Millisecond Cadence Radio Frequency Interference Filters

Abstract

Radio Frequency Interference (RFI) greatly reduces sensitivity of radio observations to astrophysical signals and creates false positive candidates in searches for radio transients. Real signals are missed while considerable computational and human resources are needed to remove RFI candidates. Effective RFI removal is vital to carry out successful searches for fast radio bursts and pulsars. Mitigation techniques that excise RFI on short timescales account for a changing radio frequency and pulse environments. We evaluate the effectiveness of three filters, as well as a novel composite of the three, that excises RFI at the cadence that the data is recorded. Each of these filters operates in a different domain and thus excises as a different RFI morphology. The composite filter removes RFI not accessible to other filtering methods. We analyze the performance of these four filters in three different situations: (i) synthetic pulses in Gaussian noise; (ii) synthetic pulses injected into observed spectra; (iii) test observations of four pulsars. From these tests, we gain insight into how the filters affect both the pulse and the noise level. This allows us to outline which and how the filters should be used based on the RFI present and the characteristics of the source signal. These filters both increase sensitivity and reduce the number of false positives. By flagging less than 5% of the spectrum, we demonstrate a 53% increase in detected pulses and 34% decrease in the number of RFI candidates relative to the Heimdall-Fetch-Your search pipeline.