Removal and replacement of interference in tiedarray radio pulsar observations using the spectral kurtosis estimator
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 ttest, 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 signaltonoise 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 radiofrequency interference environments, comparing four methods to compensate for lost data with coherent (tiedarray) and incoherent summation. For coherently summed amplitudes, scaling amplitudes from nonzapped 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 nonzapped telescopes to maintain a constant mean. We use spectral kurtosis to clean a tiedarray 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 singletelescope 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.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 February 2022
 DOI:
 10.1093/mnras/stab3434
 arXiv:
 arXiv:2111.14225
 Bibcode:
 2022MNRAS.510.1597P
 Keywords:

 methods: analytical;
 methods: data analysis;
 methods: numerical;
 methods: statistical;
 techniques: interferometric;
 pulsars: general;
 Astrophysics  Instrumentation and Methods for Astrophysics;
 Astrophysics  High Energy Astrophysical Phenomena
 EPrint:
 16 pages, 9 figures