Removal and replacement of interference in tied-array radio pulsar observations using the spectral kurtosis estimator

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.

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.

Citation

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. (2022). Removal and replacement of interference in tied-array radio pulsar observations using the spectral kurtosis estimator. Monthly notices of the Royal Astronomical Society, 510(2), 1597-1611. https://doi.org/10.1093/mnras/stab3434

• Journal Article Type: Article
• Acceptance Date: Nov 22, 2021
• Online Publication Date: Nov 27, 2021
• Publication Date: Feb 1, 2022
• Deposit Date: Nov 29, 2022
• Journal: Monthly Notices of the Royal Astronomical Society
• Print ISSN: 0035-8711
• Electronic ISSN: 1365-2966
• Publisher: Oxford University Press
• Peer Reviewed: Peer Reviewed
• Volume: 510
• Issue: 2
• Pages: 1597-1611
• DOI: https://doi.org/10.1093/mnras/stab3434
• Public URL: https://hull-repository.worktribe.com/output/4134748