally detected yet [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33]. The potential ∼ 133 GeV line reported in the Galactic center [18,19,21] was recognized as a systematic effect later [26].…”