2017A&A...604A..21I

Context. We report on new Karl Jansky Very Large Array (JVLA) observations performed at 3GHz and 5.5GHz of Abell 2626. The cluster has been the object of several studies in recent years due to its peculiar radio emission, which shows a complex system of symmetric radio arcs characterized by a steep spectrum. The origin of these radio sources is still unclear. Due to their mirror symmetry toward the center, it has been proposed that they may be created by pairs of precessing jets powered by the inner active galactic nuclei (AGN).
Aims. The new JVLA observations were requested with the specific aim of detecting extended emission on frequencies higher than 1.4GHz, in order to constrain the jet-precession model by analyzing the spectral index and radiative age patterns along the arcs.
Methods. We performed a standard data reduction of the JVLA datasets with the software CASA. By combining the new 3GHz data with the archival 1.4GHz VLA dataset we produced a spectral index map of the extended emission, and then estimated the radiative age of the arcs by assuming that the plasma was accelerated in moving hot-spots tracing the arcs.
Results. Thanks to the high sensitivity of the JVLA, we achieve the detection of the arcs at 3GHz and extended emission at 5.5GHz. We measure a mean spectral index < -2.5 for the arcs up to 3GHz. No clear trend in spectral index or radiative age is detected across the arcs, which may challenge the interpretation based on precession or put strong constraints on the jet-precession period. In particular, by analyzing the radiative age distribution along the arcs, we were able to provide for the first time a timescale <26Myr of the jet-precession period.