The X-ray properties and structure of A3571 up to $R_{500}$

TL;DR

This study uses wide-field X-ray data to analyze the structure and properties of galaxy cluster A3571 beyond its core, revealing signs of past minor merger activity and demonstrating the capabilities of the EP-FXT instrument.

Contribution

It extends measurements of A3571's properties beyond R500 using EP-FXT data, identifying subtle dynamical features indicative of a recent minor merger.

Findings

Detection of surface-brightness excesses on both sides of the cluster

Lower temperature, pressure, and entropy in the northern excess region

No evidence of cold fronts or shocks, suggesting post-merger sloshing

Abstract

Abell 3571 is a nearby, X-ray bright galaxy cluster located in the Shapley Supercluster. Although it appears morphologically relaxed in X-ray images, multiwavelength observations reveal subtle indications of residual dynamical activity, likely associated with past merger events. Using wide-field ($1^{\circ} \times 1^{\circ}$) data from the Einstein Probe Follow-up X-ray Telescope (EP-FXT), we extend measurements of the cluster's properties beyond its $R_{500}$ radius. We detect surface-brightness excesses on both the northern and southern sides, consistent with previous XMM-Newton results. The temperature, pressure, and entropy in the northern excess region are lower than the average values, whereas those on the southern side are slightly higher. However, we find no evidence for cold fronts or shocks. These features can be interpreted as sloshing motions triggered by an off-center minor merger. Our findings suggest that, despite its symmetric appearance, A3571 is still recovering from a minor merger and is currently in a post-merger phase. This work also demonstrates the excellent capability of EP-FXT for probing the outskirts of galaxy clusters.