Constraints on dark matter annihilation in clusters of galaxies with the Fermi large area telescope

Abstract

Nearby clusters and groups of galaxies are potentially bright sources of high-energy gamma-ray emission resulting from the pair-annihilation of dark matter particles. However, no significant gamma-ray emission has been detected so far from clusters in the first 11 months of observations with the Fermi Large Area Telescope. We interpret this non-detection in terms of constraints on dark matter particle properties. In particular for leptonic annihilation final states and particle masses greater than ∼ 200 GeV, gamma-ray emission from inverse Compton scattering of CMB photons is expected to dominate the dark matter annihilation signal from clusters, and our gamma-ray limits exclude large regions of the parameter space that would give a good fit to the recent anomalous Pamela and Fermi-LAT electron-positron measurements. We also present constraints on the annihilation of more standard dark matter candidates, such as the lightest neutralino of supersymmetric models. The constraints are particularly strong when including the fact that clusters are known to contain substructure at least on galaxy scales, increasing the expected gamma-ray flux by a factor of ∼ 5 over a smooth-halo assumption. We also explore the effect of uncertainties in cluster dark matter density profiles, finding a systematic uncertainty in the constraints of roughly a factor of two, but similar overall conclusions. In this work, we focus on deriving limits on dark matter models; a more general consideration of the Fermi-LAT data on clusters and clusters as gamma-ray sources is forthcoming.

Indirect detection of dark matter with γ rays

“…In addition, these objects are expected to harbor a significant population of cosmic rays that should radiate γ rays through interaction with hadronic material and subsequent pion decay. As long as no signal is found, ignoring this contribution represents a conservative assumption and is therefore justified (36,(38)(39)(40)(41). Early claims of a signal in the Fermi-LAT data from the Virgo cluster (42) turned out to be due to several unmodeled point sources within the cluster (43) (45), and the H.E.S.S.…”

Components of the Extragalactic Gamma-Ray Background

“…The Fermi observations have placed significant constraints on extragalactic dark matter annihilation (Cirelli et al 2010;Abdo et al 2010a;Ackermann et al 2010a). Currently, there is no evidence of quark-annihilation features and spectral lines seen in the EGB spectrum, features that would be a clear annihilation signal (see, e.g., Stecker & Tylka 1989a;Rudaz & Stecker 1991).…”

“…The spectra of these potential contributions to the EGB differ considerably from that of the FSRQs (Silk & Srednicki 1984;Stecker et al 1985;Rudaz & Stecker 1988;Stecker & Tylka 1989a, 1989bRudaz & Stecker 1991;Ullio et al 2002;Ando et al 2007;Kalashev et al 2009;Siegal-Gaskins & Pavlidou 2009;Berezinsky et al 2011;Ahlers et al 2010;Venters 2010). However, recent Fermi observations have placed significant constraints on dark matter annihilation (Cirelli et al 2010;Abdo et al 2010a;Ackermann et al 2010a), and presently there is no clear evidence of annihilation features above the background continuum. As such, it appears that any putative contribution to the EGB from dark matter annihilation is relatively minor.…”

Constraining dark matter annihilation with the isotropicγ-ray background: Updated limits and future potential

“…[1] for a recent review). Unprecedented γ-ray observations of diffuse emission and point sources by the Fermi-LAT [2] have stimulated the search for exotic components from DM annihilation in the Milky Way, in extragalactic nearby objects, as well as in cosmological structures [3][4][5][6][7]. The incontrovertible DM signature would be a γ-ray monochromatic line at energies around the WIMP mass.…”