A Strong Merger Shock in Abell 665

TL;DR

Deep Chandra observations of Abell 665 reveal a strong merger shock with Mach number 3, providing insights into shock dynamics and particle acceleration in galaxy clusters.

Contribution

First detection of a strong merger shock with Mach number around 3 in Abell 665, expanding understanding of shock phenomena in galaxy cluster mergers.

Findings

Detected a shock with Mach number 3 in Abell 665

Identified a southern cold front with heated gas

Observed potential radio emission extending to the shock

Abstract

Deep (103 ks) \chandra\ observations of Abell 665 have revealed rich structures in this merging galaxy cluster, including a strong shock and two cold fronts. The newly discovered shock has a Mach number of $M$ = 3.0 $\pm$ 0.6, propagating in front of a cold disrupted cloud. This makes Abell~665 the second cluster where a strong merger shock of $M \approx$ 3 has been detected, after the Bullet cluster. The shock velocity from jump conditions is consistent with (2.7 $\pm$ 0.7) $\times$ 10$^3$ km sec$^{-1}$. The new data also reveal a prominent southern cold front, with potentially heated gas ahead of it. Abell 665 also hosts a giant radio halo. There is a hint of diffuse radio emission extending to the shock at the north, which needs to be examined with better radio data. This new strong shock provides a great opportunity to study the re-acceleration model with the X-ray and radio data combined.