The X-ray properties and structure of A3571 up to R₅₀₀

¹ School of Physics and Astronomy, Beijing Normal University Beijing 100875, China
² State Key Laboratory of Particle Astrophysics, Institute of High Energy Physics, Chinese Academy of Sciences Beijing 100049, China
³ Max Planck Institute for Extraterrestrial Physics Giessenbachstrasse 1 85748 Garching, Germany
⁴ Institute for Frontiers in Astronomy and Astrophysics, Beijing Normal University Beijing 102206, China
⁵ National Astronomical Observatories, Chinese Academy of Sciences 20A Datun Road Beijing 100101, China
⁶ Department of Astronomy, Xiamen University Xiamen 361005, China
⁷ School of Astronomy and Space Science, University of Chinese Academy of Sciences 19A Yuquan Road Beijing 100049, China

^★ Corresponding authors: This email address is being protected from spambots. You need JavaScript enabled to view it. ; This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 14 October 2025
Accepted: 26 January 2026

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° ×1°) data from the Einstein Probe Follow-up X-ray Telescope (EP-FXT), we extended measurements of the cluster’s properties beyond its R₅₀₀ 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 of 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.