Removal and replacement of interference in tied-array radio pulsar observations using the spectral kurtosis estimator. Issue 2 (27th November 2021)

• Record Type: Journal Article
• Authors: Purver, M; Bassa, C G; Cognard, I; Janssen, G H; Karuppusamy, R; Kramer, M; Lee, K J; Liu, K; McKee, J W; Perrodin, D; Sanidas, S; Smits, R; Stappers, B W
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 510:Issue 2(2022)
• Page Start: 1597
• Page End: 1611
• Publication Date: 2021-11-27
• Subjects: methods: analytical -- methods: data analysis -- methods: numerical -- methods: statistical -- techniques: interferometric -- pulsars: general; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/stab3434
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: We describe how to implement the spectral kurtosis method of interference removal (zapping) on a digitized signal of averaged power values. Spectral kurtosis is a hypothesis test, analogous to the t-test, with a null hypothesis that the amplitudes from which power is formed belong to a 'good' distribution – typically Gaussian with zero mean – where power values are zapped if the hypothesis is rejected at a specified confidence level. We derive signal-to-noise ratios (SNRs) as a function of amount of zapping for folded radio pulsar observations consisting of a sum of signals from multiple telescopes in independent radio-frequency interference environments, comparing four methods to compensate for lost data with coherent (tied-array) and incoherent summation. For coherently summed amplitudes, scaling amplitudes from non-zapped telescopes achieves a higher SNR than replacing zapped amplitudes with artificial noise. For incoherently summed power values, the highest SNR is given by scaling power from non-zapped telescopes to maintain a constant mean. We use spectral kurtosis to clean a tied-array radio pulsar observation by the Large European Array for Pulsars: the signal from one telescope is zapped with time and frequency resolutions of $6.25\, \mathrm{ms}$ and $0.16\, \mathrm{MHz}$, removing interference, along with 0.27 per cent of 'good' data, giving an uncertainty of $0.25\, \mathrm{\mu \mathrm{ s}}$ in pulse time of arrival (TOA) for PSR J1022+1001. We use a single-telescope observation to demonstrate recovery of the pulse profile shape, with 0.6 per cent of data zapped and a reduction from 1.22 to $0.70\, \mathrm{\mu \mathrm{ s}}$ in TOA uncertainty.