Multiwavelength study of radio galaxy Pictor A: detection of western hotspot in far-UV and possible origin of high energy emissions

Abstract

A comprehensive study of the nucleus and western hotspot of Pictor A is carried out using AstroSat observations, 13 yr of Fermi, and archival Swift observations along with other published data. We report the first detection of the western hotspot of Pictor A in the far-UV band using observations from AstroSat-UVIT. The broad-band SED of the western hotspot is explained by a multizone emission scenario, where X-ray emission is caused by synchrotron emission process in the substructures embedded in the diffuse region, while the emission in radio to optical is caused by synchrotron emission process in the diffuse region. We do not notice any excess in the IR band and an additional zone (beyond 2-zone) is not required to account for the X-ray emission. Our broad-band spectro-temporal study and associated modelling of the core and hotspot of Pictor A suggests that (a) γ -rays originate in the nuclear jet and not from the hotspot (b) X-ray emission from the core of Pictor A has nuclear jet-origin instead of previously reported disc-origin.