Imaging Results from the uGMRT Real-time Broadband RFI Excision System

Abstract

Radio halos and relics in clusters of galaxies are low brightness $( \sim \mu$ Jy arcsec $^{-2}$ at 1.4 GHz) extended sources and are direct probes of relativistic electrons and magnetic fields on mega-parsec scales. Low-frequency $(\lt$ GHz) radio observations with the Upgraded Giant Metrewave Radio Telescope (uGMRT) are most appropriate for studying these sources [e. g. 1]. One of the most important challenges with the uGMRT is the corruption of astronomical data due to man made broadband radio frequency interference (RFI). The effect of RFI is more pronounced on the shorter baselines which are critical for studying the extended radio emission. A real-time RFI excision system for filtering broadband RFI [2] is developed as part of the GMRT Wideband Backend (GWB). This system uses robust threshold-based detection to identify broadband RFI in the time-domain data for each antenna and polarization. The RFI samples are replaced by digital noise samples. Diverse engineering and astronomical tests have been carried out using this real-time excision technique [3] which show improvements of $\sim10$ dB in the signal-to-noise ratio.