Cosmological Magnetohydrodynamic Simulations of Galaxy Cluster Radio Relics: Insights and Warnings for Observations

Skillman, Samuel W.; Xu, Hao; Hallman, Eric J.; O’Shea, Brian W.; Burns, Jack O.; Li, Hui; Collins, David C.; Norman, Michael L.

doi:10.1088/0004-637x/765/1/21

Cited by 124 publications

(172 citation statements)

References 89 publications

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“…On the other hand, X-ray observations with Suzaku derived a Mach number ∼ 3 from the temperature jump at the relic, 307 which would imply α in j 0.75. In this respect it is worth mentioning that numerical simulations show variations of the Mach number over shocks 315 that potentially might produce some differences in the shock Mach numbers derived from X-rays (temperature or density jumps) and from radio. In this case the radio Mach number would be biased high because synchrotron emission is likely to be locally stronger in regions with higher Mach number.…”

Section: Open Problems and Particle Re-acceleration At Shocksmentioning

confidence: 99%

Cosmic Rays in Galaxy Clusters and Their Nonthermal Emission

Brunetti¹,

Jones

2014

Int. J. Mod. Phys. D

595

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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Section: Open Problems and Particle Re-acceleration At Shocksmentioning

confidence: 99%

Cosmic Rays in Galaxy Clusters and Their Nonthermal Emission

Brunetti¹,

Jones

2014

Int. J. Mod. Phys. D

595

732

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“…Shocks tracing radio relics should consist of a mixture of Mach numbers along the line of sight, as hydrodynamical simulations indicate (e.g., Skillman et al 2011Skillman et al , 2013Vazza et al 2012). If the acceleration efficiency is a nonlinear function of the Mach number (e.g., Hoeft & Brüggen 2007), the synchrotron-weighted Mach number would naturally be higher than the X-ray weighted Mach number.…”

Section: A Mixture Of Mach Numbersmentioning

confidence: 99%

Lofar, Vla, and Chandra Observations of the Toothbrush Galaxy Cluster

Weeren

Brunetti

Brüggen

et al. 2016

ApJ

154

212

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We present deep LOFAR observations between 120 and 181 MHz of the "Toothbrush" (RX J0603.3+4214), a cluster that contains one of the brightest radio relic sources known. Our LOFAR observations exploit a new and novel calibration scheme to probe 10 times deeper than any previous study in this relatively unexplored part of the spectrum. The LOFAR observations, when combined with VLA, GMRT, and Chandra X-ray data, provide new information about the nature of cluster merger shocks and their role in re-accelerating relativistic particles. We derive a spectral index of 0.8 0.1 a = - at the northern edge of the main radio relic, steepening toward the south to 2 a » -. The spectral index of the radio halo is remarkably uniform ( 1.16 a = -, with an intrinsic scatter of 0.04  ). The observed radio relic spectral index gives a Mach number of 2.8 0.3 0.5  = -+ , assuming diffusive shock acceleration. However, the gas density jump at the northern edge of the large radio relic implies a much weaker shock ( 1.2  » , with an upper limit of 1.5  » ). The discrepancy between the Mach numbers calculated from the radio and X-rays can be explained if either (i) the relic traces a complex shock surface along the line of sight, or (ii) if the radio relic emission is produced by a re-accelerated population of fossil particles from a radio galaxy. Our results highlight the need for additional theoretical work and numerical simulations of particle acceleration and reacceleration at cluster merger shocks.

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“…Using the measured integrated spectral index and an assumption for the cooling effect, a similar trend has been seen in several radio relics and edges of the halo (Markevitch et al 2005;). There are several mechanism proposed to explain the particle acceleration in clusters (Markevitch et al 2005;Kang et al 2012;Pinzke et al 2013;Skillman et al 2013). A plausible possibility is re-acceleration of pre-existing nonthermal (low-energy cosmic-ray) particles in the ICM.…”

Section: Mach Number From X-ray and Radio Observationsmentioning

confidence: 99%

SuzakuX-ray study of the double radio relic galaxy cluster CIZA J2242.8+5301

Akamatsu

Weeren

Ogrean

et al. 2015

A&A

105

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Context. We present the results from Suzaku observations of the merging cluster of galaxies CIZA J2242.8+5301 at z = 0.192. Aims. To study the physics of gas heating and particle acceleration in cluster mergers, we investigated the X-ray emission from CIZA J2242.8+5301, which hosts two giant radio relics in the northern and southern part of the cluster. Methods. We analyzed data from three-pointed Suzaku observations of CIZA J2242.8+5301 to derive the temperature distribution in four different directions. Results. The intracluster medium (ICM) temperature shows a remarkable drop from 8.5 +0.8 −0.6 keV to 2.7 +0.7 −0.4 keV across the northern radio relic. The temperature drop is consistent with a Mach number M n = 2.7 +0.7 −0.4 and a shock velocity v shock:n = 2300 +700 −400 km s −1 . We also confirm the temperature drop across the southern radio relic. However, the ICM temperature beyond this relic is much higher than beyond the northern relic, which gives a Mach number M s = 1.7 +0.4 −0.3 and shock velocity v shock:s = 2040 +550 −410 km s −1 . These results agree with other systems showing a relationship between the radio relics and shock fronts which are induced by merging activity. We compare the X-ray derived Mach numbers with the radio derived Mach numbers from the radio spectral index under the assumption of diffusive shock acceleration in the linear test particle regime. For the northern radio relic, the Mach numbers derived from X-ray and radio observations agree with each other. Based on the shock velocities, we estimate that CIZA J2242.8+5301 is observed approximately 0.6 Gyr after core passage. The magnetic field pressure at the northern relic is estimated to be 9% of the thermal pressure.

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Cosmological Magnetohydrodynamic Simulations of Galaxy Cluster Radio Relics: Insights and Warnings for Observations

Cited by 124 publications

References 89 publications

Cosmic Rays in Galaxy Clusters and Their Nonthermal Emission

Cosmic Rays in Galaxy Clusters and Their Nonthermal Emission

Lofar, Vla, and Chandra Observations of the Toothbrush Galaxy Cluster

SuzakuX-ray study of the double radio relic galaxy cluster CIZA J2242.8+5301

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