Emma Storm

Constraints on Dark Matter Annihilation in Clusters of Galaxies from Diffuse Radio Emission

Annihilation of dark matter can result in the production of stable Standard Model particles including electrons and positrons that, in the presence of magnetic fields, lose energy via synchrotron radiation, observable as radio emission. Galaxy clusters are excellent targets to search for or to constrain the rate of dark matter annihilation, as they are both massive and dark matter dominated. In this study, we place limits on dark matter annihilation in a sample of nearby clusters using upper limits on the diffuse radio emission, low levels of observed diffuse emission, or detections of radio mini-halos. We find that the strongest limits on the annihilation cross section are better than limits derived from the non-detection of clusters in the gamma-ray band by a factor of ~3 or more when the same annihilation channel and substructure model, but different best-case clusters, are compared. The limits on the cross section depend on the assumed amount of substructure, varying by as much as two orders of magnitude for increasingly optimistic substructure models as compared to a smooth Navarro-Frenk-White profile. In our most optimistic case, using the results of the Phoenix Project, we find that the derived limits reach below the thermal relic cross section of 3 ? 10?26?cm3 s?1 for dark matter masses as large as 400 GeV, for the annihilation channel. We discuss uncertainties due to the limited available data on the magnetic field structure of individual clusters. We also report the discovery of diffuse radio emission from the central 30-40?kpc regions of the groups M49 and NGC?4636.

A radio and X-ray study of the merging cluster A2319

A2319 is a massive, merging galaxy cluster with a previously detected radio halo that roughly follows the X-ray emitting gas. We present the results from recent observations of A2319 at 20 cm with the Jansky Very Large Array (VLA) and a re-analysis of the X-ray observations from XMM-Newton, to investigate the interactions between the thermal and nonthermal components of the ICM . We confirm previous reports of an X-ray cold front, and report on the discovery of a distinct core to the radio halo, 800 kpc in extent, that is strikingly similar in morphology to the X-ray emission, and drops sharply in brightness at the cold front. We detect additional radio emission trailing off from the core, which blends smoothly into the 2 Mpc halo detected with the Green Bank Telescope (GBT; Farnsworth et al., 2013). We speculate on the possible mechanisms for such a two-component radio halo, with sloshing playing a dominant role in the core. By directly comparing the X-ray and radio emission, we find that a hadronic origin for the cosmic ray electrons responsible for the radio halo would require a magnetic field and/or cosmic ray proton distribution that increases with radial distance from the cluster center, and is therefore disfavored.

Synchrotron Emission from Dark Matter Annihilation: Predictions for Constraints from Non-detections of Galaxy Clusters with New Radio Surveys

The annihilation of dark matter particles is expected to yield a broad radiation spectrum via the production of Standard Model particles in astrophysical environments. In particular, electrons and positrons from dark matter annihilation produce synchrotron radiation in the presence of magnetic fields. Galaxy clusters are the most massive collapsed structures in the universe, and are known to host

SkyFACT: High-dimensional modeling of gamma-ray emission with adaptive templates and penalized likelihoods

\sim\mu

GAMMA RAYS FROM STAR FORMATION IN CLUSTERS OF GALAXIES

G-scale magnetic fields. They are therefore ideal targets to search for, or to constrain the synchrotron signal from dark matter annihilation. In this work we use the expected sensitivities of several planned surveys from the next generation of radio telescopes to predict the constraints on dark matter annihilation models which will be achieved in the case of non-detections of diffuse radio emission from galaxy clusters. Specifically, we consider the Tier 1 survey planned for the Low Frequency Array (LOFAR) at 120 MHz, the EMU survey planned for the Australian Square Kilometre Array Pathfinder (ASKAP) at 1.4 GHz, and planned surveys for APERTIF at 1.4 GHz. We find that, for massive clusters and dark matter masses

Multiwavelength analysis of dark matter annihilation and RX-DMFIT

\lesssim 100

The Fermi-LAT GeV excess as a tracer of stellar mass in the Galactic bulge

GeV, the predicted limits on the annihilation cross section would rule out vanilla thermal relic models for even the shallow LOFAR Tier 1, ASKAP, and APERTIF surveys.

XMM-Newton Observations of the Southeastern Radio Relic in Abell 3667

We present SkyFACT (Sky Factorization with Adaptive Constrained Templates), anew approach for studying, modeling and decomposing diffuse gamma-ray emission.Like most previous analyses, the approach relies on predictions from cosmic-raypropagation codes like GALPROP and DRAGON. However, in contrast to previousapproaches, we account for the fact that models are not perfect and allow for avery large number (

On the progressive hardening of the cosmic-ray proton spectrum in the inner Galaxy

\gtrsim10^5

Understanding uncertainties in modeling the galactic diffuse gamma-ray emission

) of nuisance parameters to parameterize theseimperfections. We combine methods of image reconstruction and adaptivespatio-spectral template regression in one coherent hybrid approach. To thisend, we use penalized Poisson likelihood regression, with regularizationfunctions that are motivated by the maximum entropy method. We introducemethods to efficiently handle the high dimensionality of the convexoptimization problem as well as the associated semi-sparse covariance matrix,using the L-BFGS-B algorithm and Cholesky factorization. We test the methodboth on synthetic data as well as on gamma-ray emission from the inner Galaxy,