GMRT unveils steep-spectrum antique filaments in the galaxy cluster
  Abell 725
  We present original GMRT radio observations of the galaxy cluster Abell~725,
at a redshift of 0.09, along with other archival observations. Our GMRT maps
reveal two steep-spectrum diffuse filaments in the cluster, along with a
previously reported arc-like structure, and a wide-angle tail (WAT) radio
source associated with the Brightest Cluster Galaxy (BCG) at the periphery of
the cluster. The bent morphology of the WAT indicates that its jets have been
swept back by the dynamic pressure resulting from the motion of the BCG through
the surrounding intracluster medium. The BCG associated with the WAT hosts a
black hole whose mass we estimate to be 1.4$\pm0.4 \times10^{9} \Msun$. We
observe a 2\arcmin (195\,kpc in projection) offset between the BCG and the
X-ray centroid of the galaxy cluster, which, along with other dynamic features,
indicates the cluster's early stage of evolution. The WAT radio galaxy, the arc
and the filaments have spectral indices $\alpha_{612}^{240}= -0.46\pm 0.15$,
$-0.8\pm0.3$, and ($-1.13\pm 0.48$, $-1.40\pm 0.50$), respectively. The WAT and
the arc are connected structures, while the filaments are detached from them,
but are found to be along the trail of the WAT. Based on the morphology of the
components, and the progressive steepening of the components from the core of
the WAT to the filaments, we propose that this system is a radio galaxy with
trailing antique filaments.
