Chandra Observations of the Spectacular A3411-12 Merger Event

TL;DR

This paper presents detailed Chandra X-ray observations of the merging galaxy cluster A3411-12, providing evidence for electron re-acceleration at cluster shocks and characterizing the merger's properties.

Contribution

It offers the first detailed analysis of electron re-acceleration in A3411-12, combining X-ray data with shock and merger diagnostics to understand particle acceleration.

Findings

Small Mach number of the merger ($M \,\leq\, 1.15$)

Cluster undergoing a mild merger with extended radio relics

Presence of pre-existing energetic electrons in the cluster

Abstract

We present deep Chandra observations of A3411-12, a remarkable merging cluster that hosts the most compelling evidence for electron re-acceleration at cluster shocks to date. Using the $Y_X-M$ scaling relation, we find $r_{500} \sim 1.3$ Mpc, $M_{500} = (7.1 \pm 0.7) \times 10^{14} \ M_{\rm{\odot}}$, $kT=6.5\pm 0.1$ keV, and a gas mass of $M_{\rm g,500} = (9.7 \pm 0.1) \times 10^{13} M_\odot$. The gas mass fraction within $r_{500}$ is $f_{\rm g} = 0.14 \pm 0.01$. We compute the shock strength using density jumps to conclude that the Mach number of the merging subcluster is small ($M \leq 1.15_{-0.09}^{+0.14}$). We also present pseudo-density, projected temperature, pseudo-pressure, and pseudo-entropy maps. Based on the pseudo-entropy map we conclude that the cluster is undergoing a mild merger, consistent with the small Mach number. On the other hand, radio relics extend over Mpc scale in the A3411-12 system, which strongly suggests that a population of energetic electrons already existed over extended regions of the cluster.