The structure of cluster merger shocks: turbulent width and the electron heating timescale

Abstract

We present a new 2 Ms Chandra observation of the cluster merger Abell 2146, which hosts two huge M~2 shock fronts each ~500 kpc across. For the first time, we resolve and measure the width of cluster merger shocks. The best-fit width for the bow shock is 17+/-1 kpc and for the upstream shock is 10.7+/-0.3 kpc. A narrow collisionless shock will appear broader in projection if its smooth shape is warped by local gas motions. We show that both shock widths are consistent with collisionless shocks blurred by local gas motions of 290+/-30 km/s. The upstream shock forms later on in the merger than the bow shock and is therefore expected to be significantly narrower. From the electron temperature profile behind the bow shock, we measure the timescale for the electrons and ions to come back into thermal equilibrium. We rule out rapid thermal equilibration of the electrons with the shock-heated ions at the 6 sigma level. The observed temperature profile instead favours collisional equilibration. For these cluster merger shocks, which have low sonic Mach numbers and propagate through a high $\beta$ plasma, we find no evidence for electron heating over that produced by adiabatic compression. Our findings are expected to be valid for collisionless shocks with similar parameters in other environments and support the existing picture from the solar wind and supernova remnants. The upstream shock is consistent with this result but has a more complex structure, including a ~2 keV increase in temperature ~50 kpc ahead of the shock.

arXiv comment18 pages, 17 figures, 1 table, accepted to MNRAS

References in corpus (43)

• The Leiden/Argentine/Bonn (LAB) Survey of Galactic HI: Final data release of the combined LDS and IAR surveys with improved stray-radiation corrections
• A direct empirical proof of the existence of dark matter
• Collisional Plasma Models with APEC/APED: Emission Line Diagnostics of Hydrogen-like and Helium-like Ions
• Shocks and cold fronts in galaxy clusters
• The Northern ROSAT All-Sky (NORAS) Galaxy Cluster Survey I: X-ray Properties of Clusters Detected as Extended X-ray Sources
• Simulations of Ion Acceleration at Non-relativistic Shocks. I. Acceleration Efficiency
• Chandra temperature profiles for a sample of nearby relaxed galaxy clusters
• The Quiescent Intracluster Medium in the Core of the Perseus Cluster
• Diffuse Radio Emission from Galaxy Clusters
• Bow shock and radio halo in the merging cluster A520
• The microphysics of collisionless shock waves
• A deeper X-ray study of the core of the Perseus galaxy cluster: the power of sound waves and the distribution of metals and cosmic rays
• Simultaneous Acceleration of Protons and Electrons at Nonrelativistic Quasiparallel Collisionless Shocks
• Contour binning: a new technique for spatially-resolved X-ray spectroscopy applied to Cassiopeia A
• Simulations of Ion Acceleration at Non-relativistic Shocks. II. Magnetic Field Amplification
• Non-Thermal Electron Acceleration in Low Mach Number Collisionless Shocks. I. Particle Energy Spectra and Acceleration Mechanism
• Simulations and Theory of Ion Injection at Non-relativistic Collisionless Shocks
• Electron-Ion Temperature Equilibration in Collisionless Shocks: the Supernova Remnant-Solar Wind Connection
• Chandra observation of two shock fronts in the merging galaxy cluster Abell 2146
• Shock fronts, electron-ion equilibration and ICM transport processes in the merging cluster Abell 2146
• Direct X-ray Spectral Deprojection of Galaxy Clusters
• Electron acceleration in non-relativistic quasi-perpendicular collisionless shocks
• Electron energy partition across interplanetary shocks: I. Methodology and Data Product
• Hydrodynamic Simulations of Merging Galaxy Clusters: Non-Equilibrium Ionization State and Two-Temperature Structure
• Electron energy partition across interplanetary shocks: II. Statistics
• Proton Acceleration in Weak Quasi-parallel Intracluster Shocks: Injection and Early Acceleration
• Effects of the Non-Equipartition of Electrons and Ions in the Outskirts of Relaxed Galaxy Clusters
• Constraints on turbulent velocity broadening for a sample of clusters, groups and elliptical galaxies using XMM-Newton
• Electron Heating in Low Mach Number Perpendicular shocks. I. Heating Mechanism
• Deep Chandra Observations of Abell 2199: the Interplay between Merger-Induced Gas Motions and Nuclear Outbursts in a Cool Core Cluster
• Electron Heating in Low Mach Number Perpendicular shocks. II. Dependence on the Pre-Shock Conditions
• Arithmetic with X-ray images of galaxy clusters: effective equation of state for small-scale perturbations in the ICM
• Standoff Distance of Bow Shocks in Galaxy Clusters as Proxy for Mach Number
• An ALMA+ACA measurement of the shock in the Bullet Cluster
• Electron energy partition across interplanetary shocks: III. Analysis
• Kinetic simulation of nonrelativistic perpendicular shocks of young supernova remnants. IV. Electron heating
• Bow shock in merging cluster A520: the edge of the radio halo and the electron-ion equilibration timescale
• Dynamical analysis of galaxy cluster merger Abell 2146
• The X-ray coronae of the two brightest galaxies in the Coma cluster
• Riding the wake of a merging galaxy cluster
• The Distribution of Dark and Luminous Matter in the Unique Galaxy Cluster Merger Abell 2146
• Non-Equilibrium Ionization State and Two-Temperature Structure in the Bullet Cluster 1E0657-56
• X-ray Signatures of Non-Equilibrium Ionization Effects in Galaxy Cluster Accretion Shock Regions