Megaparsec-scale Radio Structure Associated with a Hybrid Blazar SBS B1646+499: Episodic Jet Activity with Precessing Axis

Abstract

Abstract Here we report on the total-intensity 610 MHz Giant Meterwave Radio Telescope (GMRT) observations of the peculiar hybrid blazar SBS B1646+499, which merges the properties of BL Lacertae objects and flat-spectrum radio quasars. The complex radio structure of SBS B1646+499, emerging from the archival radio data and our new GMRT observations, consists of the megaparsec-scale elongated halo, the unilateral kiloparsec-scale jet, and the nuclear jet extending up to ∼20 pc from the compact core. The giant halo is characterized by a steep radio spectrum, indicative of the advanced aging of the electron population within the lobes. For the large-scale jet, we detected a spectral gradient along and across the outflow, and in particular spectral flattening of the radio continuum toward the jet edges, suggestive of the spine-boundary shear layer morphology. The nuclear jet displays superluminal knots emerging from the self-absorbed and variable radio core. We interpret all these findings in the framework of the model of an episodic jet activity with a precessing jet axis.