Multiwavelength monitoring of the nucleus in PBC J2333.9−2343: the giant radio galaxy with a blazar-like core

Abstract

ABSTRACT PBC J2333.9−2343 is a giant radio galaxy at z  = 0.047 with a bright central core associated to a blazar nucleus. If the nuclear blazar jet is a new phase of the jet activity, then the small orientation angle suggests a dramatic change of the jet direction. We present observations obtained between 2018 September and 2019 January (cadence larger than three days) with Effeslberg, SMARTS-1.3m, ZTF, ATLAS, Swift, and Fermi-LAT, and between 2019 April and 2019 July (daily cadence) with SMARTS-1.3 m and ATLAS. Large (>2 ×) flux increases are observed on time-scales shorter than a month, which are interpreted as flaring events. The cross correlation between the SMARTS-1.3 m monitoring in the NIR and optical shows that these data do not show significant time lag within the measured errors. A comparison of the optical variability properties between non-blazars and blazars AGN shows that PBC J2333.9−2343 has properties more comparable to the latter. The SED of the nucleus shows two peaks, that were fitted with a one-zone leptonic model. Our data and modelling show that the high energy peak is dominated by External Compton from the dusty torus with mild contribution from Inverse Compton from the jet. The derived jet angle of 3 deg is also typical of a blazar. Therefore, we confirm the presence of a blazar-like core in the centre of this giant radio galaxy, likely a Flat Spectrum Radio Quasar with peculiar properties.