Counting gamma rays in the directions of galaxy clusters

Prokhorov, Dmitry; Churazov, E.

doi:10.1051/0004-6361/201322454

Cited by 50 publications

(65 citation statements)

References 53 publications

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“…An analysis of 50 clusters using four years of data from the Large Area Telescope (LAT) on board the Fermi satellite (Ackermann et al 2014a) resulted in upper limits on the CRinduced γ-ray emission (see also Ackermann et al 2010;Huber et al 2013;Griffin et al 2014;Prokhorov & Churazov 2014). The γ-ray upper limits from these analyses put stringent constraints on the energy density of energetic protons in clusters, severely constraining models for acceleration by structure formation shocks (reviewed by Brunetti & Jones 2014).…”

Section: Introductionmentioning

confidence: 99%

Search for Gamma-Ray Emission From the Coma Cluster With Six Years of Fermi-Lat Data

Ackermann¹,

Ajello²,

Albert³

et al. 2016

ApJ

108

118

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We present results from γ-ray observations of the Coma cluster incorporating six 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 (CR) models with or without reacceleration of secondary electrons, although direct comparisons are sensitive to assumptions regarding the origin and propagation mode of CRs 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.

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Section: Introductionmentioning

confidence: 99%

Search for Gamma-Ray Emission From the Coma Cluster With Six Years of Fermi-Lat Data

Ackermann¹,

Ajello²,

Albert³

et al. 2016

ApJ

108

118

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“…Only upper limits to the γ-ray emission have been obtained for both individual nearby clusters and from the stacking of samples of clusters. 30,32,33,[199][200][201] Under the assumption that the spatial distribution of CRp roughly follows that of the thermal ICM, in the most stringent cases (including stacking procedures) these limits constrain E CR /E ICM < about 1% (Fig. 10), with only a weak dependence on δ .…”

Section: Limits On Crpmentioning

confidence: 99%

Cosmic Rays in Galaxy Clusters and Their Nonthermal Emission

Brunetti¹,

Jones

2014

Int. J. Mod. Phys. D

625

732

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Radio observations prove the existence of relativistic particles and magnetic field associated with the intra-cluster-medium (ICM) through the presence of extended synchrotron emission in the form of radio halos and peripheral relics. This observational evidence has fundamental implications on the physics of the ICM. Non-thermal components in galaxy clusters are indeed unique probes of very energetic processes operating within clusters that drain gravitational and electromagnetic energy into cosmic rays and magnetic fields. These components strongly affect the (micro-)physical properties of the ICM, including viscosity and electrical conductivities, and have also potential consequences on the evolution of clusters themselves. The nature and properties of cosmic rays in galaxy clusters, including the origin of the observed radio emission on cluster-scales, have triggered an active theoretical debate in the last decade. Only recently we can start addressing some of the most important questions in this field, thanks to recent observational advances, both in the radio and at high energies. The properties of cosmic rays and of cluster non-thermal emissions depend on the dynamical state of the ICM, the efficiency of particle acceleration mechanisms in the ICM and on the dynamics of these cosmic rays. In this review we discuss in some detail the acceleration and transport of cosmic rays in galaxy clusters and the most relevant observational milestones that have provided important steps on our understanding of this physics. Finally, looking forward to the possibilities from new generations of observational tools, we focus on what appear to be the most important prospects for the near future from radio and high-energy observations.

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“…In each panel, the vertical dashed lines indicate the characteristic CRe energies corresponding to the frequencies of 327 and 1420 MHz. emission from neutral pions, which are produced in the same hadronic interactions and subsequently decay (Ackermann et al 2010;MAGIC Collaboration et al 2011;The Fermi-LAT Collaboration et al 2013;Prokhorov & Churazov 2013).…”

Section: Modeling the Crpmentioning

confidence: 99%

“…These hadronic interactions should also produce a flux of γ-rays, but so far no confirmed detections of such emission from galaxy clusters have been made. Upper limits on the γ-ray flux from several experiments (see, e.g., MAGIC Collaboration et al 2011;The Fermi-LAT Collaboration et al 2013;Prokhorov & Churazov 2013) indicate the ratio of the CRp energy to the thermal energy of the gas is at most ∼1-2%. Still, contrary to the case of nearby giant radio halos, these limits do not put significant tension on a secondary origin of mini-halos (Brunetti & Jones 2014).…”

Section: Introductionmentioning

confidence: 99%

Testing Secondary Models for the Origin of Radio Mini-Halos in Galaxy Clusters

ZuHone

Brunetti

Giacintucci

et al. 2015

ApJ

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We present an MHD simulation of the emergence of a radio minihalo in a galaxy cluster core in a "secondary" model, where the source of the synchrotron-emitting electrons is hadronic interactions between cosmic-ray protons with the thermal intracluster gas, an alternative to the "reacceleration model" where the cosmic ray electrons are reaccelerated by turbulence induced by core sloshing, which we discussed in an earlier work. We follow the evolution of cosmic-ray electron spectra and their radio emission using passive tracer particles, taking into account the time-dependent injection of electrons from hadronic interactions and their energy losses. We find that secondary electrons in a sloshing cluster core can generate diffuse synchrotron emission with luminosity and extent similar to observed radio minihalos. However, we also find important differences with our previous work. We find that the drop in radio emission at cold fronts is less prominent than that in our reacceleration-based simulations, indicating that in this flavor of the secondary model the emission is more spatially extended than in some observed minihalos. We also explore the effect of rapid changes in the magnetic field on the radio spectrum. While the resulting spectra in some regions are steeper than expected from stationary conditions, the change is marginal, with differences in the synchrotron spectral index of  a D 0.15-0.25, depending on the frequency band. This is a much narrower range than claimed in the best-observed minihalos and produced in the reacceleration model. Our results provide important suggestions to constrain these models with future observations.

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Counting gamma rays in the directions of galaxy clusters

Cited by 50 publications

References 53 publications

Search for Gamma-Ray Emission From the Coma Cluster With Six Years of Fermi-Lat Data

Search for Gamma-Ray Emission From the Coma Cluster With Six Years of Fermi-Lat Data

Cosmic Rays in Galaxy Clusters and Their Nonthermal Emission

Testing Secondary Models for the Origin of Radio Mini-Halos in Galaxy Clusters

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