Erratum: “Search for Gamma-Ray Emission from the Coma Cluster with Six Years of Fermi-LAT Data” (2016, ApJ, 819, 149)

Abstract

We present results from γ-ray observations of the Coma cluster incorporating 6 years of Fermi-LAT data and the newly released "Pass 8" event-level analysis. Our analysis of the region reveals low-significance residual structures within the virial radius of the cluster that are too faint for a detailed investigation with the current data. Using a likelihood approach that is free of assumptions on the spectral shape we derive upper limits on the γ-ray flux that is expected from energetic particle interactions in the cluster. We also consider a benchmark spatial and spectral template motivated by models in which the observed radio halo is mostly emission by secondary electrons. In this case, the median expected and observed upper limits for the flux above 100 MeV are 1.7 × 10 −9 ph cm −2 s −1 and 5.2 × 10 −9 ph cm −2 s −1 respectively (the latter corresponds to residual emission at the level of 1.8σ). These bounds are comparable to or higher than predicted levels of hadronic gamma-ray emission in cosmic-ray models with or without reacceleration of secondary electrons, although direct comparisons are sensitive to assumptions regarding the origin and propagation mode of cosmic rays and magnetic field properties. The minimal expected γ-ray flux from radio and star-forming galaxies within the Coma cluster is roughly an order of magnitude below the median sensitivity of our analysis.

Search for Dark Matter Annihilation in Galaxy Groups

“…An alternative to studying the full-sky imprint of extragalactic DM annihilation is to use individual galaxy clusters [21][22][23][24][25][26][27][28][29][30]. Previous analyses along these lines have looked at a small number of ∼10 14 -10 15 M X-rayselected clusters.…”

“…Using group catalogs to study gamma-ray emission from cosmic rays in these objects is an interesting study in its own right (see, e.g., Ref. [24,26,48,49]), which we leave to future work. For the purpose of the present analysis, however, we would like a way to remove groups with large residuals, likely arising from standard astrophysical processes in the clusters, to maintain maximum sensitivity to DM annihilation.…”

Cross-correlation of the extragalactic gamma-ray background with the thermal Sunyaev-Zel’dovich effect in the cosmic microwave background

“…On the other hand, the cross-correlation at smaller scales (l ∼ 1000) can probe the gamma rays in galaxy clusters at z ∼ 0.1-0.2. Since most gamma-ray studies of galaxy clusters concentrate on objects at z ≲ 0.1 [11][12][13]52,53], the cross-correlation analysis with the UGRB intensity and the tSZ Compton parameter is a comprehensive approach to study gamma rays in the ICM at higher redshifts.…”

“…We vary the amplitude of the mass-dependent term in the gamma-ray profiles [Eq. (13) different parameters in modeling the tSZ-UGRB power spectrum and compare with our fiducial model. We find that the dependence of our modeling on the shape of pressure profile is small.…”

“…The detection of gamma-ray emission produced by the decay of secondary π 0 particles is the most direct probe of cosmicray protons in galaxy clusters. Despite intense efforts in gamma-ray astronomy, no conclusive evidence for gamma-ray emission in the ICM has been reported so far [5][6][7][8][9][10][11][12][13][14] (but see Ref. [15] for the recent update).…”