The puzzling radio source in the cool core cluster A 2626

TL;DR

This study presents new high-resolution radio observations of the cool core cluster A 2626, revealing complex arc structures and confirming diffuse mini-halo emission, challenging typical jet-lobe models.

Contribution

The paper provides the first detailed imaging of unusual radio arcs and confirms the presence of a diffuse mini-halo in A 2626 with unprecedented sensitivity.

Findings

Discovery of bright radio arcs with steep spectra

Detection of a diffuse radio mini-halo

Identification of complex radio morphology in A 2626

Abstract

We report on new VLA radio observations performed at 1.4 GHz and 4.8 GHz with unprecedented sensitivity and angular resolution (~1 arcsec) of the cool core cluster A 2626, which is known to possess a radio mini-halo at its center. The most unusual features of A 2626 are two elongated radio features detected in previous observations to the north and south, having morphologies not common to the typical jet-lobe structures in cool cores. In our new sensitive images the two elongated features appears clearly as bright radio arcs, and we discover the presence of a new arc to the west. These radio arcs are not detected at 4.8 GHz, implying a steep (alpha >1) spectrum, and their origin is puzzling. After subtracting the flux density contributed by these discrete features from the total flux measured at low resolution, we estimate a residual 18.0 +/- 1.8 mJy flux density of diffuse radio emission at 1.4 GHz. We therefore confirm the detection of diffuse radio emission, which appears distinct from the discrete radio arcs embedded in it. Although its radio power is lower (1.4x10^23 W/Hz) than previously known, the diffuse emission may still be classified as a radio mini-halo.