RFI at u=0 in MeerKAT observations

Coherent horizontal stripe artefacts caused by low-level RFI coherently adding at the u=0 coordinate on the short baselines are visible in data cubes of deep radio interferometric observations. This affects the characterisation of low-intensity spectral line signal (e.g. neutral hydrogen, HI). In our analysis of 550 scans taken from MHONGOOSE, MeerKAT Fornax Survey (MFS) and MeerKAT open-time observations, we find that these artefacts become visible when the noise in 26.5kHz-binned channels is below 900μJy beam−1. Within our sample, the stripes’ brightness varies with the azimuth and elevation of the target, being most prominent at low elevations in the South-West to East-South-East direction. We describe a method to identify and remove the stripes by using the FFT of a line-free continuum subtracted image. This results in increased image quality and a more Gaussian noise distribution. This method flags, on average, an additional 3% of the visibilities.