J1615+5452: a remnant radio galaxy in the ELAIS-N1 field

We report the discovery of a remnant radio AGN J1615+5452 in the field of ELAIS-N1. GMRT continuum observations at 150, 325 and 610 MHz combined with archival data from the 1.4 GHz NVSS survey were used to derive the radio spectrum of the source. At a redshift $z\sim$ 0.33, J1615+5452 has a linear size of $\sim$ 100 kpc and spectral indices ranging between ${\alpha }_{610}^{1400}<-1.5$ and ${\alpha }_{150}^{325}=-0.61\pm 0.12$. While the source has a diffuse radio emission at low frequencies, we do not find evidence of core, jets or hotspots in the 1.4,GHz VLA data of $\sim 5$ arcsec angular resolution. Such morphological properties coupled with a curved radio spectrum suggest that the AGN fueling mechanisms undergo a shortage of energy supply which is typical of a dying radio AGN. This is consistent with the observed steep curvature in the spectrum $\mathrm{\Delta }\alpha \approx -1$, the estimated synchrotron age of $t_{\mathrm{s}}=76.0_{-8.7}^{+7.4}$ Myr and a $t_{\rm off}/t_{\rm s}$ratioof$\sim 0.3$.